NiTi Shape Memory Alloy at the Nanoscale Regime Prepared by Mechanical Alloying and Subsequent Annealing at Low Temperature

摘要

A full amorphous NiTi shape memory alloy (SMA) was successfully prepared by mechanical alloying (MA) technique from elemental Ti and Ni powders, at very short milling time of 8 hours. This MA time is the shortest amorphization reaction reported on this system so far. X-ray diffractometer and scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) have been used to follow the structural changes of the amorphization reaction. At this short MA time, no contamination from the milling tools was detected. Annealing at 352 ℃ for relatively short time of 50 minutes resulted in the complete transformation of the amorphous NiTi phase into a B2-NiTi crystalline phase. This is a very low temperature to obtain this phase compared with any conventional methods. More importantly is that the obtained phase is in the desirable nanoscale regime, where crystallite sizes are easily controlled by annealing.