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The necessity for precise prediction of penetration depth in the context of electron beam welding (EBW) cannot be overstated. Traditional statistical methodologies, including regression analysis and neural networks, often necessitate a considerable investment of both time and financial resources to produce results that meet acceptable standards. To address these challenges, this study introduces a novel approach for predicting EBW penetration depth that synergistically combines computational fluid dynamics (CFD) modelling with artificial neural networks (ANN). The CFD modelling technique was proven to be highly effective, yielding predictions with an average absolute percentage deviation of around 8%. This level of accuracy is consistent across a linear electron beam (EB) power range spanning from 86 J/mm to 324 J/mm. One of the most compelling advantages of this integrated approach is its efficiency. By leveraging the capabilities of CFD and ANN, the need for extensive and costly preliminary testing is effectively eliminated, thereby reducing both the time and financial outlay typically associated with such predictive modelling. Furthermore, the versatility of this approach is demonstrated by its adaptability to other types of EB machines, made possible through the application of the beam characterisation method outlined in the research. With the implementation of the models introduced in this study, practitioners can exert effective control over the quality of EBW welds. This is achieved by fine-tuning key variables, including but not limited to the beam power, beam radius, and the speed of travel during the welding process. [ABSTRACT FROM AUTHOR]

In this paper, an orthomode transducer (OMT) for dual-band operation and optimized for stacked micromachined layers implementation is presented. The proposed design avoids the use of septums, irises, pins, or small features and minimizes the number of equal-thickness micromachined layers required. In this way, the micromachining fabrication is simplified, making the proposed design a very attractive candidate for high frequency applications and for low-cost batch production. A W-band dual-band design (one different polarization in each frequency band) with more than 10% fractional bandwidth for each band and 30% separation between bands is presented. In addition, proper routing and layered bends are designed for an optimum standard interfacing with the same orientation of the input/output ports. Two OMTs in a back-to-back configuration are fabricated using a thick SU-8 photo-resist micromachining process. A total of six stacked SU-8 layers, all of them with the same thickness of \635~\mu\m, are used. The experimental results are coherent with the tolerance and misalignment of the process, validating the proposed novel OMT design. [ABSTRACT FROM AUTHOR]

Bulk metallic glasses (BMGs) are a subject of interest due to their superior specific properties such as low coefficient of friction, high strength, large ductility in bending, high elastic modulus, high microhardness, and high resistance to corrosion, oxidation, wear, and so on. However, BMGs are difficult to apply in industry due to their difficulty in manufacturing and secondary operation. In the past few decades, many efforts have been carried out to overcome the defects in the manufacturing of BMGs. It is difficult to fabricate complex structures with the whole amorphous alloy owing to the limit of crystallization and critical cooling rate. Additive manufacturing (AM), such as selective laser melting (SLM), can obtain relatively high cooling rates during the "layer-by-layer" process, which makes it possible to surpass the dimensional limitation of metallic glass. In the SLM process, the high-speed cooling of molten pool and the avoidance of secondary processing are very beneficial to the production and application of amorphous alloys. In this paper, based on the research of SLM additive manufacturing BMGs in recent years, the factors affecting crystallization and forming ability are discussed from many aspects according to different material systems. The status and challenges of SLM manufacturing BMGs including Fe-based, Zr-based, Al-based, and some composite-based BMGs will be presented. Mechanical properties and physicochemical properties were introduced. This review aims to introduce the latest developments in SLM additive manufacturing BMGs, especially on the development of process parameters, structure formation, simulation calculation, fracture mechanism, and crystallization behavior. With the traditional fabricating methods, BMGs were mainly used as a structure material. It will provide another alternative to use BMGs as a functional material by introducing SLM technology in amorphous preparation with complex geometry. This review summarizes the technical difficulty and application prospects of BMGs preparation by SLM and discusses the challenges and unresolved problems. This review identifies key issues that need to be addressed in this important field in the future. These problems are related to the application of BMGs as high-strength structural materials and new functional materials in the future. [ABSTRACT FROM AUTHOR]

Over the past two decades, laser additive manufacturing technology has evolved rapidly and has been applied in many industrial sectors. The current Special Issue entitled "Recent Advances in Metal Powder-Based Additive Manufacturing" collects the recent research outcomes addressing the main challenges and aiming to provide possible solutions that may revolutionize the metal powder-based additive manufacturing technology and its applications. Significant technical advances have been made in the field of metal powder-based additive manufacturing, and a range of high-performance materials have been successfully developed [[2]]. [Extracted from the article]

Ti-22Al-25Nb alloy containing 0.2 wt. % hydrogen exhibits a sharp yield point on the stress-strain curve when it is tested above 960 °C. The main reason for this phenomenon can be attributed to the unidirectional crystal orientation and low level of lattice distortion above 960 °C, so that the dislocations tend to move in parallel directions with greater mobility and the stress can be rapidly released. Furthermore, strips of brittle α 2 phase can cause stress concentration at the grain boundaries before plastic deformation occurs. Fracturing occurs at the strips of α 2 phase when micro-deformation occurs, so that the accumulated stresses are rapidly released. [ABSTRACT FROM AUTHOR]

Predicting the penetration depth during electron beam welding (EBW) is important, but the accuracy of current predictive models is highly varied, depending on the type and number of data used. This paper develops and compares several penetration depth prediction models for EBW and uniquely compares the influence of the number and type of data used, as well as the measurement and modelling methods. Although accelerating voltage, beam current and welding speed data are essential modelling inputs, additional data for beam focal position and beam shape, measured using a novel 4-slit beam probing method, greatly improve the accuracy of predictions for models based on an empirical equation, a second-order regression and an artificial neural network (ANN). Optimised models predict weld depths that deviate, on average, by less than 5% from measured depths, are valid for very broad linear electron beam power density ranges (86–324 J/mm) and are close to the estimated 4% inherent variability in the process and its measurement. Within this linear electron beam power density range, the ANN yields accurate and reliable depth predictions, demanding as few as 36 welding trials, decreasing the number required for models that do not consider beam focal position and shape, for the same targeted accuracy, by more than 60%. Adding large volumes of virtual data generated by less reliable analytical or regression models did not improve the predictive capability for the ANN developed in this study. [ABSTRACT FROM AUTHOR]

In-process penetration monitoring of the pulsed laser welding process remains a great challenge for achieving uniform and reproducible products due to the highly complex nature of the keyhole dynamics within the intense laser-metal interactions. The main purpose of this study is to investigate the feasibility of acoustic emission (AE) measurement for penetration monitoring based on acoustic wave characteristics and deep learning. Firstly, a series of laser welding experiments on aluminum alloys were conducted using high-speed photography and AE techniques. This allowed us to in-situ visualize the complete keyhole dynamics and elucidate the generation mechanism of acoustic waves originating from pressure fluctuations at the keyhole wall. Then, an adaptive time-frequency technique namely VMD (Variational Mode Decomposition) was proposed to characterize the acoustic energy distribution among the nine subsignals with low-frequency and high-frequency components under different welding penetrations. Lastly, a novel hybrid model combing CNN (Convolutional Neural Network) and LSTM (Long Short Term Memory) was designed to deeply mine the spatial and temporal acoustic features from the extracted frequency components. Extensive experiments demonstrate that our proposed approach yields a remarkable classification performance with a test accuracy of 99.8% and a standard deviation of 0.21, which obtains a high recognition rate. This work is a new paradigm in the digitization and intelligence of the laser welding process and contributes to an alternative way of developing an efficient end-to-end penetration monitoring system. [ABSTRACT FROM AUTHOR]

The composite fillers have a number of advantages comparing with the traditional filler metals, and have been widely used for brazing ceramics. However, previous researches mainly focus on the strengthening mechanism of either whiskers or particles. It is still of great interest to investigate the reinforcement effect with the presence of both whiskers and particles. In this study, Ag-Cu-Ti + B 4 C composite filler was developed to braze SiC ceramics, and effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated in detail. With the prolongation of holding time, the overall thickness of Ti 3 SiC 2 + Ti 5 Si 3 layers adjacent to SiC ceramic was increased correspondingly and the reaction between active Ti and B 4 C particles was promoted more extensively. The bending strength of the joints increased with holding time until the maximum bending strength of 140 MPa was reached and then decreased dramatically. The hardness and Young's modulus of the joints were characterized by nano-indentation to reveal the strengthening of the brazing seam. In addition, the strengthening mechanism of the joints brazed by the Ag-Cu-Ti + B 4 C composite filler was proposed on the basis of experimental observation and theoretical analysis. [ABSTRACT FROM AUTHOR]

The corrosion resistance and biocompatibility of a novel Fe50Cr18Mo10C20Si2 metallic glass (Fe–MG), are studied by electrochemical measurements and indirect contacting cytotoxicity assays for biomedical applications. In Hank's solution, the Fe–MG shows better corrosion resistance than SS316L, evidenced by the larger polarization resistance in the potentiodynamic and electrochemical impedance spectroscopy (EIS) tests, and the lower amounts of released metallic ions during the immersion test. X-ray photoelectron spectroscopy (XPS) analyses show that a double-layer passive film, consisting of outer Fe-rich oxide and inner Cr-rich oxide, is formed on the Fe–MG. The stable passive film, together with the defect-free nature of the metallic glass, accounts for good corrosion resistance. In addition, in vitro tests suggest that the Fe–MG extracts have good blood compatibility, and no cytotoxicity to murine fibroblast cells. Compared with other Fe-based metallic glasses, the prepared novel Fe–MG contains no toxic elements, and shows a low corrosion rate. [ABSTRACT FROM AUTHOR]

Background: The enlarged vestibular aqueduct (EVA) is the commonest malformation of inner ear accompanied by sensorineural hearing loss in children. Three genes SLC26A4, FOXI1, and KCNJ10 have been associated with EVA, among them SLC26A4 being the most common. Yet, hotspot mutation screening can only diagnose a small number of patients. Methods: Thus, in this study, we designed a new molecular diagnosis panel for EVA based on multiplex PCR enrichment and next‐generation sequencing of the exon and flanking regions of SLC26A4. A total of 112 hearing loss families with EVA were enrolled and the pathogenicity of the rare variants detected was interpreted according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Results: Our results showed that 107/112 (95.54%) families carried SLC26A4 biallelic mutations, 4/112 (3.57%) carried monoallelic variants, and 1/112 (0.89%) had none variant, resulting in a diagnostic rate of 95.54%. A total of 49 different variants were detected in those patients and we classified 30 rare variants as pathogenic/likely pathogenic, of which 13 were not included in the Clinvar database. Conclusion: Our diagnostic panel has an increased diagnostic yield with less cost, and the curated list of pathogenic variants in the SLC26A4 gene can be directly used to aid the genetic counseling to patients. [ABSTRACT FROM AUTHOR]

A near-equiatomic FeCoNiCuAl High-entropy alloy (HEA) was produced using laser powder bed fusion (L-PBF) pre-alloy powder. Microstructural characteristics and tribological properties of L-PBF specimens under various volumetric energy densities (VEDs) were investigated in detail. The results showed that the phase of L-PBF specimen consisted of BCC matrix + Cu-rich B2 precipitate. The microstructure of L-PBF specimen largely consisted of columnar grains perpendicular to the melt pool boundary (MPB) direction owing to the epitaxial growth along the temperature gradient. The preferred orientation of the L-PBF specimen was gradually transformed from the order of <001> to <101> as the VED rose. Larger size precipitates re-appeared and wider MPB were formed upon faster remelting and steeper cooling as a result of higher VED. Compared to the components produced by Spark Plasma Sintering, L-PBF specimens presented better wear resistance owing to the ultra-fine substructure and nano-scaled precipitates. In addition, the L-PBF specimen produced with 83 J/mm3VED exhibits the highest elastic strain to failure (H/Er) and yield stress (H2/Er3). [ABSTRACT FROM AUTHOR]

WC-Co hardmetals are widely used in wear-resistant parts, cutting tools, molds, and mining parts, owing to the combination of high hardness and high toughness. WC-Co hardmetal parts are usually produced by casting and powder metallurgy, which cannot manufacture parts with complex geometries and often require post-processing such as machining. Additive manufacturing (AM) technologies are able to fabricate parts with high geometric complexity and reduce post-processing. Therefore, additive manufacturing of WC-Co hardmetals has been widely studied in recent years. In this article, the current status of additive manufacturing of WC-Co hardmetals is reviewed. The advantages and disadvantages of different AM processes used for producing WC-Co parts, including selective laser melting (SLM), selective electron beam melting (SEBM), binder jet additive manufacturing (BJAM), 3D gel-printing (3DGP), and fused filament fabrication (FFF) are discussed. The studies on microstructures, defects, and mechanical properties of WC-Co parts manufactured by different AM processes are reviewed. Finally, the remaining challenges in additive manufacturing of WC-Co hardmetals are pointed out and suggestions on future research are discussed. [ABSTRACT FROM AUTHOR]

Variable polarity cold metal transfer (VPCMT) is a newly developed welding process and has drawn extensive interests because of its potential in further reducing the heat input, offering greater gap bridging ability, and improving the deposition rate. Using 6061 aluminum alloy as an example, this paper systematically investigated the influences of the key parameter in VPCMT, i.e., "positive/negative electrodes ratio (EP/EN Balance)," on weld formation, microstructure, and mechanical properties. It was found that, with the increase of the EP/EN Balance value, the duty cycle of the negative phase was reduced but the peak current and maximum temperature of the weld pool were both increased resulting in a higher heat input. The positive/negative electrode ratio had little impact on the grain misorientation angle in the fusion zone. Hardness of the joint was higher with larger positive duty cycles because of the precipitate phase and small grain size. An increased negative duty cycle resulted in lower heat input leading to insufficient melting of the material and deterioration of the mechanical strength of the welds. [ABSTRACT FROM AUTHOR]

A crack-free Fe-Cr-Mo-C-Y-B amorphous coatings has been prepared on the surface of Q235 steel by the method of magnetic-field-assisted laser cladding. The uniformity of the distribution of elements in the coating is increased by alternating the magnetic field, which increases the plastic toughness of the coating. The mechanical behaviour of indentation points after nanoindentation of the coated sample was observed by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

In order to obtain a laser-cladded coating with no cracking and good corrosion resistance, this paper investigated laser cladding of a mixture of 17-4PH stainless steel and Ni60 powders on ASTM 1045 steel substrate. The surface cracking, mechanical properties and corrosion resistance of the coatings were assessed by various characterization methods. The experimental results demonstrated that a crack-free coating can be obtained by adding 30% (or above) 17-4PH stainless steel into Ni60 alloy. The mechanical properties of the coatings were determined by adding 17-4PH, but stabilized at about 79% of pure Ni60 alloy, which is acceptable considering the benefit of elimination of surface cracking. Decrease in the mechanical properties were caused by the dilution of the strengthening elements and reduction of population of hard phases. Composite coating having 30% of 17-4PH also exhibited the smallest corrosion current, lowest corrosion potential and slowest corrosion rate, and therefore the best corrosion resistance. [ABSTRACT FROM AUTHOR]

• We review the current state of research in femtosecond and nanosecond laser processing of metallic glass surfaces. • The microscopic changes in the material by the action of femtosecond and nanosecond lasers are reviewed. • The mechanisms of micro- and nanostructure evolution on metallic glass surfaces are presented. • The mechanical properties, optical properties, wettability and biocompatibility of metallic glass surfaces after laser irradiation are reviewed and discussed. In recent years, the number of research work on the surface modification of metal glass by laser processing has been increasing, indicating that the interaction between laser and metal glass surface is interesting. Short pulse laser and ultrashort pulse laser processing are the most prominent in this field because of their narrow pulse width, high energy density and short action time with materials. In particular, femtosecond lasers and nanosecond lasers provide great possibilities for high quality, high efficiency and low loss processing of metal glass. This review summarizes this specific research field, introduces the properties and applications of metallic glass, the processing characteristics of femtosecond lasers and nanosecond lasers, and explains the complex process between laser and metallic glass from a microscopic perspective. In addition, this paper also analyzes the micro-nano structure and macroscopic morphology, and discusses the influence of microscopic mechanism on the structure. On the other hand, the properties of micro-nano structure are also discussed, including mechanical properties, optical properties, wettability and biocompatibility, which is of great significance to the surface functionalization of metallic glass. [ABSTRACT FROM AUTHOR]

In this study, in order to achieve a better understanding of the strengthening mechanism in the commercially pure (CP) Ti welds, autogenously laser beam and laser-MIG hybrid welding of 4.2 mm thick CP-Ti plates were performed and the correlation between microstructure, texture distribution and the mechanical properties were systematically investigated. Microstructural coarsening and increase in microhardness were observed in the HAZ and WZ. The tensile test results suggested the base metal was the weak point of the joint for both welding conditions. The EBSD observations confirmed that a large number of 101¯2 and 112¯2 twin grains occurred in the HAZ and WZ of both welded joints, while a higher concentration of these twin grains were found in the laser-MIG hybrid joints. High concentration of the twin grain boundaries can act as barrier to stop dislocation slip during deformation and therefore contribute to the strengthening of the welds. The existence of very small twin grains and acicular α phase in HAZ and WZ would equivalently reduce the averaged grain size and therefore induce an increase in strength based on Hall-Petch's law. In addition, the averaged Schmid factor of BM is higher than that of the WZ and HAZ in both welding joints suggesting that the grain boundary sliding will take place preferably in BM during deformation so that the necking and fracture occurred in base metal during tensile tests of both welding joint specimens. [ABSTRACT FROM AUTHOR]

• Experimental tests on 3D printed stainless steel stub columns and tensile coupons have been carried out. • Numerical modelling validation and subsequent parametric study has been performed. • 'Higher-order' wave patterns can increase plate buckling resistances. • Optimum wave patterns have been identified. • Provisional design equations have been proposed for the optimised shapes. This paper reports the first experimental tests on additively manufactured steel plates stiffened by sinusoidal waves, followed by a detailed numerical modelling programme to account for the imperfection sensitivity of these shapes. This innovative study focuses on stiffened plates (plates simply supported along both longitudinal edges), which were experimentally tested employing square hollow section (SHS) stub columns. The experimental study comprised of 5 tensile coupon tests, 15 stub column tests and measurements on geometric accuracy and residual stresses on 316L stainless steel samples made by selective laser melting (SLM). Validating against the experimental results, numerical models accounting for realistic manufactured dimensions and geometric imperfections have been developed. The validated numerical models were used to perform a parametric study considering a wider range of geometries and plate slendernesses. Based on the results of the parametric study, the efficiency of this stiffening method across a range of plate slendernesses has been assessed and optimum wave patterns identified, which were shown to be able to enhance buckling strength up to 50% compared to the flat counterparts. Provisional design equations have also been proposed for SLM 316L stainless steel plates stiffened by the optimum stiffening patterns selected. [ABSTRACT FROM AUTHOR]

Light metal/carbon fiber reinforced polymer (CFRP) hybrid structures have been considered a key component for lightweight and advanced multi-material structures in modern automotive and aerospace applications. In this study, directional physicochemical surface pretreatment routes based on the conceptual process of geometric configuration and chemical modification were designed for the reliable joining of A6061 aluminum alloy (Al alloy) and carbon fiber reinforced polyamide 66 (CFRP) via friction stir lap welding (FSLW). The effects of surface pretreatment parameters were clarified and an effective coupled treatment strategy was proposed. Micro-textures with uniform geometric grooves with average width w = 13.17 ± 3.27 μ m and average depth d = 122.45 ± 12.83 μ m processed by laser ablation (LA) and flower-like AlOOH nanostructures synthesized by hot water treatment (HWT) promoted mechanical interlocking and chemical bonding at the macro/micro/nanoscale. For this reason, the high interfacial bonding strength of 30.2 MPa and joint efficiency of 67.2% were achieved, and continuous superficial resin of the CFRP matrix adhered to the fracture surface of Al alloy during the failure process. More effectively, the interfacial structures and chemical compositions were analyzed by transmission electron microscopy (TEM), and the formation of C-O-Al and hydrogen bonds was attributed to the γ-Al 2 O 3 ·yH 2 O layer and AlOx·yH 2 O atom clusters, which was verified to enhance the interfacial bonding. This first exploratory study on Al alloy/CFRP interfacial bonding at the nanoscale based on physicochemical coupling surface pretreatment provides an in-depth understanding of the joining of light metals and polymer-matrix composites. • Directional physicochemical surface pretreatment routes based on the process concept of geometric configuration and chemical modification were designed. • Micro-textures processed by laser ablation (LA) and flower-like AlOOH nanostructures synthesized by hot water treatment (HWT) promoted the mechanical interlocking and chemical bonding effect at micro/micro/nanoscale. • The maximum interfacial bonding strength of 30.2 MPa was achieved with coupling surface pretreatment, and local failure region transformed from joined interface to CFRP matrix. [ABSTRACT FROM AUTHOR]

• We review the important theory of the laser-induced material formation of periodic micro-nanostructures. • The physical processes of interaction between ultrashort pulse laser and materials are reviewed in this paper. • The principle of two-temperature simulations is introduced and discussed thoroughly by the two-temperature model. • Review and discuss seven typical complex simulations based on a two-temperature model. The generation of periodical micro-nanostructures by laser-induced materials with ultrashort pulses has been a research hotspot in recent years and has been used extensively in many fields. There is a lot of research being done on laser-induced periodic surface structures (LIPSS, ripple) in the areas of navigation, medicine, aerospace, biology, etc. The study of laser ablation is greatly influenced by the intricate physical process of interaction between an ultrashort pulse laser and the material. In order to more successfully conquer this challenge, this paper reviews the ultrashort pulse laser ablation, induced material surface formation of periodic surface structure important theory, including the electromagnetic theory and matter reorganization theory. By summarizing the complex physical processes of ultrashort pulse laser ablation, review the most popular two-temperature model in contemporary ultrashort pulse ablation simulation. The effect of the two-temperature model on the development of ultrashort pulse laser technology is analyzed. By discussing using a two-temperature model to enhance the single-pulse laser ablation analysis and promote the understanding of the periodic micro-nano structures generated on the material's surface by ultrashort pulse laser ablation. This paper introduces a variety of complex two-temperature model methods to simulate the interaction between ultrashort pulse laser and metal. The main difficulties faced by ultrashort pulse laser processing are listed, and suggestions for simulation of ultrashort pulse laser processing in the future are put forward. [ABSTRACT FROM AUTHOR]

The effect of different laser scanning speeds on the microstructural evolution and associated tribological and corrosion behavior of Ti-23Nb alloys produced by laser metal deposition (LMD) was systematically investigated. The microstructures of all specimens were composed of equiaxed β grains, acicular α″ phases, and unmelted Nb particles. With the increase of scanning speed, the volume fractions of the α″ phase and unmelted Nb particle increased, while the volume fraction and grain size of the β phase decreased. This results in a high hardness (∼ 304 HV) for the specimen with a high scanning speed (2.6 mm/s). Although the hardness of the specimen produced at 2.0 mm/s is slightly lower (∼ 296 HV), it possesses less unmelted Nb particles (soft phases, low hardness of ∼ 107 HV), resulting in a lower wear rate (∼ 4.9 × 10−4 mm3N−1 m−1). Compared to fully alloyed areas, unmelted Nb particles corrode preferentially. The specimen produced at 2.6 mm/s possesses a lower corrosion potential (E corr) value owing to the presence of more α″ phase and unmelted Nb particles. Grain size is a critical factor in determining the corrosion current density (i corr). The high scanning speed specimen (2.6 mm/s) with small grain sizes has high resistance and low i corr. • The microstructures of LMD Ti-23Nb alloys were composed of equiaxed β grains, acicular α″ phases, and unmelted Nb particles. • Localized partitioning of solutes is the underlying reason for the formation of α″ martensite during LMD processing. • Grain size and unmelted Nb particles are two main factors for the properties of LMD Ti-23Nb alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crack-free CoCrNi laser directed energy deposition additive parts successfully obtained at high heat input. • High-angular grain boundary stress concentrations and excessive oxygen content in the additive parts were the main reasons for the crack formation. • Three crack suppression strategies could be proposed from this study, namely, reducing the heat input, performing additive experiments under argon-filled environment, and decreasing the oxygen content of the powder. Laser-directed energy deposition (l -DED) additive manufacturing of the CoCrNi medium entropy alloy is prone to cracking, especially with high laser heat input. Electron backscatter diffraction analysis showed crack formation and stress concentration at the high-angle grain boundaries. In addition, element content test results exhibited a higher oxygen content in the additive parts with high laser heat input. Electron probe X-ray microanalysis indicated that the oxygen was distributed uniformly in the additive parts. Corresponding molecular dynamics simulation results revealed that an increase in oxygen content led to a decrease in the tensile strength of the additive parts. Two methods of argon-filled environment l -DED experiments and low-oxygen CoCrNi feeding power (argon gas atomization) were used. Results showed that the number and size of cracks were significantly reduced in the additive parts obtained by a high heat input process when the l -DED was conducted in an argon-filled atmosphere and when powders with lower oxygen content were used. For the crack-free additive parts, the ultimate tensile strengths reached 625 MPa with high laser heat input. Three crack suppression strategies could be proposed from this study, namely, reducing the heat input, performing additive experiments under argon-filled environment, and decreasing the oxygen content of the powder. [ABSTRACT FROM AUTHOR]

In this paper, changes in the morphology and composition of the O, α 2 and B2/β phases and the transformation relationship between the three phases of Ti 22Al 25Nb alloy were systematically investigated by performing a series of short heat treatments. The results showed that the phase transformations can be divided into three stages in the temperature range of 870 °C ~ 1080 °C. In the first stage of 870 °C ~ 930 °C, the O phase started transferring to α 2 + B2 first along grain boundaries with lamellar morphology due to short-range diffusion, and the O → α 2 + B2 reaction was accompanied by a large amount of Nb segregation. With the increase in temperature, the phase transformation migrated from the boundaries to the inside of the grains, and the α 2 -phase spheroidized gradually. In the second stage from 960 °C to 1020 °C, granular α 2 and B2 phases precipitated directly from the O phase due to long-range diffusion. At 1020 °C, the O → α 2 + B2 transition was completed and the granular α 2 phase mainly populated along the grain boundaries. In the third stage above 1020 °C, the main phase transformation was α 2 → B2, and the aggregation and growth of the α 2 phase were observed in α 2 -rich regions. [ABSTRACT FROM AUTHOR]

In this essay, a femtosecond laser is used to create various structures on the surface of Zr-based amorphous material. Through the raster scan mode, under different laser energy densities, LIPSS (Laser-induced periodic surface structures), SWPSS (Super-wavelength periodic surface structure) and microporous structures were obtained in the experiment. Various surface properties of the micro-nano structures were tested. Experimental results illuminate that laser energy fluence is the key to determining the formation of nano- and microscale structures. The laser treatment greatly improves the surface roughness of the sample. The laser texture converts the originally hydrophilic specimen surface into a hydrophobic surface, which greatly reduces the material's surface energy. We found that all the formed surface structures can reduce the adhesion of Escherichia coli and Staphylococcus aureus. In detail, the adhesion rate of bacteria on the surface of SWPSS is the lowest. This article comprehensively discusses the influence mechanism of nano- and microscale structures on bacterial adhesion from four aspects: surface roughness, hydrophobicity, surface energy, and surface morphology. The study manifest that the period and amplitude of the nano- and microscale structures are the keys to bacterial adhesion. In addition, experiments have shown that nano- and microscale structures can effectively improve the corrosion resistance of zirconium-based bulk metallic glass. [ABSTRACT FROM AUTHOR]

Both a novel Ti-5Cu alloy (in wt%) and a Ti-5Cu in situ composite containing 1 wt% B 4 C were fabricated by laser powder bed fusion, and their microstructures, mechanical and tribological properties were systematically investigated. The microstructure of the Ti-5Cu was mainly composed of α Ti laths, Ti 2 Cu and retained β phases, while the B 4 C/Ti-5Cu composite was composed of α Ti laths, Ti 2 Cu, TiC, TiB and TiB 2 phases. Both the Cu and B 4 C additions promoted a transition from columnar to equiaxed grains for prior-β and α phases. The B 4 C/Ti-5Cu composite was found to have a higher hardness (467 HV) than the Ti-5Cu (417 HV). Further, the composite exhibits a yield strength of 1100 MPa and an ultimate tensile strength of 1250 MPa. Values which are higher than those of the Ti-5Cu that exhibits a yield strength of 750 MPa and an ultimate tensile strength of 900 MPa. However, this strength increase comes at the expense of a reduction in elongation to failure from 6.2% to 1.5%. Even though the composite is significantly stronger, the two materials exhibited very similar wear rates (ω B4C/Ti-5Cu = 4.95 × 10−4 mm3 N−1 m−1 and ω Ti-5Cu = 4.85 × 10−4 mm3 N−1 m−1). • The LPBFed Ti-5Cu was mainly composed of α Ti laths, Ti 2 Cu and retained β phases. • The LPBFed B 4 C/Ti-5Cu composite was composed of α Ti laths, Ti 2 Cu, TiC, TiB and TiB 2 phases. • Both the addition of Cu and B 4 C can refine the grain and promote columnar to equiaxed transition of prior-β phase. • The LPBFed Ti-5Cu exhibit a strong combination of hardness, tensile properties and wear resistance. • Although the composite is significantly stronger, the two materials exhibited very similar wear rates. [ABSTRACT FROM AUTHOR]

Due to their bioinert nature, titanium alloys show poor bone-implant integration and insufficient osseointegration in vivo. In this study, a series of low elastic modulus bioactive titanium alloys with a nominal composition of Ti-13Nb-13Zr-1.25 Mg (wt%) were prepared using mechanical alloying and spark plasma sintering techniques. The microstructures, mechanical properties, degradation behaviors and in vitro bioactivities of these alloys were systematically investigated. After sintering at 700 °C, the α-Ti, β-Ti and Nb (Zr)-rich phases were present, and the Mg was uniformly distributed. In addition to above-mentioned phases, the α″ phase was found after sintering at 800 °C or 900 °C. The density, elastic modulus, yield strength, ultimate compressive strength and corrosion resistance all increased with increasing sintering temperature. After sintering at 900 °C, the alloy exhibited high density (99.8%), good compressive strength (1417.2 MPa) and excellent corrosion resistance. In addition, it had a lower elastic modulus (~69 GPa) than that of the biomedical alloy Ti–13Nb–13Zr (~80 GPa). In vitro experiments showed that the alloys sintered at either 800 °C or 900 °C promoted cell adhesion and proliferation. However, the alloy sintered at 700 °C inhibited cell proliferation, which was due to the greater release of Mg2+. Thus, the optimally-processed Ti-Nb-Zr-Mg alloy sintered at 900 °C shows immense potential as a biomedical material. [Display omitted] • Ti-Nb-Zr-Mg alloys with low modulus were fabricated by MA and SPS. • Higher sintering temperature promoted the formation of α″ phase. • Mg element reduced the corrosion resistance of Ti-Nb-Zr matrix. • The mode of Mg2+ release was affected by sintering temperature. • The sustained release of Mg2+ was beneficial to the cell viability and proliferation. [ABSTRACT FROM AUTHOR]

The development of additive manufacturing technology has made it possible to customize joint implants. However, the fibrous tissue caused by long-term chronic inflammation delays bone regeneration. Moreover, the discovery of micro/nano-structure on the natural bone makes the study of implant surface morphology meaningful. In this study, a Sr-containing nano-structure on micro-structured titanium alloy surface was fabricated to enhanced the anti-inflammatory and osteogenic properties of implants. Ti6Al4V (TC4) alloys with micro-structured surface prepared by additive manufacturing were used as the material base model. Subsequently, spherical SrTiO 3 particles were fabricated on the TC4 surfaces by hydrothermal treatment. The anti-inflammatory and osteogenic performance of smooth surface, micro-structured surface, Sr-containing nano-structured surface and Sr-containing micro/nano-structured surface were investigated. In vitro results exhibited that the macrophages cultured on micro/nano-structured surface were polarized to anti-inflammatory M2 phenotype and enhanced the expression of osteogenic growth factors. The Sr-containing micro/nano-structured surface effectively upgraded the proliferation and differentiation of SaOS-2 cells compared with other surfaces. Sr2+ and micro/nano-structure effectively enhanced the anti-inflammatory and osteogenic properties of titanium alloys. This finding suggested that the micro/nano-structured surface doped with bioactive elements is expected to broaden the horizons of biomedical materials. The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. [Display omitted] • TC4 alloys with micro-structured surface were fabricated by SLM technique. • The nano-structures of SrTiO 3 were fabricated by hydrothermal technology. • Sr2+-containing micro/nano structure down-regulated the expression of pro-inflammatory genes. • The osteogenic differentiation potential of macrophages was promoted on the micro/nano-structured surface. • Micro/nano-structured surface boosted the proliferation and differentiation of osteoblast-like cells. [ABSTRACT FROM AUTHOR]

In this paper, we describe the effects of different scanning speeds (600–900 mm/s) on the microstructure, mechanical properties and corrosion behavior of biodegradable bone-substitution alloys produced from 80:20 (by wt.) Fe:Mn powders using laser powder bed fusion (LPBF). Both the Mn content (18.9–15.1 wt% Mn) and density (7920–7730 kg/m3) of the LPBFed samples decreased slightly with increasing laser scanning speed, while the oxygen content increased (0.12–0.40 wt%). Increasing scanning speed also led to increased porosity (from 0.27% to 2.5%) and increased cracking. The specimen produced at the lowest scanning speed of 600 mm/s, which consisted of only the HCP ε-martensite phase, showed by far the highest yield strength (YS) at 644 MPa and the highest ultimate tensile strength (UTS) at 857 MPa, but the lowest elongation to failure (El) of only 13.7%. Specimens produced at higher scanning rates consisted of both BCC α′-martensite and ε-martensite phases. The sample fabricated at a scanning speed of 700 mm/s showed the best balance of mechanical properties with a YS of 330 MPa, a UTS of 839 MPa, and an El of 36.1%. Electrochemical testing showed corrosion rates from 0.09 mm/yr (600 mm/s specimen) to 0.22 mm/yr (700 mm/s specimen), which are higher than those of both pure Fe and most Fe–30Mn and Fe–35Mn alloys reported in the literature. The work demonstrates that the meso-/micro-scale structure, and, hence, the mechanical properties and corrosion rates of Fe–Mn alloys can be tailored by varying the scanning speed during LPBF processing. It also demonstrates the potential of LPBFed Fe–Mn alloys with low Mn content for use as biodegradable bone substitutes. [ABSTRACT FROM AUTHOR]

9Cr steel is a material that has been widely used in pressure vessel parts in thermal power plants and nuclear power plants, and has good high-temperature creep properties. Laser Melting Deposition (LMD) is a promising method for preparing complex 9Cr steel components. It provides a rare opportunity to improve existing designs and produce fine features and complex geometries with higher efficiency. The LMD-9Cr steel sample has high density, the maximum tensile strength of the sample is 1057.75 MPa, which is much higher than the standard cast 9Cr steel of 650 MPa. We use 760 °C tempering heat treatment, after heat treatment, the average grain size of the material is reduced, the Charpy impact performance is improved, and the tensile strength and microhardness are slightly reduced. Although the tempering heat treatment greatly reduces the average grain size of the sample by 35.59%, but at the same time the tempering heat treatment greatly reduces the high dislocation density of lath martensite, and the supersaturation behavior of Cr, W and C elements weakens the effect of solid solution strengthening. In addition, through the nanoindentation test, we found that although the M 23 C 6 precipitated phase can harden the material, at the micro level, the elastic modulus and nano-hardness of the precipitated phase are lower than that of the homogeneous phase. • 9Cr steel was fabricated by laser coaxial powder feeding additive. • C The constructed LMD-9Cr sample has high density, the maximum tensile strength of the sample is 1057.75Mpa, which is much higher than the standard cast 9Cr steel of 650 MPa. • Tempering heat treatment greatly reduces the high dislocation density of lath martensite Effect of crystallization on mechanical properties. [ABSTRACT FROM AUTHOR]

To simultaneously obtain superior superelasticity and biological properties, single- and multi-layer Ti–23Nb coatings were deposited on a cold-rolled NiTi substrate using laser metal deposition (LMD). The microstructure of the single-layer coating consisted of a cellular structure with a grid size of ∼300 μm in the eutectic layer, strip structures and prior β-(Ti, Nb) phases surrounded by the Ti 2 Ni(Nb) phase in the Ni diffusion zone. In contrast, the microstructure of the multi-layer coating consisted of α′, α′′, and prior β phases, which arise from the partition of Nb. Compared with the NiTi substrate, the Ni ion release concentration of the single-layer coating is reduced by 45% with similar nano-mechanical behavior, i.e. a nanohardness, H , of ∼4.0 GPa, a reduced Young's modulus, E r , of ∼65 GPa, an elastic strain to failure, H / E r , of ∼0.06, a yield stress, H 3/ E r 2, of ∼0.016 GPa, and a superelastic strain recovery, η sr , of ∼0.3. The reduction of Ni ion concentration for multi-layer coating after 35 days is even better at up to 62%, but at the cost of a degradation in the mechanical properties. The LMD coatings have a high dislocation density, and their creep is controlled by dislocation movement. • The diffusion of Ni during laser melting leads to the formation of cellular and strip subgrains. • α″ martensite is critical for the properties of the TiNb binary alloys produced by LMD. • The single-layer coating can suppress the release of Ni ions while preserving the superelasticity of substrate. [ABSTRACT FROM AUTHOR]

Although 2-d (two-dimensional) beam oscillation can reduce the porosity defects during laser welding of aluminum alloys, it distributes the heat input, resulting in a higher power required to form a capillary. Therefore, this research draws attention to an alternative approach, which is considered to be beneficial to laser absorption in oscillation laser beam welding, 3-d (three-dimensional) oscillation of the laser beam. (3-d oscillation means that the laser spot moves on the two-dimensional plane and the defocus change simultaneously, causing the heat input to change) An experiment was designed where the variation of oscillation frequency leads to significant changes in capillary behavior. The result shows that the increase of vertical oscillation can promote the formation of a capillary. When the oscillation frequency reaches some special values, the capillary appears and disappears periodically, such as the vertical oscillating frequency is 5 Hz, rotation oscillating frequency is 200 Hz. Meanwhile, welding pores are generally distributed at the position where the capillary begins to disappear. The reason for promoting capillary formation during 3-d laser beam oscillation, and the change of normalized temperature, which is meaningful for understanding the welding mode transition, is illustrated by a simplified model. Compared with traditional linear welding, the experimental results show that it is possible to obtain lower porosity seam during 3-d laser beam oscillation welding in low feed rate, and the mechanism of stabilizing the molten pool is discussed qualitatively. [ABSTRACT FROM AUTHOR]

FeCoCrNiMo high-entropy alloy (HEA) has attracted great interests due to its excellent corrosion resistance, but it suffers relatively low hardness and poor tribological performance. In this work, a systematic study on microstructural evolution and tribological behavior of equiatomic FeCoCrNiMoSi x (x = 0.5, 1.0, 1.5) HEA coatings prepared by laser cladding (LC) on Q235 steel substrates is reported. Confirmed by X-ray diffraction analysis (XRD) and energy dispersive spectrometry (EDS) results, these coatings mainly consist of Fe-rich FCC and FeMoSi phases. The increase of Si content leads to greater lattice distortion and promotes the formation of Si-rich intermetallics, which can significantly improve the hardness and the wear resistance of the FeCoCrNiMoSi x coatings. The best wear resistance is achieved in FeCoCrNiMoSi 1.0 coating, which the wear mechanism is a combined abrasive and adhesive wear. • FeCoCrNiMoSi x (x = 0.5, 1.0, 1.5) HEA coatings were fabricated by laser cladding. • Single track experiments were used to figure out the optimal process parameters. • The FeCoCrNiMoSi x HEAs mainly consisted of Fe-rich FCC, FeMoSi phases and Si-rich intermetallics. • Hardness of 943 HV was obtained in FeCoCrNiMoSi 1.5. • Wear mechanism changed from abrasive and adhesive wear to delamination wear. [ABSTRACT FROM AUTHOR]

• Manufacturing bulk metallic glass (BMG) by selective laser melting (SLM). • Process parameters of SLM-BMG. • Crystallization analysis in the manufacturing process of BMG. • Annealing of metallic glass. • Effect of crystallization on mechanical properties. Fe-based bulk metallic glass (BMG)(FeCrMoWMnSiBC) was produced by selective laser melting (SLM) successfully in this study. The best parameters were determined through extensive experiments. The relative density (95%) and amorphous rate (95.47%) samples were obtained by this parameter. The analysis of the microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly α-Fe and M 23 (CB) 6 phases, and co-exist with the amorphous phases. The Heat treatment is employed to study the crystallization behavior of amorphous phases. The α-Fe phase, as the primary phase, grows into a submicron crystal phase under the action of multiple thermal cycles. Nanoindentation test results show that the hardness of the amorphous phase is higher than that of the nano-grain region, and the hardness of the nanocrystalline region is higher than that of the submicron-grain region. The free volume content is different and the amorphous phase is not uniform due to the complex thermal cycle. The maximum hardness occurs in the amorphous phase with 22.6 GPa. [ABSTRACT FROM AUTHOR]

• Femtosecond laser induces LIPSS, SWPSS and microporous structure on Zr-based amorphous.. • Compare the period, amplitude, surface fluctuation and roughness of different micro-nano structures. • The effective energy density increases, LIPSS transitions to SWPSS, and finally into a self-organized microporous structure.. • The micro-remelting caused by the heat accumulation effect is the key to the transformation of the micro-nano structure. • The self-organized microholes structure has the great ability to reduce E. coli adhesion. Laser induced micro-nano texture formation on the surface of solid materials has become a research hotspot in the field of material surface modification. However, due to its extremely easy crystallization characteristics, the study of laser-induced surface modification of bulk amorphous alloy lags behind. In this study, femtosecond laser was used to induce one-dimensional LIPSS (Laser-induced periodic surface structures), SWPSS (Super-wavelength periodic surface structure), a mixed state structure of LIPSS + SWPSS and two-dimensional self-organized microholes structure on surface of the Zr55Cu16Ni15Ti10Al4 bulk amorphous alloy. The numerical difference between LIPSS, SWPSS and self-organized microholes structure in different dimensions such as period, groove width, profile height, etc. were compared, and the roughness of different micro-nano textures and the size of surface undulations were evaluated. The effects of different process parameters on the formation and transformation of micro-nano texture on the surface of zirconium bulk amorphous alloys were investigated. The mechanism of the transformation from LIPSS to SWPSS and finally to two-dimensional self-organized microholes structure was analyzed in detail. Finally, Escherichia coli was cultured on the amorphous surface of Zr-based metallic glasses with different structure. To examine the effect of micro-nano texture on the antibacterial properties of Zr-based metallic glasses surfaces. It is found that the self-organized microholes structure has the best effect in reducing the adhesion of bacteria on the surface of the material. [ABSTRACT FROM AUTHOR]

• Manufacturing AlCoCrFeNi high entropy alloy (HEA) reinforced by Fe-based metallic glass via selective laser melting (SLM). • The addition of metallic glass will lead to grain refinement. • Nanoindentation testing applied to the specimen. • Influence of the distribution of body-centered cubic (BCC) and face-centered cubic (FCC) phases on mechanical properties. • The reinforce of HEA by different added elements. The 5% Fe-based amorphous reinforced AlCoCrFeNi high-entropy alloy (HEA) specimens were prepared by selective laser melting (SLM) technique. The mixed of Fe-based amorphous reduces the grain diameter and eliminates the presence of texture. Meanwhile, the anisotropy of the specimen was reduced. The addition of Fe-based amorphous causes the precipitation of FCC phase in the body-centered cubic (BCC) matrix, and the face-centered cubic (FCC) phase is uniformly distributed at the grain boundaries. The presence of FCC phase significantly reduces the internal stress of the specimen. The elements in the amorphous alloy solidly dissolve into the BCC matrix during the printing process, further strengthening the BCC matrix. The residual amorphous and nanocrystalline phases also result in a significant improvement in the performance of the specimen. [ABSTRACT FROM AUTHOR]

• FeCoCrNiMoSi x (x = 0.5, 1.0, 1.5) HEAs were fabricated by SPS under 1150 °C. • Hardness of FeCoCrNiMoSi 1.5 reached 1186 HV. • High corrosion potential of Si makes FeCoCrNiMoSi 1.5 exhibits great corrosion resistance. • The oxidation properties FeCoCrNiMoSi 0.5 were greater than that of other FeCoCrNiMo HEAs. • Different properties can be obtained through controlling Si content. FeCoCrNiMoSi x (x = 0.5, 1.0, 1.5) high-entropy alloys (HEAs) were successfully fabricated by spark plasma sintering (SPS). The microstructure, tribological properties, oxidation behaviors and corrosion resistance of the HEAs were systematically investigated. The experimental results showed that the microstructure mainly consisted of Fe-rich face-centered-cubic (FCC) phase, Mo-rich FCC phase solid solution and various Si-rich intermetallics, where the elevated Si content coarsened the primary Mo-rich phase into dendritic eventually. These Mo-rich dendrites possessed strong covalent-dominant atomic bonds that enhanced the microhardness (from 725 to 1186 HV) and wear resistance. The FeCoCrNiMoSi 0.5 HEA exhibited an outstanding combination of relatively high wear resistance and the strongest oxidation resistance under 800 °C among the three alloy compositions. The corrosion resistance of HEAs showed an increasing trend with the elevated Si content, and FeCoCrNiMoSi 1.5 presented the best performance. [ABSTRACT FROM AUTHOR]

• We control the size of powder particle size as a variable to conduct a study on RAFM steel supplemented by LMD technology for the first time. • The laser additive process was monitored by high-speed photography. The length of the molten pool and the solidification rate are studied, and the formation process of the pores is explained microscopically. • The average grain size of LMD RAFM steel was further analyzed, and a reasonable explanation of its mechanical properties was given. • The change behavior of focal length of coaxial feeding powder particle size was studied. Laser melting deposition (LMD) is a promising way for the fabrication of complex reduced activation ferritic/martensitic (RAFM) steel components which provides an exceptional opportunity to improve the existing designs and move toward fabricating fine features and complex geometries with higher efficiencies. It is well known that if steel members are welded together, defects will be concentrated in the welded joint. We can control the scanning path of the laser to achieve a complex component molding, avoiding welding. Considering the LMD technology, the results of each layer of powder molding will affect the fineness of the final processed products, such as laser power, scanning speed, defocus and so on, which are all important factors affecting the products. We control the size of powder particle size as a variable to conduct a study on RAFM steel supplemented by LMD technology for the first time, and its microstructure and grain size were analyzed. In terms of mechanical properties, its hardness, Charpy impact, tensile strength and elongation were measured. The results show that compared with other processing processes including Selective Laser Melting (SLM), rolling, welding joints, the tensile strength of RAFM steel manufactured by laser coaxial powder feeding is up to 1057.75 MPa, and there are no pores and almost no defects when using small particle size powder. The microstructure of LMD RAFM steel contains a large amount of lath martensite and δ-ferrite, and some precipitates such as Mx, whose average grain size decreases with the increase of powder particle size (5–150 μm). In this study, the laser additive process was monitored by high-speed photography, and the average grain size of LMD RAFM steel was further analyzed, and a reasonable explanation of its mechanical properties was given. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tunable micro/nano-structured Ti surfaces were prepared by chemical treatments. • Macrophage spreading was highly dependent on nano-structure morphological features. • Micro/nano-structured Ti surfaces activated M2 phenotype in macrophages. Current understanding on the interactions between micro/nano-structured Ti surfaces and macrophages is still limited. In this work, TiO 2 nano-structures were introduced onto acid-etched Ti surfaces by alkali-heat treatment, ion exchange and subsequent heat treatment. By adjusting the concentration of NaOH during alkali-heat treatment, nano-flakes, nano-flakes mixed with nano-wires or nano-wires could formed on acid-etched Ti surfaces. The micro- and micro/nano-structured Ti surfaces possessed similar surface chemical and phase compositions. In vitro results indicate that the morphology of macrophages was highly dependent on the morphological features of nano-structures. Nano-flakes and nano-wires were favorable to induce the formation of lamellipodia and filopodia, respectively. Compared to micro-structured Ti surface, micro/nano-structured Ti surfaces polarized macrophages to their M2 phenotype and enhanced the gene expressions of osteogenic growth factors in macrophages. The M2 polarized macrophages promoted the maturation of osteoblasts. Compared to that with nano-flakes or nano-wires, the surface with mixed features of nano-flakes and nano-wires exhibited stronger anti-inflammatory and osteo-immunomodulatory effects. The findings presented in the current work suggest that introducing micro/nano-topographies onto Ti-based implant surfaces is a promising strategy to modulate the inflammatory response and mediate osteogenesis. [ABSTRACT FROM AUTHOR]

• AlSi10Mg components were fabricated by SLM under different VED ranges, i.e. conduction, transitional, and keyhole modes. • The KDP was consisted of α-Al, with less than 15 μm grain size, and enclosed by ~200 nm eutectic Si cellular networks. • No preferential crystallographic orientation could be observed within the KDP. • The high-stress exponents indicate that the creep behavior is controlled by dislocation-particle interactions. • The SLM AlSi10Mg fabricated in the transition mode exhibits a high tensile strength combined with reasonable ductility. The effect of the volumetric energy density (VED) on the keyhole formation, microstructural evolution and associated mechanical properties of AlSi10Mg fabricated by selective laser melting (SLM) has been systematically investigated. The results indicated that three melting modes could be distinguished during the laser melting process, corresponding to different VED ranges, i.e. conduction mode (<50 J mm-3), transitional mode (~50–65 J mm-3), and keyhole mode (>65 J mm-3). A high VED not only produced keyhole defects and hydrogen pores, but also generated two types of molten pool, i.e. a general shallow molten pool (GSP) and a keyhole-induced deep molten pool (KDP). The GSP was mainly consisted of an α-Al matrix, with ~30 µm grains size, and enclosed by a ~500 nm eutectic Si cellular network. The grain size of the KDP was less than 15 µm, and it has both a finer Si network (~200 nm) and nano-scale Si particles. No preferential crystallographic orientation could be observed within the KDP, while a strong texture along<111>orientation was exhibited in the GSP. These were responsible for the different mechanical properties of the SLM parts under different melting modes. The related mechanisms of the GSP and the KDP formation are comprehensively discussed and a correlation between the microstructure and the mechanical properties is also outlined. [ABSTRACT FROM AUTHOR]

• According to the characteristics of pulsed laser, the application of pulsed laser in alloy welding was summarized. • By discussing the crack sensitivity criterion, the mechanism of pulse laser welding to solve welding crack was analyzed. • The outlook for the future trends of pulsed laser welding and crack criterion was presented. There are mainly two kinds of laser used in welding of materials, continuous laser beam welding (CLBW) and pulsed laser beam welding (PLBW). The two kinds of laser welding have each welding characteristics. Compared with CLBW, the heat input of PLBW can be controlled lower, and has been widely used in the connection of thin plate materials. Since the pulse shaping can be edited to realize the preheating and slow cooling of each welding process, pulsed laser has been studied to suppress hot cracks and other defects in the field of aluminum alloy, magnesium alloy and other materials welding. This article describes the application of pulsed laser in alloy welding. The main welding problems and prevention methods were summarized. By discussing the index had been proposed to predict the sensitivity of solidification cracks, the formation and growth processes of hot cracks in pulsed laser welding was more comprehensively analyzed. Finally, the outlook for the future trends of pulsed laser welding is presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced Al alloy-polymer friction stir welding joints via laser ablation pre-treatment. • The large mechanical interlocking of joints was attributed to the grooves with geometry characteristic. • The formation of C–O–Al bond enhanced the interfacial bonding. In this work, a micro-texture through laser ablation pre-treatment on aluminum alloy surface was designed, which successfully induced high bonding strength of aluminum alloy-polymer friction stir welding joints. The bonding mechanism of aluminum alloy-polymer was attributed to the large mechanical interlocking from the geometric grooves in micro-textures and the formation of C–O–Al bond at the interfaces. This study provides new insight of friction stir welding of metal and polymer through controllable surface pre-treatments. [ABSTRACT FROM AUTHOR]

H13 steel is often damaged by wear, erosion, and thermal fatigue. It is one of the essential methods to improve the service life of H13 steel by preparing a coating on it. Due to the advantages of high melting point, good wear, and corrosion resistance of Mo, Mo coating was fabricated on H13 steel by electro spark deposition (ESD) process in this study. The influences of the depositing parameters (deposition power, discharge frequency, and specific deposition time) on the roughness of the coating, thickness, and properties were investigated in detail. The optimized depositing parameters were obtained by comparing roughness, thickness, and crack performance of the coating. The results show that the cross-section of the coating mainly consisted of strengthening zone and transition zone. Metallurgical bonding was formed between the coating and substrate. The Mo coating mainly consisted of Fe9.7Mo0.3, Fe-Cr, FeMo, and Fe2Mo cemented carbide phases, and an amorphous phase. The Mo coating had better microhardness, wear, and corrosion resistance than substrate, which could significantly improve the service life of the H13 steel. [ABSTRACT FROM AUTHOR]

Crack-free samples were made from Nb nanoparticles modified Ni60 hard-facing alloy using laser metal deposition. Addition of Nb nanoparticles was carried out to modify the columnar dendrites and eutectic microstructures by providing large number of nucleation sites. The purpose of this study was to evaluate the effect of nanoparticles addition on cracking susceptibility of Ni–Cr–B–Si alloy. The results show that with addition of Nb nanoparticles, the cracking susceptibility reduced significantly with acceptable hardness loss. Large hard phases were refined and the columnar dendrites were converted to equiaxed grains, leading to a separated eutectic microstructure which restrain the initiation and growth of cracks. The study demonstrated a new method to tackle the cracking problem of laser manufactured Ni–Cr–B–Si alloys, accelerating the adoption of Ni–Cr–B–Si alloys on additive manufacturing applications. [ABSTRACT FROM AUTHOR]

Eight Al 16.80 Co 20.74 Cr 20.49 Fe 21.28 Ni 20.70 high entropy alloy (HEA) coatings were fabricated by laser cladding with different laser scanning speed. The mechanical properties caused by phase transformation and microstructure evolution of Al 16.80 Co 20.74 Cr 20.49 Fe 21.28 Ni 20.70 HEA coatings were investigated. The experimental results showed that the volume fraction of the FCC phase and the BCC phase in each coating were different depending on laser scanning speed. High laser scanning speed will increase the number of BCC phase. BCC phase was composed of alternate A2 and B2 structure formed by spinodal decomposition. All coatings exhibited a polycrystalline structure composed of uniform equiaxed grains. The grain size of equiaxed grains reduced from 185 to 42 µm with increased laser scanning speed. The phase-mechanical properties connection at nano-scale were established by nano-hardness mapping and elastic modulus mapping. Furthermore, the micromechanical properties of individual FCC phase and BCC phase were studied by analyzing nanoindentation data statistically. The BCC phases were found to have a higher nano-hardness and elastic modulus than the FCC phases. Therefore, the increment of the BCC phase could significantly enhance the strength and wear resistance of coatings. The optimum wear resistance was obtained in V17, owning a higher volume fraction of BCC (>90%) and finer grains (75 µm). In addition, the strengthening mechanism has been discussed. Grain boundary strengthening makes a great contribution to the excellent performance of coatings. • The volume fraction and morphology of the FCC phase and BCC phase vary as the increase of the laser scanning speed. • Nano-hardness mapping and elastic modulus mapping can evaluate the difference of mechanical properties in nano-scale. • The difference in mechanical properties of FCC phase and BCC phase in the HEA coating were analyzed. • The increment of the BCC phase could significantly enhance the strength and wear resistance of coatings. [ABSTRACT FROM AUTHOR]

• Ramp-down and step-down pulse shaping were designed to suppress 5083 aluminum alloy cracks. • Ramp-down pulses decrease the volume of liquid molten pool at the end of the laser process. • Tailing pulses increase the temperature gradient of the solidification process and reduce the vulnerable zone length. • The effect of pulse shaping on crack suppression in vertical direction is more obvious than that in horizontal direction. Solidification crack was a common welding defect in welding of aluminum alloy. When solidification shrinkage and heat shrinkage of the vulnerable zone and its surrounding solids were hindered, it will cause grain boundary cracking owing to insufficient supply of liquid metal. Therefore, cracks generally appear in the middle part of aluminum alloy welding spot at the late stage of solidification. Compared with continuous laser, pulsed laser could meet more precise heat input control and was widely used in aluminum alloy sheet welding. In this research, by designing different pulse shaping to improve the solidification condition of the 5083 aluminum alloy pulsed laser welding spot, the numerical simulation was used for analyzing the solidification rate and temperature gradient of molten pool. Application of ramp-down pulse decreased crack cross-sectional area from 420475 µm2 to 0, and step-down pulse could also effectively control the crack radius. The results showed that effect of suppressing solidification crack on the horizontal direction of the welding spot was obvious to the vertical direction. Using ramp-down or step-down pulse shaping also reduced the volume of the liquid molten pool at the end of the laser process, which decreased the shrinkage stress at the late stage of solidification. [ABSTRACT FROM AUTHOR]

Iron-based amorphous alloys have received extensive attention due to their high hardness, elastic modulus/limit and wear/corrosion resistance. In this research, an attempt has been made to develop an amorphous coating of Fe-Cr-Mo-C-B-Y metallic glass coating on the steel substrate through laser surface treatment. During the test, various process parameters are used to determine the position of the amorphous phase. After coating, the microstructure and phase distribution of the coating were analyzed by scanning electron microscope, X-ray diffraction and transmission electron microscope. Mechanical properties of the coating were analyzed by using microhardness testing, abrasion resistance and nanoindentation methods. The results show that the coating thickness varies directly with the incident laser power and interaction time. The microstructure of the coating can be divided into three layers: the first layer (columnar crystals), the second layer (the crystalline phase filled with the unit structure) and the third layer (the unit structure consists of a crystalline phase and an amorphous phase). As the heat input of laser cladding decreases, the volume fraction of the amorphous phase increases, and the average microhardness and nanohardness increase. • A new phase between the amorphous structure and the amorphous equiaxed composite structure was found. • M 23 C 6 (M = Fe, Cr, Mo), γ-(Fe, Cr, Mo) and bcc-Fe phases were found in the coating. • Bcc-Fe phase can effectively increase the plasticity of the coating. [ABSTRACT FROM AUTHOR]

High-speed laser cladding technology can significantly improve the efficiency of coating preparation and effectively widen the application range of laser cladding. In this study, the Ni45 powders were deposited on steel substrate by traditional low speed laser cladding and high-speed laser cladding process, respectively. The cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high-speed laser cladded Ni45 alloy coatings were compared. It can be seen that the thickness of the high-speed laser cladding coating was much thinner than that of the traditional laser cladding coating. Compared with traditional laser cladding, high-speed laser cladding could achieve a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm2/min. The microstructure of the two kinds of coatings shows the same growth law, but the microstructure in high-speed laser cladding was smaller and denser, and the columnar crystal interval was narrower, only about 6 μm. It is found that the cooling rate of the traditional laser cladding coating was smaller than that of the high-speed laser cladding, and as the cladding speed increased, the cooling rate became higher and higher. The cross-section microhardness of the traditional laser cladding coating was relatively uniform of 337 HV 0.2 , while the microhardness of high-speed laser cladding surface increased to about 543 HV 0.2. In addition, the wear and corrosion resistance of high-speed laser cladded coatings were better than that of traditional laser cladded coatings. As the cladding speed increased, the wear and corrosion resistance of the cladded coatings became better. • High-speed laser cladding coating had low roughness and thin coating. • The cooling rate increased exponentially with a decrease of secondary dendrite arm. • The wear and corrosion resistance increased with the increase of cladding speed. • The microstructure was refined continuously with the increase of cladding speed. [ABSTRACT FROM AUTHOR]

• The variable butt gap is used to study the gap bridging ability of laser-MIG arc hybrid welding. • Developed the welding process of laser-MIG arc hybrid welding under larger butt gap. • Laser-arc distance affects weld formation by affecting arc parameters and droplet transition. • Droplet transition is a mixture of short circuit transition and liquid bridge transition. At present, there are few researches on laser -MIG arc hybrid welding with a large butt gap. In this paper, laser-MIG arc hybrid welding is used to weld low-alloy high-strength steel with a thickness of 3 mm, and a laser-MIG arc hybrid welding process under large gap conditions is developed. This paper studies the effects of arc voltage, laser-wire distance, and wire feed speed on the gap bridging capability of hybrid welding under different butting gaps. Under the condition of the 1 mm butt gap, the influence mechanism of laser-wire distance on weld the weld formation of hybrid welding is analyzed by combining high-speed photography, welding current and voltage waveform, the macroscopic and microscopic morphology of the weld. The results show that there are optimal process parameter values for the effects of arc voltage and laser-wire distance on the gap bridging capability of hybrid welding. Adjusting the laser-wire distance can optimize the energy distribution of laser on the welding wire and weld pool, thus controlling the arc current, voltage, and droplet transition mode, and finally affecting the weld penetration and forming. When the laser-wire distance is 0 mm, the droplet transition frequency is the fastest, and the droplet transition is a mixture of short circuit transition and liquid bridge transition. At this point, the welding rate is the fastest and the welding process is the most stable. However, by comprehensively integrating factors such as the gap bridging capability and the weld penetration, the optimal processing parameters are obtained when the laser-wire distance is 0.5 mm. [ABSTRACT FROM AUTHOR]

Stellite 12 and Ti/B 4 C composite coatings were successfully fabricated on the surface of 304 stainless steel substrates by laser cladding. The effect of Ti/B 4 C with different mass fractions on the structure and properties of Stellite 12 coating were studied. The properties and the growth mode of the coating were analyzed. The results show that the Stellite 12 coating was mainly composed of face-centered cubic γ-Co and Cr 7 C 3. With the addition of Ti/B 4 C, TiC submicron particle phase was synthesized in situ in the coatings. Residual B 4 C as a heterogeneous nucleus particle, forming a submicron microstructure TiC/B 4 C strengthening phase, and the particle size gradually decreases. The TiC/B 4 C particles can refine the grains of the coatings. The micro-hardness of the coating gradually increased with the increase of Ti/B 4 C, and the highest were 650 HV. The wear resistance and oxidation resistance of the coatings gradually increased with the increase of Ti/B 4 C. • After doping, the coating performance was significantly improved. • TiC generated in situ made the coating grains to reach the sub-micron level. • The presence of TiO 2 oxide layer greatly improved the oxidation resistance of the coatings. [ABSTRACT FROM AUTHOR]