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C f @PyC/SiC composites, using needle-punched preforms, 3D orthogonal woven preforms and 3D 4-step braided preforms (braiding angles of 10°, 20° and 30°) as the reinforcement, were obtained through chemical vapor infiltration (CVI) method. The tensile strength before and after oxidation of the composites were investigated, and the microstructure, appearance of fracture and phase component of the composites were also analyzed. The results show that the mechanical properties and oxidation resistance of composites are greatly affected by the preform structures. The tensile strengths of 3D 4-step braided composites with the braiding angle of 10° are the best among all composites before and after oxidation, which are 266.40 ± 16.98 MPa and 238.66 ± 14.98 MPa. Before oxidation, the fibers and matrix at the fracture of 3D 4-step braided composites are in staggered distribution. The mechanical enhancement mechanisms of composites such as crack deflection, interface debonding and fiber pull-out, were beneficial to good performance and excellent mechanical properties. After oxidation, the deflection and branching effects of the interface on the crack are not fully manifested, and enhancement and toughening mechanisms are not fully played due to the oxidation of the carbon fiber and the PyC interface. • C f @PyC/SiC composites with five structure preforms were prepared by CVI method. • The tensile strength of 3D 4-step braided composites with braiding angle of 10° is the highest. • The tensile strength retention rate of 3D 4-step braided composites is around 90 %. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) manufactures components through the overlapping of multi-track and multi-layer molten pools of metal powders, resulting in two types of molten pool boundaries (MPBs), "layer-layer" and "track-track" MPBs, remaining in SLM parts. The microstructure of MPBs exhibits a complex and regular spatial topological structure. There is a coarse grain zone below the MPBs and nonmetallic elements (C, O, Si) near the MPBs are in an unstable state. Long and thin columnar grains with the same orientations distribute on two sides of the "layer-layer" MPBs, whereas the columnar grains on both sides of "track-track" MPBs have different orientations. The "track-track" MPBs are short and intersect with "layer-layer" MPBs at some points and form acute angles, where cracks are initiated when applied with external loads. The effect of the MPBs on microscopic slipping, macroscopic ductility and fracture mechanism of the SLM parts made along different directions, which were exerted a tensile loading in the as-built condition without heat treatment, was analyzed and evaluated using slip theory and experiments. The results reveal that the MPBs have a significant impact on the microscopic slipping at the loading, macroscopic plastic behavior and fracture mode, and are one of the main reasons for the obvious anisotropy and low ductility of SLM parts. [ABSTRACT FROM AUTHOR]

Multifunctional intrinsic self-healing polymers (ISP) are gaining increasing attention these days, and many studies have been devoted to solving the conflict between achieving high mechanical polymer strength and active polymer chain diffusion. In this research, we developed an optimized self-healing composite coating by adding Benzotriazole (BTA) loaded nano silica (SiO 2 @BTA) to a dynamic cross-linked Polydimethylsiloxane (PDMS) network，which allows substantial and fast healing of the material integrity upon damage due to the hydrogen interaction between urea and BTA. BTA leaching tests demonstrated a longer release profile during the coating service life and corrosion tests in a 3.5 wt% NaCl aqueous solution indicated that the SiO 2 @BTA modified PDMS coating shows enhanced corrosion protection of carbon steel upon coating damage. Moreover, after addition of SiO 2 @BTA, the material failure strength increased from ~1.5 MPa to ~5.5 MPa, and the healing efficiency increased from ~59% to ~90% for 24 h healing at room temperature. Above all, this research provides an intrinsic self-healing coating design method to improve the mechanical strength and the self-healing ability of the ISP as well as enhancing the coating's corrosion protection ability. [Display omitted] • Self-healing coatings were obtained by adding SiO 2 @BTA to reversibly silicone matrix. • Interaction between urea and BTA accounts for the optimized self-healing process. • Mechanical strength and self-healing property can be improved simultaneously. • The coating exhibits effective corrosion protection ability upon mechanical damage. [ABSTRACT FROM AUTHOR]

To predict oxidative damage of interfaces and fibers under high temperature aerobic environment and mechanical strength of composites before and after oxidation, oxygen permeation mass transfer modeling and onion-like micromechanical modeling of multilayered interface were proposed. The oxygen mass transfer theory and oxidation damage theory of PyC interface were used to establish the two models. The oxidative damage of PyC interface was extended to (PyC-SiC) n multilayered interface, and transformation of SiC phase and microcracks caused by thermal mismatch were also considered. The law of oxygen permeation mass transfer and the evolution of fiber oxidative damage in the "Carbon fiber/(PyC-SiC) n multilayered interface" region were revealed. The mechanical strength of composites under different interface layers was researched, resembling an onion-like wrapping in layers from the core outwards. Furthermore, C f @(PyC-SiC) n /SiC(n = 1/2/3/4) composites were prepared by chemical vapor infiltration (CVI) method. The mechanical properties of the composites were tested before and after oxidation. A comparison was made between the experimental and predicted tensile strengths before and after oxidation. The predicted results of tensile strength were found to be in good agreement with the experimental ones. In addition, the results show that PyC-SiC multilayered interface has a positive effect on the tensile strength of the composites, mainly as the cracks are deflected and branched by the multilayered interface to promote the multistage pull-out of the fibers. With the increase of interface number, the oxygen diffusion path was lengthened and zigzagged, reducing the oxidative damage of fiber and interface. [ABSTRACT FROM AUTHOR]

Amphiphilic block copolymer (PTFEMA- co -PSBMA) functionalized silica (SiO 2) nanoparticles of SiO 2 - g -(PTFEMA- co -PSBMA) were prepared by empolying surface-initiated atom transfer radical polymerization (SI-ATRP) technique. Then the SiO 2 -g-(PTFEMA- co -PSBMA) nanoparticles are physically blended with polydimethylsiloxane (PDMS) matrix to prepare one kind of novel fouling release antifouling coating. • Preparation of a new type of functional silica nanoparticle (SiO 2 - g -(PTFEMA- co -PSBMA)). • SiO 2 - g -(PTFEMA- co -PSBMA) and PDMS can be physically blended to prepare a functional antifouling coating. • The functional antifouling coating exhibits excellent antifouling performance along with good fouling release performance. • The functional antifouling coating can still maintain good antifouling performance even if it suffers heavy surface wear. Ocean-going ships, deep-sea equipment, coastal facilities, and other underwater surfaces are often attached to and fouled by marine microorganisms, animals, and plants, leading to damage, equipment failure or major economic losses in severe cases. Therefore, it is of great significance to take measures to prevent marine biofouling. To date, no single eco-friendly technology has been developed to achieve good antifouling effects. Therefore, the combination of multiple antifouling factors is still one of the main strategies to strengthen antibiofouling performance. In this paper, amphiphilic block copolymer (PTFEMA- co -PSBMA) functionalized silica (SiO 2) nanoparticles of SiO 2 - g -(PTFEMA- co -PSBMA) were prepared by surface initiated atom transfer radical polymerization (SI-ATRP), and then they were physically blended with polydimethylsiloxane (PDMS) matrix to prepare one kind of novel antifouling coating. Compared with control silicone rubber coating and bare SiO 2 -dopped silicone rubber coating, the experiment results show that the diatom density on the surface of the copolymer functionalized silica nanoparticle-dopped coating is reduced by approximately 30 % and 50 %, respectively. Furthermore, upon employing washing process, it is found that the highest removal rate of diatoms on the surface of the copolymer functionalized silica nanoparticle coating is 50 %, which is approximately twice the removal rate of the unmodified SiO 2 silicone rubber coating. Finally, it is found that the surface of the copolymer functionalized silica nanoparticle coating still has good antifouling and fouling release properties upon encountering wear test. These above results prove that the coatings with functionalized nanosilica nanoparticles have better antifouling performance. Current strategy in this work provides a new route for developing environmentally friendly fouling-releasing antifouling coatings. [ABSTRACT FROM AUTHOR]

• NiTi shape memory alloys with different Ni atomic percentages were formed by L-PBF. • Ni content affected the Ms temperature and phase composition of L-PBF NiTi alloy. • An atomic percentages phase transition temperature equation was proposed firstly. • L-PBF NiTi alloy showed SME with lower Ni content, otherwise superelasticity. In this study, three NiTi shape memory alloys with different Ni atomic percentage (50.73, 50.93 and 51.27 at%) were fabricated by laser powder bed fusion (L-PBF). The effect of Ni content on phase transformation temperature, phase composition, microstructure, mechanical properties and deformation recovery phenomenon of NiTi alloy were systematically investigated. The results indicated that the Ni content of L-PBF NiTi alloy affected Ms temperature and further affected phase composition. According to the effect of Ni contents on phase transition temperatures, a relationship between them was fitted. Subsequently, an equation defining the atomic percentage phase transition temperature is proposed. The effect of Ni content on grain orientation, texture and grain size was limited, but it had an effect on hardness and compression performance. L-PBF NiTi sample displayed shape memory effect with the lower Ni content (50.73 at%), however, showed superelasticity phenomenon with the higher Ni content (50.93 and 51.27 at%). Therefore, transformation temperature and deformation recovery phenomenon of L-PBF NiTi alloy could be tailored by adjusting Ni content to achieve special applications in the future. [ABSTRACT FROM AUTHOR]

• It studied the effect of TiC on microstructure and mechanical property of SLM Al. • An ultrafine eutectic microstructure was observed in the spherical Al matrix. • Solubility reduced and network microstructure became coarser with TiC increasing. • Al-15Si/1% TiC has high property due to particle reinforcement and ring structure. Selective laser melting (SLM) has been regarded as one of the most effective powder-based additive manufacturing (AM) methods for metal parts. The present study systematically investigated the influence of adding TiC content on the microstructural evolution and mechanical property of SLM hypereutectic Al-15Si alloy. Due to the high cooling rate during the SLM process, an ultrafine eutectic microstructure was observed in the form of spherical sub-micro-sized network eutectic Si embedded in the Al matrix, resulting in high tensile properties (398 MPa, 2.6%) and micro-hardness (154 Hv) for Al-15Si alloy. The solubility of Si atom in the Al matrix was calculated to be 9.37 at%. With increasing the TiC content from 1.0, 2.5 to 10 wt%, the solubility decreased rapidly and the network eutectic microstructure became coarser, precipitating out some small Si particles finally. That was because the TiC addition changed the thermodynamics of the melt pool, especially changed the undercooling degree in the SLM process. Attributing to the effect of eutectic microstructural evolution and the particle reinforcement, the micro-hardness was down firstly (146 Hv) and then up (177 Hv). Inversely, the tensile property firstly rose (578 MPa 7.86%) then descended (313 MPa, 2.24%). This study indicated that the microstructure and mechanical properties of SLM Al-15Si alloy can be tailored by suitable addition of TiC content. [ABSTRACT FROM AUTHOR]

• Nano-TiB 2 reinforced S136 mould steel composites were fabricated by SLM. • Effects of TiB 2 on microstructures and corrosion property of composites were studied. • The SLM composites possessed finer grains compared to the SLM pure S136. • Higher electrochemical property and less weight loss was obtained for SLM composites. The S136 mould steel matrix with varying mass fractions of TiB 2 (0–2.5 wt%) were produced by selective laser melting (SLM). This study mainly focused on the influence of TiB 2 content on the microstructure and corrosion property of the S136 composites in detail. The electrochemical method and weight loss test in the 3.5 wt% NaCl solution and 6 wt% FeCl 3 solution were conducted to determine the corrosion resistance of the composites. Results demonstrated that the SLM 0.5 wt% TiB 2 /S136 composites possesses higher corrosion and pitting potentials as well as lower corrosion current density and weight loss compared to that of other samples owing to the existence of the finer grains and TiO 2 passive film. Furthermore, the corrosion property of the composites decreased with the gradually increasing TiB 2 content associating with more defects and galvanic cells, which was detrimental to the corrosion property. Herein, the corrosion mechanism of the SLM TiB 2 /S136 composites was also deeply discussed in this paper. [ABSTRACT FROM AUTHOR]

• Age of diagnosis, primary site, histology, tumor stage, use of surgery and tumor size were identified as independent prognostic factors for both overall and cancer-specific survival of chordoma patients. • The optimal age cutoff values of chordoma patients were 38, 54 and 66 years. • The optimal cutoff values of chordoma tumor size were identified as 2.9 and 10.0 cm. • The nomogram constructed in present study can serve as an effective and convenient evaluation tool to help surgeons to perform personalized survival evaluation and mortality risk identification in chordoma patients. The survival prediction of patients with chordoma is difficult to make due to the rarity of this oncologic disease. Our objective was to apply a nomogram to predict survival outcomes in individuals with chordoma of the skull base, vertebral column, and pelvis. A total of 558 patients with chordoma between 1973 and 2014 were collected from the Surveillance, Epidemiology, and End Results (SEER) database. Independent prognostic factors in patients with chordoma were identified via univariate and multivariate Cox analysis. Then these prognostic factors were incorporated into a nomogram to predict 3- and 5-year overall survival and cancer-specific survival rates. Internal and external data were used to validate the nomograms. Concordance indices (C-indices) were used to estimate the accuracy of this nomogram system. A total of 558 patients were randomly assigned into a training cohort (n = 372) and a validation cohort (n = 186). Age, surgical stage, tumor size, histology, primary site, and use of surgery were identified as independent prognostic factors via univariate and multivariate Cox analysis (all p < 0.05) and further included to establish the nomogram. The C-indices for overall survival and cancer-specific survival prediction of the training cohort were 0.775 (95% confidence interval, 0.770–0.779) and 0.756 (95% confidence interval, 0.749 –0.762). The calibration plots both showed an excellent consistency between actual survival and nomogram prediction. Nomograms were constructed to predict overall survival and cancer-specific survival for patients with chordoma of the skull base, vertebral column, and pelvis. The nomogram could help surgeons to identify high risk of mortality and evaluate prognosis in patients with chordoma. [ABSTRACT FROM AUTHOR]

In this work, a novel approach combining liquid deposition with selective laser melting (SLM) is used for fabricating reduced graphene oxide (RGO)/S136 metal matrix composites (MMCs). The grain sizes, crystallographic textures, phase compositions and mechanical properties can be tailored by controlling the RGO content in the RGO/S136 MMCs. The results show that the average grain size reaches its smallest size of 0.75 μm when 0.1 wt% RGO was added to the RGO/S136 MMCs. As the RGO content is increased from 0 wt% to 0.5 wt%, a continuous transition of the grains from the (001) orientation to the (101) and (111) orientations is observed. In addition, the cellular dendritic grains transform into equiaxed fine grains with increasing RGO content. The SLM-prepared RGO/S136 MMCs are dominated by high-angle grain boundaries (˃15°) and the martensite (bcc) phase. The hardness, ultimate tensile strength and yield strength of the SLM RGO/S136 MMCs exhibit trends that initially increase and then decrease, with maximum values of 580.6 HV, 535.3 MPa and 515.8 MPa, respectively. This paper highlights the possibility of controlling the RGO content to achieve the desired microstructural characteristics and mechanical properties of RGO/S136 MMCs fabricated by the SLM process. Unlabelled Image • The fully dense RGO/S136 composites via molecular-level mixing were firstly fabricated by selective laser melting. • EBSD patterns revealed the refined grain and tailored microstructure for SLM RGO/S136 composites. • SLM RGO/S136 composites with 0.1 wt% RGO exhibited maximum tensile properties and hardness. [ABSTRACT FROM AUTHOR]

• Laser-scan mode affects grain structure and texture types. • The unidirectional scanning mode promotes stronger texture in building direction. • Unidirectional scanned samples exhibit phase transformation under magnetic field. • The magnetic-field-induced strain in Ni-Mn-In samples can reach 820 ppm. Dense polycrystalline Ni-Mn-In alloy specimens were fabricated by utilizing two laser scanning strategies of laser powder bed fusion (L-PBF) technology for the first time. The effect of scanning strategies on the microstructure, crystals texture and magnetic-field-induced strain (MFIS) were investigated systematically. The results showed that the uniformly sized grains were formed in samples with unidirectional scanning strategy, while the bidirectional scanning strategy leads to a bimodal distribution of grains. The MFIS value in unidirectional strategy increased over twofold, rising from 403 ppm to 820 ppm. This work opens a new insight into regulating process parameters and customizing the microstructure and overall magnetic properties of Ni-Mn-In alloys in the additive manufacturing field. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced (SiC-ZrC) n multi-layer structural matrix composites were prepared by isothermal chemical vapor infiltration method. The microstructure, bending and ablation behavior of the composites with different number (n, n = 1, 2, 4) of SiC-ZrC layer were studied. The fracture morphology was step-like fracture. With the increase of n, the number of interfaces doubled, benefiting that the cracks kept deflecting and branching at the interface to consume lots of energy. The bending strength increased from 127.63 MPa (n = 1) to 276.85 MPa (n = 4). After ablation, among the prepared composites, C/(SiC-ZrC) 4 composite not only had the highest residual bending strength (169 MPa), but also had the best ablation resistance, which the mass and linear ablation rates were 1.17 ± 0.19 mg/s and 7.50 ± 0.56 µm/s, respectively. [ABSTRACT FROM AUTHOR]

The titanium alloy Ti–6Al–4V (TC4) and tungsten (W) possess excellent complementary properties that would be useful for a wide range of industrial applications if they could be suitably combined. Selective laser melting was applied to prepare TC4/W specimens with a bimetallic structure. A strong bond without interfacial macrocracks was obtained by adjusting the laser line energy density to <0.75 J/mm. The bond interface of the bimetallic structure reached a microhardness of 503 ± 20 HV, which was harder than that of the two base materials, and the transverse and longitudinal ultimate compressive strengths were 1510 ± 40 MPa at strains of 20%–22.5%. Three-point bending experiments showed that when TC4 was used as the base material, the flexural strength of the specimen was 2210.5 ± 44.5 MPa. The high strength of the bond interface was attributed to sufficient agitation of the molten pool and reinforcement by fine crystalline grains. The agitation was provided by the melting and elemental diffusion of TC4 owing to the high energy input during the formation of W, and the fine crystalline grains were obtained by the dispersed W particles providing multiple nucleation sites for liquid TC4. The bimetallic structure retained the strength of W and toughness of TC4, which bodes well for its industrial application. • Forming parameters affected bond strength of TC4/W bimetallic structure. • The forming of tungsten produced numerous fine β-phases at the bonded interface. • The microhardness of the interface of the TC4/W bimetallic structure reaches 503 HV. [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphene disperses well in aromatic petroleum resin by solution mixing. • Dispersibility of graphene in aromatic resin improved with xylene content decreased. • Graphene slows down the swelling ratio of aromatic resin immersed in water. • Graphene in aromatic petroleum resin can effectively shield corrosion factors. Graphene (Gr) uniformly dispersed aromatic petroleum resin (APR) coatings were prepared using exfoliated Gr and APR as raw materials by solution mixing method. Graphene was first mixed with the xylene solution and treated by ultrasonication. Then the APR was added to the mixture solution, after heating and stirring to remove the excess xylene solvent, the APR solution with uniform dispersion of graphene could be obtained. Atomic force microscopy (AFM) was used to test the thickness variation of the multilayer graphene layers before and after xylene adsorption. The results showed that the xylene which increased the thickness of the multilayer graphene was interspersed between the graphene layers. Raman spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) characterized that graphene obtained a good dispersion of Gr in APR. The electrochemical characteristics of graphene-modified APR coatings were tested by electrochemical impedance spectroscopy (EIS), and the results showed that the xylene content influenced the dispersion of graphene and flowability of the APR solution. The Gr/APR coatings with 45 wt% xylene exhibited the best corrosion protection performance. The impedance modulus of the coating in the low-frequency region after being immersed in 3.5 wt% sodium chloride solution for 100 days was greater than 109Ω·cm2. [ABSTRACT FROM AUTHOR]

• SiC f /HfC-SiC and SiC nws modified SiC f /HfC-SiC composites were prepared by PIP and CVI methods. • SiC nws were helpful to increase the pyrolysis yield rate of HfC precursor. • After impact-ablation, the flexural strength of SiC f /HfC-SiC reduced by 45.2 %; that of modified one only reduced by 30.9 %. SiC nanowires (SiC nws) modified SiC f /HfC-SiC composites were prepared by precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The microstructure, flexural strengths, impact and impact-ablation tests of the composites with and without SiC nws were investigated. The results showed that after introducing SiC nws , not only the retention rate of HfC ceramic produced by PIP was increased obviously, but also the fracture displacement of the modified composites was reduced due to the enhancement effect of SiC nws at interface between SiC fiber and matrix. After impact and impact-ablation, the strength retention of SiC nws modified composites was 91.6 % and 69.1 % respectively, higher than that of the composites without SiC nws (85.2 % and 54.8 %). As the impact resistance of the modified composites was improved by the pull-out and bridging of SiC nws , the ablation resistance of the impacted composites was enhanced as well. [ABSTRACT FROM AUTHOR]

To improve the reliability of C f /HfC-SiC composites after ablation, SiC fibers were used as reinforcement to replace carbon fibers. The composites were prepared by precursor infiltration and pyrolysis (PIP) and chemical vapor deposition (CVD) methods. The flexural properties of the cyclic ablated C f /HfC-SiC and SiC f /HfC-SiC composites were characterized. The results showed that the flexural strengths of C f /HfC-SiC and SiC f /HfC-SiC composites before ablation were 98.3 ± 6.8 and 108.5 ± 1.9 MPa, respectively. After three cycles of ablation, the flexural strengths of C f /HfC-SiC composites were 37.2 ± 2.4 MPa (decreased by about 62.2%), and the bending strengths of SiC f /HfC-SiC composites were 79.6 ± 4.3 MPa (only decreased by 26.6%). The high retention rate of the bending strength of SiC f /HfC-SiC composites was due to the protection of the complete oxide layer and good oxidation resistance of the SiC fiber. [ABSTRACT FROM AUTHOR]

In this study, Cu–Sn-based diamond composites were fabricated using L-PBF. The effects of the Cu-coated diamond on the melt-pool evolution, diamond–metal matrix bonding, thermal damage, and friction behavior of Cu in the Cu–Sn-based diamond composites were investigated. Moreover, the optimum L-PBF parameters for processing Cu-coated diamond/Cu–Sn composites were investigated. A convolutional neural network based on deep learning was used to process laser-scanned diamond images and evaluate the diamond thermal damage by model-feature visualization. The thermally damaged Cu-coated diamond and percentage of severely damaged parts were reduced compared to those of the uncoated diamond. Thick Cu coating changed the wettability of the diamond and matrix, thereby increasing the friction of the molten pool and unmelted metal particles and introducing the friction of the Cu microfluidic flow on the diamond. Hence, the mechanical holding force of the Cu Sn alloy matrix on the diamond substantially increased, and the bending strength of the Cu-coated diamond/Cu–Sn composites fabricated using L-PBF reached 720 MPa, which is approximately twice that of diamond/Cu–Sn (365 MPa). • Cu-coated diamond/Cu-Sn composite was formed by laser powder bed fusion. • The bending strength of Cu-coated diamond/Cu-Sn composites reached 720 MPa. • The thick Cu coatings improved the mechanical holding force on the diamond. • Laser-scanned-diamond prongs were susceptible to thermal damage. [ABSTRACT FROM AUTHOR]

A composite coating was developed to address the issues of low binding force and poor wear resistance of the hydroxyapatite coating on the surface of magnesium alloy. The composite coating, known as (C-HA) SiCnws coating, was prepared on the surface of AZ31 magnesium alloy using the carbonation-oxidation method of phenolic resin and electrophoretic deposition. The (C-HA) SiCnws coating is composed of a carbon coating as the middle layer, a hydroxyapatite coating as the surface layer, and SiC nanowires that connect the carbon layer and the HA coating. The morphology and infrared spectrum of the coating were characterized, and tests were conducted to evaluate the adhesion, wear performance, electrochemical properties, and corrosion resistance of the coating. The results demonstrate that the (C-HA) SiCnws coating is uniform and flat. The adhesion of the coating, as determined by tensile, is 3.51 ± 0.54 MPa, which is 88 % higher than that of the pure HA coating. Furthermore, the wear performance of the (C-HA) SiCnws coating is excellent, with a wear rate of only 0.96 × 10−3 mm3/(N·m), representing a reduction of 68.2 %. Additionally, the (C-HA) SiCnws coating demonstrates a favorable corrosion protection effect in both electrochemical polarization and corrosion tests. Overall, the prepared (C-HA) SiCnws coating exhibits significant enhancements in terms of adhesion, wear resistance, and corrosion resistance. • The SiCnws and HA particles are uniformly and organically bonded together. • The oxidation of the C coating leads to the extension of SiCnws within the coating. • Adhesion, wear resistance and corrosion resistance are greatly improved. [ABSTRACT FROM AUTHOR]

Purpose: In the implementation of large-size additive manufacturing (AM), the large printing area can be established by using the tiled and fixed multiple printing heads or the single dynamic printing head moving in the x–y plane, which requires a layer decomposition after the mesh slicing to generate segmented infill areas. The data processing flow of these schemes is redundant and inefficient to some extent, especially for the processing of complex stereolithograph (STL) models. It is of great importance in improving the overall efficiency of large-size AM technics software by simplifying the redundant steps. This paper aims to address these issues. Design/methodology/approach: In this paper, a method of directly generating segmented layered infill areas is proposed for AM. Initially, a vertices–mesh hybrid representation of STL models is constructed based on a divide-and-conquer strategy. Then, a trimming–mapping procedure is performed on sliced contours acquired from partial surfaces. Finally, to link trimmed open contours and inside-signal square corners as segmented infill areas, a region-based open contour closing algorithm is carried out in virtue of the developed data structures. Findings: In virtue of the proposed approach, the segmented layered infill areas can be directly generated from STL models. Experimental results indicate that the approach brings us the good property of efficiency, especially for complex STL models. Practical implications: The proposed approach can generate segmented layered infill areas efficiently in some cases. Originality/value: The region-based layered infill area generation approach discussed here will be a supplement to current data process technologies in large-size AM, which is very suitable for parallel processing and enables us to improve the efficiency of large-size AM technics software. [ABSTRACT FROM AUTHOR]

• C f /HfC and C f @PyC/HfC composites were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. • The results of thermal cyclic ablation and three-point bending tests show that after three time ablation cycles, the flexural strength of C f /HfC samples reduced by 63%; the flexural strength of C f @PyC/HfC samples only reduced by 36%. • The differences of cyclic ablation behaviour and flexural strength of C f /HfC and C f @PyC/HfC are attributed to the crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface. Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface. [ABSTRACT FROM AUTHOR]

Triply Periodic Minimal Surface (TPMS) porous structures are recognized as the most promising bionic artificial structures for tissue engineering. The fatigue properties of additive manufactured porous structures are essential for long-term use in a dynamical bio-skeletal environment. The aim of this study is to study the compression–compression fatigue behaviour and the underlying fatigue mechanism of Gyroid cellular structures (GCS), a typical TPMS porous structure. The high-cycle fatigue results show that both cyclic ratcheting and fatigue damage phenomena contribute to the failure of GCS during fatigue testing. For most fatigue loading stress, the failure samples have nearly 45° fracture bands along the diagonal surface. The fatigue ratio of GCS reaches 0.35 for as-built samples and can be raised to 0.45 after sandblasting treatment. The fatigue ratio values are higher than most of the other bending-dominated lattice structures, suggesting superior fatigue resistance properties of GCSs due to the smooth surface connection between struts. Besides, a systematic investigation of the crack initiation and propagation was conducted by both deformation analysis and finite element method to support experimental phenomena. The results also indicate that the fatigue resistance properties of GCSs are significantly enhanced by sandblasting post-treatment, through removing the adhered powder particles, inducing compressive residual stress on the surface and generating a nanocrystalline zone. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) coatings doped with different contents of SiC nanowire (SiCnws) were prepared on the surface of AZ31 magnesium alloy by electrophoretic deposition to solve the problems of low adhesion and poor wear resistance of pure HA coatings. Performance tests were conducted on the coating, including corrosion resistance, adhesion and wear performance. The results showed that the prepared coating was intact. The adhesion and wear resistance of the coating were significantly improved when the doping amount of SiCnws was 3%. Among them, the adhesion increased by 37.06% and the scratch depth decreased by 86.67%. At the same time, the corrosion resistance of the coating still maintained a high level. It showed that the performance of doping 3% SiCnws modified coating was balanced and excellent in all aspects. [Display omitted] • HA-SiCnws composite coating is prepared on AZ31 magnesium alloy. • The SiCnws and HA particles are uniformly and organically bonded together. • Adhesion and wear resistance are greatly improved. [ABSTRACT FROM AUTHOR]

Abstract The Cu-13.5Al-4Ni-0.5Ti copper-based shape memory alloys (SMAs) were fabricated by selective laser melting (SLM). The parameters were optimized to obtain almost fully dense copper-based SMAs samples. The phases and microstructures were characterized and the tensile properties at room temperature and 200 °C were evaluated. The XRD results showed that only the β 1 ′ phase could be detected in the Cu-based SMAs, which was attributed to the extremely short solidification time for the precipitation of α and γ 2 phases during SLM process. The grains were well refined and the average grain size was approximate 43 μm, which was much smaller than that of the cast copper-based SMAs. The X-phase (Cu 2 TiAl) is observed, which is granular and size 20–50 nm. The Cu-13.5Al-4Ni-0.5Ti copper-based SMAs fabricated by SLM exhibited excellent mechanical properties at room temperature, which was higher than that of the cast copper-based SMAs. This is attributed to two aspects: (1) grain refinement, (2) suppress of brittle γ 2 phase. Remarkably, the tensile test results at 200 °C showed both higher strength and elongation, which is attributed to the bcc structure of the parent phase and the stress-induced martensitic transformation at 200 °C. Meanwhile, the difference of microstructures and properties between SLM-fabricated Cu-based SMAs and casting Cu-based SMAs were analyzed and discussed in detail. Graphical abstract Image 1 Highlights • Near fully density Cu-13.5Al-4Ni-0.5Ti SMA is successfully fabricated. • β 1 ′ martensite and X phases are emerged in SLM-fabricated Cu-13.5Al-4Ni-0.5Ti. • The grain size of Cu-13.5Al-4Ni-0.5Ti alloy is smaller than cast counterparts. • The SLM-fabricated Cu-13.5Al-4Ni-0.5Ti SMA shows superior mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract Selective Laser Sintering (SLS) is one of the most mature and engineered polymeric 3D printing technologies, and the produced part is characterized by homogeneous polymorphism, which make the sintered material possess an ordered crystalline phase distribution and thus present a self-formed composite structure. This is due in large part to the special processing method during the SLS process. However, molecular motion mechanism between different phases remain unclear and further exploration is needed. Therefore, this paper firstly investigates the molecular motion mechanism concerning special composite phase structure of SLS-processed PA6 based on 2D correlation fourier transform mid-infrared (FT-MIR) spectra. The results show that although the crystal structure of the LT-α phase is less-ordered, the groups in LT-α change later than those in HT-α as the temperature increases. The overall movement sequence is: HT-α ˃ interphase ˃ LT-α, and the motion mode in the individual phase is the skeleton movement of carbon chains driven by H-bonds whereas the movement of interphase H-bonds is driven by the synergistic effect of the chain in HT-α. Besides, the symmetric methylene (v s (CH 2)) vibrates firstly both for HT-α and LT-α, and then is the stretching vibration of asymmetric methylene (v a s (CH 2)). Graphical abstract Image 104391 Highlights • This paper firstly investigates the composite phase structure of 3D-printed PA6 based on 2D correlation FT-MIR spectra. • The assignments of laser sintered PA6 concerning HT-α, interphase and LT-α were firstly presented. • The H-bonds in the interphase are mainly linked to the carbon skeletal chain of HT-α spherulites rather than LT-α. • The overall movement sequence of molecular chain is: HT-α ˃ interphase ˃ LT-α. • The v s (CH 2) vibrates firstly both for HT-α and LT-α, and then is the stretching vibration of v a s (CH 2). [ABSTRACT FROM AUTHOR]

Abstract A novel approach of liquid deposition method (LDM) together with selective laser melting (SLM) have been used to process Ti-43.5Al-6.5Nb-2Cr-0.5B/reduced graphene oxide (RGO) metal matrix composites (MMCs). The grain size, crystallography texture, phases composition and compressive properties can be tailored by controlling the RGO content in Ti-43.5Al-6.5Nb-2Cr-0.5B/RGO MMCs. Due to the combined effects of grain refinement mechanism and special phases composition, the SLM-processed TiAl/RGO parts exhibit the superior compressive strength of 1546.88 MPa and strain of 5.34%, as compare to the unreinforced Ti-43.5Al-6.5Nb-2Cr-0.5B counterpart. These results shed new insights in the innovation of design novel TiAl/RGO composites for SLM. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) method has a great potential for fabricating injection mold with complex structure. In this study, two S136 mold steel pre-alloy powders with trace element difference were fabricated by SLM, and then comparison of samples on microstructure, mechanical and corrosion resistant property was investigated. Results showed that the sample fabricated with a higher Si+Mn content exhibited the lower mechanical properties, such as micro-hardness of 48.73 HRC, ultimate tensile strength of 1186.7 MPa and elongation of 10.6% due to a few of pores observed on the cross surface. For the SLM sample produced by another powder with a lower Si+Mn content, it showed equiaxed grains and cellular dendrite grains coexisted and exhibited the superior mechanical properties (50.31 HRC, 1467.9 MPa and 11.1%) combined with well corrosion resistance. Then the injection mold insert with conformal cooling channel was successfully processed by this powder. The cooling time was reduced by 30% during the injection cycle. Therefore, it can be seen that trace element differences have an important effect on the SLM S136 mold steel. The results suggest that it is essential for successful fabricating components with a suitable composition of alloy during SLM process. [ABSTRACT FROM AUTHOR]

Polyamide 6 (PA6) have been extensively employed in manufacturing engineering plastic alternatives to metal in automotive field owing to their high specific strength, good damping and thermal properties. However, the selective laser sintering (SLS) availability of high performance PA6 is not thoroughly investigated. This paper firstly investigates the processability, recyclability and crystalline structure of SLS PA6 powder in comparison with the widely used Polyamide 12 (PA12). The results show that the PA6 powder has a relatively sphere shape, an appropriate average particle size 58.9 μm, a wide sintering window up to 36.73 °C (c. 6 °C wider than PA12) and similar crystallinity 47.61% comparable to PA12, indicating an excellent SLS processability. However, the used PA6 powder shows a directly fragmenting behavior, a substantially narrowed sintering window (decreased by 13.15 °C) and a dramatically declined crystallinity (down to 21.8%), indicating a relatively inferior recyclability compared with PA12. The sub-T pm1 crystallization transition concerning α phase was found for SLS PA6 part, which is derived from the release of strain energy absorbed during SLS processing and has advantageous effects on part ductility. This work confirms that it is available and promising for the application of high performance PA6 in SLS. [ABSTRACT FROM AUTHOR]

Considering the effects of numbers and drill processes of film cooling holes, the effect of a multiaxial stress state on the creep behavior of Ni-based single-crystal superalloy was investigated. The thin-wall plate specimens with film cooling holes, including multiholes and a single central hole, have been designed. The drilling processes are electro stream machining (ESM), electrical discharge machining (EDM) and laser drilling (LD). The results show that creep lives were longer in the thin-wall specimens with a single central hole and shorter in specimens with multi-holes due to the multihole interference effect. Under the same stress and temperature, the specimens with multiholes using the LD process have the longest creep lives compared with the other two processes. To predict the creep life of a specimen with film cooling holes, a creep damage constitutive model under the crystal plasticity framework was proposed by adding geometric structure variables β and m . Coupling with the modified skeletal point stress method (SPSM), the creep rupture lives of the specimens with film cooling holes were well predicted. The error of creep life between the finite element (FE) calculation and experimental results is within 28.03%. [ABSTRACT FROM AUTHOR]

Laser sintering (LS) has capability of manufacturing complex structures and functional parts. However, material aging and part performance stability are still challenges to face in LS irrespective of protective atmosphere. Consequently, this work focuses on the essence of these problems and investigations on systematical mechanism of PA-12 aging and its micro-structural evolution during LS. The results show that the mechanism mainly has two opposite aspects concerning the material processability. On one hand, analogous Brill transition of peak merging, which is discovered for the first time in the powder aging process of LS PA-12 material, leads to a higher oneset melting temperature of the aged powder and broadens the sintering window more than 1 °C after 3 recycling. On the other, the existence of solid-state and melt-state polycondensation, which is proved by XPS and rheological measurements, induces the higher temperature nucleation for the aged powder and the crystallization postponement for aged LS parts detected in DSC. The effect of solid-state polycondensation reduces the crystallinity of the powder by ∼6% after 3 recycling. This mechanism is of the guiding significance for powder stability improvement and consistent control of component properties next. [ABSTRACT FROM AUTHOR]

The surface slip deformation characteristics around two different patterns of film cooling holes in perforated plates were investigated by room-temperature tensile testing. An ARAMIS system was employed to observe the strain distribution on the sample surface. The development of slip traces and the microstructure after fracture of the specimens were analyzed by optical microscope (OM) and scanning electron microscopy (SEM), respectively. The maximum surface strain of the specimens with a triangular penetration pattern measured by the ARAMIS system was found to be larger than that of the perforated square-patterned specimens at both the yield point and when approaching fracture. However, specimens with a triangular penetration pattern have a greater yield strength and ultimate tensile strength than the specimens with a square penetration pattern because the cross-cleavage fracture of the specimen with the square penetration pattern leads to larger damage than the single-slip deformation fracture of the specimen with the triangular penetration pattern. Octahedral slip systems of the two kinds of specimens were activated in the same slip system, and the slip band observed in the experiment is consistent with crystal plasticity theory. [ABSTRACT FROM AUTHOR]

One of the first attempts on fabricating functionally graded materials (FGMs) of titanium/hydroxyapatite (Ti/HA) with quasi-continuous ratios by selective laser melting (SLM) was done. HA ratios varied among the layers of FGMs from 0 wt% to 5 wt% with 1 wt% gradient. The 3D reconstruction of Ti/HA FGM bulk with micro-pores was presented through micro-CT, and the percentage of micro-pore increased from 0.01% to 3.18% with the increasing of HA ratio. The scanning electronic microscope results showed that the crack was positively correlated to HA ratio with the crack density increasing from 1.5 × 10 − 4 μm/μm 2 to 2.7 × 10 − 3 μm/μm 2 . The microstructure evolution from 0% to 5% HA ratios could be elucidated as long lath-shaped grains → long acicular-shaped grains → short acicular-shaped grains → continuous circle-shaped grains → quasi-continuous circle-shaped grains, due to the perturbation in the melting pool and obstruction of crystal development by HA. Accordingly, the FGM provides a wide range of nanohardness from 5.11 to 8.36 GPa and Vickers hardness from 3.42 to 5.67 GPa. Moreover, the fracture toughness from 2% to 5% HA ratios ranges from 3.41 MPa m 1/2 to 0.88 MPa m 1/2 , which can be tailored to fit that of cortical and cancellous bones. [ABSTRACT FROM AUTHOR]