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

Abstract

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 9008C for 1 h in vacuum and finally quenching. The austenite transformation temperature of the prepared shape memory alloy was found to be ,2088C. Thus, the developed process enables to curtail the long milling time as well as decrease the prolonged homogenisation treatments.

Differences of the microstructural evolution of Cu powder during continuous and interrupted mechanical milling

“…Therefore the presence of oxygen in the MM system could affect severely the chemical, physical and mechanical properties of the final product [9,[11][12][13][14]. Parameters such as milling time, process control agent or the choice of a continuous or interrupted cycle determine the characteristics of the milled powders and the level of oxygen absorbed [15,16]. For all these reasons this study has been carried out by subjecting commercially atomised copper powder to planetary MM for different times and different type of milling cycle.…”