Microstructure investigation of new iron-based FeNiCoAlTiNb shape memory alloys

The microstructure of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) polycrystalline alloy was investigated for this study. The homogeneous heat treatment condition is 1277 ​°C for 24 ​h. When the heat treatment temperature is above 1300 ​°C, second phases generate along the grain boundary and contain high Ni, Al, Ti, Nb and low Fe and Co element compare to nominal composition. From the aging heat treatment results, the size of precipitates is around 5–10 ​nm when the sample is aged at 600 ​°C for 72 ​h. From the thermo-magnetization results, the saturation magnetization is 140 emu/g. The magnetization loop is shifted to higher temperature when the aging times increase from 24 to 96 ​h. The result indicates that the transformation temperature tends to increase with increasing the aging times.