Wear rate at RT and 100 °C and operating temperature range of microalloyed Cu₅₀Zr₅₀ shape memory alloy

The effect of microalloying with Co on the wear rate and on the operating temperature range of Cu₅₀Zr₅₀ shape memory alloy against 304 stainless steel counterface has been investigated by studying the mass loss and wear behaviour of Cu₅₀Zr₅₀, Cu_49.5Zr₅₀Co_0.5 and Cu₄₉Zr₅₀Co₁ at. % at room temperature (RT) and 100 °C. For the alloys tested at 15 N, maximum wear resistance is achieved at RT for the alloy with 0.5 at. % Co compared to the parent Cu₅₀Zr₅₀ at. % alloy. This is mostly attributed to the effect of Co in promoting stress-induced martensitic transformation (i.e., work-hardening). For wear tests at 100 °C (100 °C plus friction temperature for 1 h), the mass loss is higher than that at RT since martensite partly reverts into soft austenite through an isothermal process. In addition, the alloys are more prone to oxidation with formation of thick oxide layers that can easily get fragmented and detached from the surface thus resulting is higher mass loss than at RT. The effect of Co in promoting martensitic transformation is negligible when testing at 100 °C, since the stress-induced martensite partly reverts into austenite and the thick oxide layer formed on the surface not only masks the effect of the underlaying substrate for it can also easily detach upon wear.