Effect of heat treatment on microstructure and mechanical property of Ni-42Ti-8Al alloy

Effects of heat treatment on microstructure and mechanical property of Ni-42Ti-8Al alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and compressive test. The results show that the microstructure of as-cast Ni-42Ti-8Al alloy is composed of NiTi matrix and reticular eutectic structure around the grain boundaries, which is composed of NiTi and Ni₂TiAl phase. Fine Ni₂TiAl particles with regular arrangement are coherent or semi-coherent with NiTi matrix, causing precipitation strengthening effect. When the alloy is treated by solid solution at 1090°C for 5 h, most eutectic structure is dissolved, and the precipitate around the grain boundaries again after aging treatment at 600°C for 26 h. For aging at 700°C, the eutectic structure is distributed more dispesively. The compressive yield strength at high temperatures firstly increases and then decreases with rising aging temperatures. For Ni-42Ti-8Al alloy, an optimal aging temperature of 700°C is obtained. When aging temperature is over or under 700°C, the strength of the alloy is reduced.