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Compared with conventional casting process, laser direct metal deposition (LDMD) can effectively reduce component segregation in non-equiatomic high entropy alloys (HEAs). However, the non-equilibrium thermal history imparted by this method has a significant effect on the microstructure and mechanical properties of the HEA. The present work prepared non-equiatomic (FeNiCo)-(AlCrSiTi) HEAs using the LDMD process, after which some samples were subjected to a subsequent vacuum remelting (VRM) treatment. The variations in phase composition, microstructure and hardness between the HEAs processed using the LDMD or VRM methods were investigated. Differences in phase composition increased with increases in the proportion of the Al, Cr, Si and Ti components. Compared with the HEA samples processed using the VRM method, the LDMD specimens possessed much finer and simpler microstructures mainly comprising solid solution phases. At relatively high concentrations of the Al, Cr, Si and Ti components (32 at% and 40 at% in total), the HEAs processed under LDMD conditions had similar grain morphologies, intermetallic phases and microhardness values, while the VRM specimens presented completely different microstructures and properties.

Owing to the easy-to-crack in the weld zones (WZ) of titanium alloy/steel bimetallic sheets, sequentially layered-to-layered welding, by using various filler metals, is widely adopted to join the bimetallic sheets. In this study, multi-principal filler powders of FeCoCrNiMn, as only one type of filler metal, were used to join TA1/Q345 bimetallic sheets by laser deposition welding. Microstructure evolution, microhardness, and tensile properties in the joint of TA1/Q345 bimetallic sheets were studied. The results indicated that TA1/Q345 bimetallic sheets could be joined by using multi-principal filler metal when the groove root was opened in the Q345 base plate. Significant transition zones were found at the TA1/WZ and Q345/WZ interfaces. The structures of α-Fe, β-Ti, β-Ti + TiFe, and α-Fe + TiFe2 were formed in the transition zones. The solidified primary phases of TiFe2 and the eutectic structures of α-Fe + TiFe2 were observed in most regions of the WZ. Various intermetallic compounds (IMCs) of TiFe and TiFe2, as well as the snowflake-like structures of TiC, coexisted in the WZ near the flyer and base layers, which were significantly harmful to the formability of the WZ and caused a crack in the WZ. The markedly high hardness and low tensile strength were presented in the WZ. A sawtooth-like fracture line was observed. The fracture line was extended from the WZ/base metal (BM) interface to the WZ center, in which the minimum hardness (∼523 HV0.2) and many eutectic structures were presented.

Owing to the high strength and plasticity, high-entropy alloys (HEAs) can be used as filler metals to achieve high-quality joints. However, the melting base metal in fusion welding can significantly change the chemical composition of the weld zone (WZ), which may cause the failure of high-entropy effects in the WZ. In the present study, a high-entropy filler metal of CoCrNiMnAl0.6Ti0.3Si0.1 was used to join the dissimilar metals of SMA490BW steel and 304 stainless steel. Two types of joints were obtained by whether the welding plates had a V-groove or not. The effects of workpiece groove on the microstructure, element distribution, phase structure, microhardness, and tensile strength of dissimilar joints, as well as the controllability of the high-entropy effects in WZ were explored. It was found that a 60° V-groove in the workpiece could significantly reduce the amount of Fe element in the WZ. Microstructures in the WZs were changed from columnar/equiaxed grains of the No V-groove sample to lamellar structures of the V-groove sample. The microhardness in the WZ of the latter was 33% higher than that of the former. The reason was mainly related to the phase structures in two WZs. Two types of samples had a similar notched tensile strength, which was higher than SMA490BW steel, and lower than 304 stainless steel.

Abstract Freeze-drying can be used to ensure off-the-shelf availability of decellularized heart valves for cardiovascular surgery. In this study, decellularized porcine aortic heart valves were analyzed by nitroblue tetrazolium (NBT) staining and Fourier transform infrared spectroscopy (FTIR) to identify oxidative damage during freeze-drying and subsequent storage as well as after treatment with H2O2 and FeCl3. NBT staining revealed that sucrose at a concentration of at least 40% (w/v) is needed to prevent oxidative damage during freeze-drying. Dried specimens that were stored at 4 °C depict little to no oxidative damage during storage for up to 2 months. FTIR analysis shows that fresh control, freeze-dried and stored heart valve specimens cannot be distinguished from one another, whereas H2O2- and FeCl3-treated samples could be distinguished in some tissue section. A feed forward artificial neural network model could accurately classify H2O2 and FeCl3 treated samples. However, fresh control, freeze-dried and stored samples could not be distinguished from one another, which implies that these groups are very similar in terms of their biomolecular fingerprints. Taken together, we conclude that sucrose can minimize oxidative damage caused by freeze-drying, and that subsequent dried storage has little effects on the overall biochemical composition of heart valve scaffolds.

Owing to the cocktail effect in high-entropy alloys, a good combination of strength and toughness of a welded joint could be theoretically achieved, by modifying the elemental composition of the filler metals with a high-entropy design. However, few studies have concentrated on this issue so far. In the present study, multi-component mixed powders of (CrMnFe)x(CoNi)y, with five types of the content ratios of the body-centered cube (BCC) and face-centered cube (FCC) forming elements, were used as filler metals to achieve dissimilar welding between 304 stainless steel and Q235 carbon steel by laser deposition welding. By comparative analysis of the microstructures and mechanical properties of the dissimilar joints, the effects of an elemental composition factor of μ (μ = x/y) on the hardness, tensile and bending properties of the dissimilar joints were explored. It was found that the elemental composition of mixed powders had an impact on the mechanical properties of dissimilar joints. Too high or too low content of BCC/FCC forming elements in filler metals cannot promote the appropriate mechanical properties. As an increase in the content of BCC forming elements, the hardness in weld zones was significantly increased, especially for the mixed powders with a high value of μ (≥7/3). The powders of (CrMnFe)5(CoNi)5 resulted in the best comprehensive mechanical properties of the dissimilar joint.

Friction stir welding (FSW) is a solid-state joining technique, which can avoid surface distortion and grain coarsening, and is very suitable for the joining of magnesium (Mg) alloys. However, a pronounced and inhomogeneous deformation texture was usually formed in the stir zone (SZ) of Mg welds. This has significant effect on the joint strength and fracture behavior of FSW Mg joints. In this review, microstructure and texture evolutions in weld zone (WZ) are analyzed based on the electron backscatter diffraction (EBSD) data. Schmid factor (SF) changes for slip and extension twinning were observed and discussed. The localized plastic deformation and fracture mechanisms of Mg welds are analyzed. In addition, some methods for improving the joint strength of FSW Mg welds are tested. Finally, the research direction of FSW Mg alloys in the future is determined.

In this study, the effect of the hot-cold rolling process on the evolution of the microstructure, texture and magnetic properties of strip-cast non-oriented electrical steel was investigated by introducing hot rolling with different reductions. The results indicate that hot rolling with an appropriate reduction, such as the 20% used in this study, increases the shear bands and {100} deformed microstructure in the cold roll sheet. As a result, in our study, enhanced η and Cube recrystallization texture and the improved magnetic induction were obtained. However, hot rolling with excessive reduction (36–52%) decreased the shear bands and increased the α-oriented deformation microstructure with low stored energy. It enhanced the α recrystallization texture and weakened the η texture, resulting in a decrease in the magnetic induction. In addition, hot rolling promoted the precipitation of supersaturated solid solution elements in the as-cast strip, thereby affecting the subsequent microstructure evolution and the optimization of its magnetic properties.

Friction stir welding (FSW) is a promising approach for the joining of magnesium alloys. Although many Mg alloys have been successfully joined by FSW, it is far from industrial applications due to the texture variation and low mechanical properties. This short review deals with the fundamental understanding of weak zones from the viewpoint of texture analysis in FSW Mg alloys, especially for butt welding. Firstly, a brief review of the microstructure and mechanical properties of FSW Mg alloys is presented. Secondly, microstructure and texture evolutions in weak zones are analyzed and discussed based on electron backscatter diffraction data and Schmid factors. Then, how to change the texture and strengthen the weak zones is also presented. Finally, the review concludes with some future challenges and research directions related to the texture in FSW Mg alloys. The purpose of the paper is to provide a basic understanding on the location of weak zones as well as the weak factors related to texture to improve the mechanical properties and promote the industrial applications of FSW Mg alloys.

As material for key parts applied in the aerospace field, the Cu-Be-Co-Ni alloy sustains cyclic plastic deformation in service, resulting in the low cycle fatigue (LCF) failure. The LCF behaviors are closely related to the precipitation states of the alloy, but the specific relevance is still unknown. To provide reasonable regulation of the LCF properties for various service conditions, the effect of precipitation states on the LCF behaviors of the alloy was investigated. It is found that the alloy composed fully of non-shearable γ′ precipitates has higher fatigue crack initiation resistance, resulting in a longer fatigue life under LCF process with low total strain amplitude. The alloy with fine shearable γ′I precipitates presents higher fatigue crack propagation resistance, leading to a longer fatigue life under LCF process with high total strain amplitude. The cyclic stress response behavior of the alloy depends on the competition between the kinematic hardening and isotropic softening. The fine shearable γ′I precipitates retard the decrease of effective stress during cyclic loading, causing cyclic hardening of the alloy. The present work would help to design reasonable precipitation states of the alloy for various cyclic loading conditions to guarantee its safety in service.

● NH3 dispersion from a multi-floor pig building was compared to a single-floor building.● NH3 dispersed much further from the multi-floor pig building.● Wind speed, direction and source concentration were important for NH3 dispersion.● NH3 tended to accumulate in the east and west yards of the multi-floor pig building.● Higher wind speed was the likely cause of more NH3 accumulation in the yards. Multi-floor buildings for raising pigs have recently attracted widespread attention as an emerging form of intensive livestock production especially in eastern China, due to the fact that they can feed a much larger number of animals per unit area of land and thus alleviate the shortage of land available for standard single-floor pig production facilities. However, this more intensive kind of pig building will pose new challenges to the local environment in terms of pollutant dispersion. To compare the dispersion air pollutants (ammonia as a representative) emitted from multi- versus single-floor pig buildings, ammonia dispersion distance and concentration gradients were investigated through three-dimensional simulations based on computational fluid dynamics. The validation of an isolated cubic model was made to ensure the simulation method was effective. The effects of wind direction, wind speed and emission source concentration at 1.5 m (approximate human inhalation height) during summer were investigated. The results showed that the ammonia dispersion distance of the multi-floor pig building was far greater than that of the single-floor building on a plane of Z = 1.5 m. When the wind direction was 67.5°, the wind speed was 2 m·s−1 and the emission source concentration was 20 ppmv, the dispersion distance of the multi-floor pig building could reach 1380 m. Meanwhile, the ammonia could accumulate in the yard to 7.68 ppmv. Therefore, future site selection, wind speed and source concentration need to be given serious consideration. Based on the simulation used in this study with source concentration is 20 ppmv, the multi-floor pig buildings should be located 1.4 km away from residential areas to avoid affecting residents. The results of this study should guidance for any future development of multi-floor pig buildings.