Additive manufacturing of Cu-AI-Mn shape memory alloy with enhanced superelasticity

The Cu-based shape memory alloy(SMA)with highly oriented columnar crystals is an ideal candidate for the commercial application,especially the ones obtained through rapid cooling via additive manufacturing method.In this work,Cu_(71)Al_(18)Mn_(11)(at%)shape memory alloy with strong<001>texture columnar grains was successfully prepared by selective laser melting(SLM).An L27(313)orthogonal array was designed to systematically investigate the effects of laser power,scanning speed,scanning spacing,layer thickness and their interactions on the forming quality of Cu_(71)Al_(18)Mn_(11)alloys.Cu_(71)Al_(18)Mn_(11)alloys with density of 7.3204 g·cm^(-3)and relative density of 99.18%were successfully prepared when the laser power,scanning speed,scanning distance and layer thickness were 240 W,1000 mm·s^(-1),0.11 mm and 25μm,the transformation onset temperature(Ms),martensite phase transformation termination temperature(Mf),austenite phase transformation onset temperature(AS)and austenite phase transformation termination temperature(Af)are-21.84,-26.04,-15.75 and-12.36℃,respectively.The compression strength and fracture strain along the building direction(BD)were significantly superior to the scanning direction(SD),while the superelasticity of compression along the SD reached 2.50%,which was better than that of2.32%along BD.The mechanical property and superelasticity anisotropy due to the formation of columnar grains and texture were discussed.This study shows that SLM is a proposed method for the preparation of Cu-Al-Mn SMAs with high superelasticity,which provides a new strategy for enhancing the shape memory alloy superelasticity.

Annealing atmosphere-dependent capacitive energy storage

Electrostatic capacitors based on dielectrics with high energy density and efficiency are desired for modern electrical systems owing to their intrinsic fast charging-discharging speed and excellent reliability.The longstanding bottleneck is their relatively small energy density.Herein,we report enhanced energy density and efficiency in the Aurivillius Pb_(2)Bi_(4)Ti_(5)O_(18)films by controlling the post-annealing atmosphere.The results demonstrate that the fabrication atmosphere has significant effects on the film texture and defects.As the increase of the oxygen pressure of annealing atmosphere,the Pb_(2)Bi_(4)Ti_(5)O_(18)films show a preferred growth orientation of(00l)and fewer defects,which leads to a higher polarization and breakdown field for the film annealed in air atmosphere and thus help to achieve an ultrahigh energy density of59.4 J·cm^(-3)and an improved efficiency of 81.2%.Moreover,the film also exhibits excellent cycling reliability and good thermal stability.The Pb_(2)Bi_(4)Ti_(5)O_(18)films show a significant potential application for dielectric capacitors.