Mechanical Properties and Corrosion Resistance of NbTiAlSiZrNx High-Entropy Films Prepared by RF Magnetron Sputtering.

In this study, we designed and fabricated NbTiAlSiZrNx high-entropy alloy (HEA) films. The parameters of the radio frequency (RF) pulse magnetron sputtering process were fixed to maintain the N2 flux ratio at 0%, 10%, 20%, 30%, 40%, and 50%. Subsequently, NbTiAlSiZrNx HEA films were deposited on the 304 stainless steel (SS) substrate. With an increasing N2 flow rate, the film deposited at a RN of 50% had the highest hardness (12.4 GPa), the highest modulus (169 GPa), a small roughness, and a beautiful color. The thicknesses of the films were gradually reduced from 298.8 nm to 200 nm, and all the thin films were of amorphous structure. The electrochemical corrosion resistance of the film in a 0.5 mol/L H2SO4 solution at room temperature was studied and the characteristics changed. The HEA films prepared at N2 flow rates of 10% and 30% were more prone to corrosion than 304 SS, but the corrosion rate was lower than that of 304 SS. NbTiAlSiZrNx HEA films prepared at N2 flow rates of 20%, 40%, and 50% were more corrosion-resistant than 304 SS. In addition, the passivation stability of the NbTiAlSiZrNx HEA was worse than that of 304 SS. Altogether, these results show that pitting corrosion occurred on NbTiAlSiZrNx HEA films.

Microstructure Evolution and Deformation Behavior of Extruded Mg-5Al-0.6Sc Alloy during Room and Elevated Temperature Tension Revealed by Ex-Situ EBSD and VPSC.

In this study, the microstructure evolution and deformation behavior of the extruded Mg-5Al-0.6Sc (AS51) alloy during tensile testing at room temperature (RT) and 250 °C were investigated by electron backscattered diffraction (EBSD) characterization and Visco Plastic Self Consistent (VPSC) simulation. The results showed that a continuous hardening behavior of the alloy occurred during the deformation at RT, and a certain softening was caused by the occurrence of dynamic recovery (DRV) and dynamic recrystallization (DRX) in the late stage of deformation at 250 °C. The primary deformation mechanism at both RT and 250 °C was dislocation slip, with prismatic slip being the dominant deformation mode, and no significant changes in grain size or texture type occurred. By identifying the activated twin variants, the results indicated that the selection of twin variants was closely related to the local stress concentration. The relatively low activation frequency of extension twinning at 250 °C is partly attributed to the fact that the consumption of dislocations by DRV and DRX can effectively relax the local stress concentration. Meanwhile, the DRX mechanism during the deformation of the alloy at 250 °C was mainly discontinuous dynamic recrystallization (DDRX), with a low recrystallization fraction.

[Spectroscopic characterization and properties of Mg2B2O5w/AZ91D magnesium composites].

Magnesium borate whisker (Mg2B2O5 w) reinforced Mg matrix composite was fabricated by vacuum-gas pressure infiltration process. The Mg2B2O5 w preforms forming process was determined. The Mg2B2O5 whiskers were fabricated into a preform by wet forming method without any binder. The Vacuum-Gas Pressure Infiltration process and parameters are also developed. The micrographs revealed reasonably uniform distribution and random orientation of the whiskers in the as-cast Mg2B2O5 w/AZ91D composite and the composites were without pores defect. The phases were analyzed by XRD patterns for the as-received whiskers, the whiskers sintered at 1 000 degrees C for 3 h and the as-cast composite, respectively. Then, the microstructure evolution of the composite was investigated when the composite was heat-treated. Meanwhile, the relationships between microstructure and micro-hardness of the alloy heat-treated were also studied. The heat-treatment condition were solution at 415 degrees C for 8 and 24 h, respectively, aging treatment at 200 degrees C for 8, 12, 16, 20 and 24 h, respectively and solution at 415 degrees C for 8 or 24 h and subsequent aging treated for 8, 12, 16, 20, 24 h, respectively. The phases were analyzed by XRD patterns for the composites after different heat treated process. The results of XRD patterns were shown to be in good agreement with the microstructures evolution of the composites. The results showed that the micro-hardness of the solution treated composites is decreased due to resolution of eutectic phase, whereas the micro-hardness of the aged composites was increased gradually and the peak hardness is reached to 201 HV in the composite aged for 16 hours. Solution treatment at 415 degrees C for 24 h, the beta-Mg17, Al12 phase is dissolved in the alpha-Mg phase to form oversaturated solid-solution in the composite and then the diffusive beta phase precipitates after subsequent aging treatment at 200 degrees C for 8 h; hence the micro-hardness of the composite was increased 30%. However, as the aging time increased to 24 h, the hardness of the composite was reduced to 183 HV because the beta-Mg17 Al12 phase precipitate changed from continuous fine platelets to discontinuous coarse platelets. It was concluded that the process of solution at 415 degrees C for 24 h and subsequent aging treatment at 200 degrees C for 8 h was the best process for the composite.