Search

Effects of electropulsing treatment (EPT) on the microstructure evolution, mechanical properties and crack healing of intermetallic Al 3 Ti alloys were studied in this work. In order to investigate the athermal effect caused by EPT, conventional heat treatment (CHT) was conducted for comparison. The compressive stress-strain curves demonstrated that the failure strains of Al 3 Ti alloy increase under both the EPT and CHT conditions, while the increment of failure strain of Al 3 Ti alloy treated by EPT is higher than that treated by CHT. Fracture surface analysis confirmed that the intrinsic brittle fracture of Al 3 Ti alloy evolves into the quasi-cleavage fracture with increasing frequency of EPT. Based on the systematic investigation into the microstructure evolution, mechanical properties and fracture surface observation, the influence mechanism of EPT on Al 3 Ti alloy was found to be related to the improvements of atomic diffusion and dislocation movement, which results from the coupling of thermal effect and athermal effect by EPT. Furthermore, the thermal compressive stress and athermal effect could heal the local micro-crack and decrease the crack width of Al 3 Ti alloy by EPT. Therefore, EPT can work as a novel method for improving the plastic deformation capacity of Al 3 Ti alloy. [ABSTRACT FROM AUTHOR]

A novel specimen was designed to study the interface tensile behavior and fracture mechanism of the Ti/Al 3 Ti Metal-Intermetallic Laminate (MIL) composite under quasi-static and high strain rates. The experimental results indicated that the interface tensile strength of the Ti/Al 3 Ti MIL composite increases with increasing strain rate. The fracture mechanisms of the Ti/Al 3 Ti MIL composite are different under quasi-static (~0.001/s) and high strain (~300/s) rates. Generally, fracture only occurs in the interface under quasi-static tensile condition, while the fracture is also found in Al 3 Ti layer apart from the interface under high strain rate. The quasi-cleavage features are visible in the interface surface of Ti layer in both quasi-static and high strain rates. Moreover, large dimples are found in the fracture surface under high strain rate, and the tearing ridges are more than that under quasi-static strain rate. The brittle Al 3 Ti layers show an intergranular fracture behavior, along with minor transgranular fractures and secondary micro-crack formed in the grain boundary. [ABSTRACT FROM AUTHOR]

A novel Shape Memory Alloy NiTi fiber-reinforced metal-intermetallic–laminate (SMAFR-MIL) composite with a volume fraction of ~ 3.5% NiTi was fabricated using vacuum hot pressing method in this paper. The microstructure characterization of this laminate composite was performed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD), and the mechanical property of SMAFR-MIL composite was determined by compression test. In addition, damping capacity was measured using Dynamic Mechanical Analyzer (DMA) in a temperature range from 30 °C to 50 °C. The experimental results indicated that the average compressive strength and the strain to failure are ~ 1208 MPa and ~ 4.4% for loading perpendicular to the layers, and ~ 962 MPa and ~ 4.8% for loading parallel to the layers, respectively. The loss modulus of SMAFR-MIL composite is ~ 3.7 GPa, which is five times greater than that of Ti/Al 3 Ti laminate composite without NiTi fiber reinforcement, while the damping factor of SMAFR-MIL composite is ~ 4.5%. Both the mechanical and damping tests demonstrated that SMAFR-MIL composite is a new class of structural and functional composite with superior mechanical and damping properties. [ABSTRACT FROM AUTHOR]

Abstract: The compressive mechanical properties of Mg–8Li–1Al–1Ce alloy were investigated under quasi-static strain rates (0.0001/s, 0.001/s, 0.01/s, and 0.1/s) and high strain rates up to ∼2700/s at room temperature. The experimental results indicate that the flow stress and strain rate sensitivity increase with increasing strain rate. Microstructure observation by optical microscopy reveals that the distribution of compound Al2Ce is influenced by the strain rate: when strain rate is higher, the compounds Al2Ce distribute in both α and β phases; when strain rate is lower, most of the compounds Al2Ce distribute in β phase and in the boundaries between α and β phases. Furthermore, it is found that the twinning forms in extruded Mg–8Li–1Al-1Ce alloys when deformed at high strain rates, and the amount of twinning increases with increasing strain rate, the deformation mechanism of Mg–8Li–1Al–1Ce alloy at high strain rates is a combination of dislocation motion and twinning. [Copyright &y& Elsevier]

The novel aluminum matrix (Al-matrix) syntactic foam with multi-shelled hollow sphere structure (HSS) was fabricated by introducing double-layered 316L-Al 2 O 3 metal-ceramic hollow spheres (M-C HSs) through powder metallurgy method. Microstructure characterization and mechanical properties of multi-shelled HSS have been investigated by XRD, SEM, TEM/EDS and nanoindentation. Quasi-static compressive tests of Al matrix, Al-matrix syntactic foams with Al 2 O 3 HS and M-C HS have been performed. Compressive strength (σ 0.2), plateau stress (σ p), plateau end strain (ε p e ), and energy absorption (W 50) were used to analyze the effect of multi-shelled HSS in the syntactic foam. The results showed that in multiple interfaces formed in the syntactic foam, main elements diffusion was found in interface between Al 2 O 3 and 316L shells. While, the intermetallic shell formed in interface between 316L shell and Al matrix was composed of Fe 4 Al 13 substrate, and precipitations of Cr phases and Mo-rich phases. Therefore, a "ceramic-metal-intermetallic" multi-shelled HSS was formed in syntactic foam with M-C HS. Compressive strength of the syntactic foam was increased by 8.04% compared with that of syntactic foam with Al 2 O 3 HS, which led to high energy absorption (W 50 = 93.28 MJ/m3). Deformation mechanism of multi-shelled HSS has been discussed in this work. [ABSTRACT FROM AUTHOR]

• A series of Fe-based amorphous coatings were fabricated via laser cladding assisted with ultrasonic vibration. • With increasing ultrasonic power from 0 W to 1000 W, the average thickness of the gradient crystallization zone increases from 46 μm to 81 μm and appears as a changed wave. • The gradient structure has an energy storage function that can release internal stress and reduce coating cracking. Fe-based amorphous coatings were deposited on 20# mild steel using laser cladding assisted with ultrasonic vibration under different ultrasonic powers from 0 W to 1000 W. When the ultrasound is introduced into the molten pool, it can increase the maximum temperature and life cycle and promote the solute exchange at the bottom of the molten pool. While it has little effect on the molten pool top's temperature field and element distribution. With increasing ultrasonic power, the gradient crystallization structure between the substrate and the amorphous coating increases from 46 μm to 81 μm and appears as a changed wave. The cracking trend of the coating decreases with increasing crystallization zone, which is similar to a spring, with an energy storage function that can release internal stress and reduce coating cracking. Interestingly, the amorphous phase still dominates the top zone of the Fe-based amorphous coating without influencing its function. [ABSTRACT FROM AUTHOR]

[Display omitted] • Induced the acoustic streaming to accelerate gas bubbles to escape the molten pool. • Drag force causes the significant differences in the motion trajectories of bubbles under acoustic streaming. • Using acoustic streaming to concentrate non-escape bubbles at the molten pool edge. • The hybrid processing methods has enhanced the porosity reduction effect by ultrasonic effect. Pore defect plays an important factor on leading to a decrease in the strength performance and reliability of deposition layers manufactured by directed energy deposition (DED). The ultrasonic energy field assistant method usually improves the structure of materials, now is induced to reduce porosity by acoustic streaming driven effect in directed energy deposition process. In this work, 1Cr12Ni3MoVN powder (29% hollow particles) was used to controllable generate bubbles in the molten pool to induce the imperfect deposition conditions in the experiments. The distribution of pores with different laser processing parameters under ultrasonic vibration (UV) was investigated, and the principle that ultrasonic vibration drives the bubble motion under the complex physical environment was also analyzed by numerical simulation. The results show that acoustic streaming lead by UV effect, in competition with other flows (Marangoni flow and non-isothermal flow), makes the small bubbles to escape or large bubbles to move toward the edge of the molten pool. In general, UV reduces porosity from an average of 0.61% to 0.31%. Combined with the subtractive method, the porosity reduction rate has been improved from 45% to 82%. UV finally resulted in an average increase of 17% in the elongation of the material. This work provides the understanding on the driving effect of acoustic streaming on bubble motion and guide a novel way to reduce the porosity of DED technology. [ABSTRACT FROM AUTHOR]

• Building three optimized machine learning methods to predict melt pool shape. • Utilization of melt pool shapes derived from a large number of directed energy deposition experiments as data sets. • Prediction accuracy varies between models applying different algorithms, with accuracy of up to 96% or more. Directed Energy Deposition (DED), one type of additive manufacturing (AM) as novel modern manufacturing technology, is widely employed to fabricate materials layer by layer through digital models. It is well known that the shape of the melt pool is influenced by the manufacturing process parameters during the manufacturing process, which can affect the performance of the part. Therefore, three machine learning models, support vector regression (SVR), extreme gradient boosting (XGBoost), and back propagation neural network (BPNN), were selected and constructed in this study to predict melt pool shape and to maximize prediction performance by integrating various algorithms and parameters. Meanwhile, the geometry of the melt pool, such as the height, width, and depth of 210 single-channel deposition layers, were measured as training and testing datasets, which can be supplied the basic data for training the prediction models and testing the prediction performance of models. In addition to the training and test datasets, a new dataset with 36 samples was created to validate the performance predictions made by the three machine learning models. The results demonstrate that, based on the test dataset, the RBF kernel-based SVR model predicts the melt pool height with an accuracy of ∼ 93 %, while the XGboost model predicts the melt pool width and depth with accuracy rates of ∼ 97 % and ∼ 96.3 %, respectively. In the new dataset, the BPNN model based on Adam's method achieves a prediction accuracy of ∼ 93.7 % for melt pool height, but the XGboost model achieves ∼ 96.6 % and ∼ 97.8 % for melt pool width and depth, correspondingly. Thus, in addition to the training and testing datasets, the enhanced machine learning models exhibited remarkable prediction accuracy, excellent generalization, and robustness in the new dataset. As a result, the application of machine learning has greatly improved the possibility of controlling the DED process more intelligently and stably. [ABSTRACT FROM AUTHOR]

The present work investigated the evolution of (Ti, Mo)C particles in austenite of a Ti-Mo-bearing steel during isothermal holding after hot deformation at 925 °C. Results show that the (Ti, Mo)C particles sequentially undergo dislocation-assisted diffusion controlled growth stage, interface-reaction controlled slow coarsening stage, and bulk diffusion controlled fast coarsening stage. The Mo-enriched region near the outer layer of the (Ti, Mo)C particles results in the slow coarsening stage. To reduce the total interface and strain energy correlated with austenite matrix, the particle morphology evolution follows spherical → polyhedral → irregular route. Compared to TiC, dispersive refined (Ti, Mo)C particles suppress austenite recovery and recrystallization more effectively, which favors maintaining the deformed microstructures at high temperatures. [ABSTRACT FROM AUTHOR]

The tensile and compressive behaviors of an extruded Mg- 8 Y- 1 Er-2Zn alloy containing a long period stacking ordered (LPSO) phase were investigated. Compared with the tensile results, the alloy exhibits higher values of the yield stress, strain to failure and work hardening rate in compressive tests, which indicates that the alloy exhibits an asymmetry of tensile-compressive mechanical behaviors. The LPSO phase cracks during tensile deformation while it exhibits a kinking characteristic in the process of compression. It can be concluded that the two different deforming modes of the LPSO phase are the cause of the asymmetry of tensile-compressive mechanical behaviors. [ABSTRACT FROM AUTHOR]

• An automated impact fatigue system was newly developed. • The impact fatigue behavior of LMD 316L stainless steel were investigated. • The fatigue life decreased with the increasing loading rate. • The mechanism of loading rate on fatigue life was revealed. Repeated impact subjecting on the key components of equipment is always characterized by extremely high loading rate loading, while plastic deformation of most metals depends on loading rate. To ensure the reliability and security of these components, it is necessary to understand the loading rate effect on the fatigue performance. In this study, an automated impact fatigue system based on split Hopkinson bar technique was newly developed to investigate the materials' impact fatigue behavior. Impact fatigue behavior and non-impact fatigue behavior of laser metal deposition 316L stainless steel were analyzed. The fatigue life decreases with the increasing loading rate, implying the significant loading rate dependence. The compression and fracture toughness tests combined with fractography analysis at high and low loading rates were also conducted to reveal the underlying mechanism of the difference between impact and non-impact fatigue life. Finally, microstructure of the laser metal deposition 316L stainless steel after impact and non-impact fatigue was characterized. It can be concluded that the fatigue crack is apt to initiate under impact fatigue due to the high density of dislocation entanglement, while under non-impact fatigue, a large number of twins are beneficial to delay the fatigue crack initiation. [ABSTRACT FROM AUTHOR]

• A hybrid fabrication method combining additive manufacturing (AM) and ultrasonic impact treatment (UIT) techniques was further investigated. • The strain rate controlling factors and stress-strain relationship of the additive manufactured sample in SHPB tests were theoretically analyzed. • A finite element model was established to analyze the impact-rebound-impact process of UIT. • The stress and plastic strain fields were analyzed numerically and experimentally. A hybrid fabrication method combining additive manufacturing (AM) and ultrasonic impact treatment (UIT) techniques was developed to improve the microstructure and mechanical properties of additive manufactured metal parts. Experimental and numerical methods were conducted to analyze the stress and strain fields of ultrasonic impact on additive manufactured parts. Laser metal deposition (LMD) technique was applied to prepare the 304 stainless steel (SS) samples and then the samples were post-treated by UIT. Considering high strain rate effect of metallic materials in the UIT process, the dynamic hardening properties of the as-deposited 304 SS sample were experimentally measured using a split Hopkinson pressure bar (SHPB) technique. The strain rate controlling factors and stress-strain relationship of the as-deposited sample in the SHPB tests were theoretically analyzed. The dynamic and high transient impact-rebound-impact process of UIT including the pin velocity, stress field and plastic strain field were investigated numerically via a three-dimensional finite element model. The impact stress field parameters such as the magnitudes and directions of principal stress and principal shear stress were investigated to further analyze the plastic deformation behavior of the deposited sample. The experimental results of plastic deformation zone obtained from optical microscopy, electron backscatter diffraction (EBSD) and microhardness testing are in good agreement with the numerical results. Both the experimental and numerical results confirm that UIT can effectively improve the performance of additive manufactured metal parts. [Display omitted] [ABSTRACT FROM AUTHOR]

• At a strain rate 3800 s−1, the dual-phase steel shows a high flow strength of 4067 MPa. • The framework structure weakens the local strain within the sample. • High-strain-rate deformation promotes the structure transformation of nanoprecipitates, alleviating strain concentration. High–strain–rate deformation of steels is prone to generating localized adiabatic shear bands (ASB) due to strain localization, leading to plastic instability and fracture. Nanoprecipitate–strengthened austenite–martensite dual–phase (DP) steel is a kind of promising impact–resistant materials due to their high strength and excellent plasticity. In this study, the effects of a combination of nanoprecipitates and the frame structure of DP steels with the hard martensite as the support framework on the dynamic mechanical properties were systematically investigated. The nanoprecipitate–strengthened DP steel exhibited excellent dynamic performance. At a strain rate of 3800 s−1, the maximum flow stress of the DP steel with nanoprecipitates reached ∼ 4067 MPa, which was 1146 MPa higher than its counterpart without nanoprecipitates. High–strain–rate deformation induced the transformation of Cu–rich nanoprecipitates from body–centered cubic (B2) to 9R twin structure, alleviating the stress concentration. Upon high–strain–rate deformation, the high strength of nanoprecipitate–strengthened DP steel induced the formation of a narrow shear band with sever–deformed microstructure. The frame–structure of DP steel restrained the transformation of deformed shear bands (DSB) to transformed shear bands (TSB) due to the deformation–induced martensitic transformation of austenite, delaying the crack formation and propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

To improve the ductility of Al 3 Ti alloy, the continuous shape memory alloy NiTi fiber (CSMAR) was introduced into intermetallic Al 3 Ti matrix for fabricating the novel CSMAR-Al 3 Ti composite in this work. Microstructure characterizations demonstrated that the CSMAR-Al 3 Ti composite mainly consists of Al 3 Ti layer, NiTi fiber, eutectic area and interfacial reaction layer. EBSD results indicated that the eutectic area is made up of Al 3 Ti and Al 3 Ni phases, the Al 3 Ti phase shows a strong [001] crystallographic oriented structure, while the Al 3 Ni phase has a non-textured structure. TEM results showed that the interfacial reaction layer between NiTi fiber and eutectic area is a multiple phase mixture, including various Ti-Al and Ni-Al intermetallics. Furthermore, TEM and HRTEM analyses revealed a newly formed Ti 2 Ni layer between NiTi fiber and interfacial reaction layer. Tensile test results confirmed that the CSMAR-Al 3 Ti composite could effectively improve the ductility of the Al 3 Ti alloy. Based on the systematic investigations of interfacial microstructure characterization, mechanical behavior and fracture morphology observation, it is found that the toughening mechanism of CSMAR-Al 3 Ti composite is related to the interfacial fine grain strengthening effect with the gradual distribution characteristic. In addition, the excellent metallurgical bonding between fiber reinforcement and matrix is also beneficial to the mechanical properties. [ABSTRACT FROM AUTHOR]

Intermetallic Al 3 Ti alloys with different volume fractions of residual aluminum were synthesized via reactive foil sintering in vacuum condition using commercial purity aluminum foils and Ti-6Al-4V alloy foils. Microstructure evolution, elemental analysis, fracture mechanism and phase identification were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) technique, respectively. Mechanical properties were measured by quasi-static compression and Vickers hardness tests. Experimental results indicated that the ductile phase Al distributes in the grain boundaries of the brittle matrix Al 3 Ti, which increases the compression failure strain of the Al 3 Ti alloy dramatically compared with the monolithic intermetallic Al 3 Ti alloy. The compressive stress-strain curve showed a typical elastic-plastic deformation behavior. Moreover, it also demonstrated that the post-heat treatment plays an important role in the mechanical properties due to the formation of α-Al 2 O 3 and Al 3 Ti grain coarsening. [ABSTRACT FROM AUTHOR]

Metallic hollow spheres and polyurethane resin are excellent sound insulation and sound absorption materials. In this study, the surface modified 316L stainless steel hollow spheres were added into polyurethane by casting method. The influence of the volume fraction and diameter of the hollow spheres on the sound insulation and sound absorption performance of the Metallic-Hollow-Sphere/Polyurethane (MHSP) acoustic composites was investigated by impedance tube method and the relevant acoustic mechanism was discussed. When the volume fraction of hollow spheres is 45% and the diameter is 2.5 mm, composite has the best sound insulation performance. And when the volume fraction of hollow spheres is 60% and the diameter is 2.5 mm, composite has the best sound absorption performance. Due to the mass effect, damping effect, change of acoustic impedance and multiple interface of composites, sound waves will reflect, refract and scatter many times in the process of propagation, thus losing lots of sound energy to improve the sound insulation performance. The sound absorption mechanism of MHSP is that the friction, viscosity and reflection of sound waves in the pores of polyurethane, cavities of the hollow spheres and interfaces will cause the loss of sound energy and turn it into heat energy. [ABSTRACT FROM AUTHOR]

In this paper, a Ti6Al4V-Mg3AlZn laminate metal composite (TC4-AZ31 LMC) was successfully prepared by hot pressing sintering. The interfacial microstructure of this composite was investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and high resolution transmission electron microscopy (HR-TEM). The three-point bending (TPB) tests of TC4-AZ31 LMC were performed to determine the foil-foil interface bonding properties. Results show that the AZ31 matrix of the TC4-AZ31 LMC possesses a strong {10-10} <0001> sheet texture and the adjacent AZ31 foils are bonded well through the migration of grain boundaries across the original boundaries of the foils. A continuous interfacial reaction layer consisting of an intermetallics layer, a nanocrystalline-amorphous mixture layer and a bulk-precipitated particles region was formed around the TC4/AZ31 interface. The intermetallics layer bordering on TC4 reinforcement was identified as Al 192.40 Fe 46.22 phase. The nanocrystalline-amorphous mixture layer was composed of MgO nanocrystalline and Mg-O amorphous phase. The bulk-precipitated particles locating at the boundary of AZ31 matrix were determined as complex precipitates containing Al 6 Mn and Al 13 Fe 4 phases. Compared with the AZ31 alloy, the TC4-AZ31 LMC possessed a superior bending strength, which is attributed to the effective load transfer capability from the AZ31 matrix to high strength TC4 reinforcement through the well-bonded TC4/AZ31 interface. • The interfaces of TC4-AZ31 LMC were studied by EBSD and TEM systematically. • The extremely thin intermetallics and nanocrystalline-amorphous reaction layers were formed along the TC4/AZ31 interface. • The grains of AZ31/AZ31 interface were bonded together by grain boundaries migration. • The composite showed superior bending properties than AZ31 alloy. [ABSTRACT FROM AUTHOR]

In this study, the polyurethane/316L stainless steel hollow spheres (PU/316L HS) and silicone rubber/316L stainless steel hollow spheres (SR/316L HS) composites were prepared by casting method. The sound transmission loss of polyurethane composites and silicone rubber composites increased after adding metallic hollow spheres. The sound insulation performance of hollow sphere composite is closely related to the acoustic reflection and diffraction at the interface. In addition, silicone rubber with better molecular flexibility is easier to reflect sound waves than polyurethane, thus reducing the passing sound energy, so it has greater sound transmission loss. For the sound absorption performance of materials, the PU has a maximum absorption coefficient of 0.87 at 3550 Hz, but the absorption coefficient of the PU/316L HS composite moved to the lower frequency. The reason for this phenomenon is that the hollow spheres change the elastic modulus of polyurethane, which causes the resonance frequency of material and air to move to lower frequency, so the range of sound absorption frequency changes. Moreover, the different proportion of free volume in polyurethane and silicone rubber matrix is the main reason for the great difference of their sound absorption properties. [ABSTRACT FROM AUTHOR]