Friction and wear of unlubricated copper-based CuZnAl shape memory alloys

Abstract

Experiments of unlubricated friction and wear have been carried out on nominal Cu-26Zn-4Al (wt.%) shape memory alloy (SMA) against steel using block-on-ring geometry with a sliding speed of v = 0.52 m s /t-1, distance S = 93.4 m, and normal load P=5–100 kg. Scanning electron microscopy has been utilized to study worn surfaces and debris. It reveals that the wear of CuZnAl alloy was plasticity dominated, with adhesion and delamination being the two main mechanisms. Wear results show that CuZnAl specimens in martensite exhibiting shape memory effect (SME) on average behave in a more weatherproof manner than those in the β phase exhibiting superelasticity. However, both are more wear durable than the same materials in forged conditions. Transmission electron microscopy observation of tensile tests on CuZnAl thin crystals in the β phase showed that stress-induced martensitic transformation occurred from the β phase in the vicinity of pre-existing microcracks on the foil during tensiling. The authors proposed the blunt mechanisms of crack tips due to preferential orientation reactions of variants in martensite and stress-induced martensitic transformation in the β phase to explain the nature of the wear of CuZnAl SMA.