Effect of milling parameters on processing, microstructure and properties of Cu-Al-Ni-Ti shape memory alloys

The effect of milling parameters, such as ball/powder ratio (BPR), milling speed and time, on the microstructural and phase development of powder metallurgy processed Cu–Al–Ni–Ti shape memory alloys has been studied. It has been found that milling for 40 h at a BPR of 40:1, 200 rev min-1 is the optimised condition for mechanical alloying in an attritor mill in order to get a uniform distribution of the alloying elements. A lower BPR caused insufficient milling, whereas a higher BPR led to oxidation of the powder. The complete formation of martensite occurred in the sample prepared under the optimised milling condition followed by cold compaction, sintering at 900°C for 1 h in vacuum and finally quenching. The austenite transformation temperature of the prepared shape memory alloy was found to be ∼208°C. Thus, the developed process enables to curtail the long milling time as well as decrease the prolonged homogenisation treatments.