Wear rate at RT and 100oC and operating temperature range of Cu50Zr50 shape memory alloy controlled through microalloying

Wear rate at RT and 100oC and operating temperature range of Cu50Zr50 shape memory alloy controlled through microalloying

1Younes, A., 1Nnamchi, P., 2Medina, J., 2Pérez, P., 1Villapún, V.M., 3Badimuro, F., 4Kamnis, S., 5Jimenez-Melero, E., 1*González, S.
*lead presenter
1sergio.sanchez@northumbria.ac.uk, Northumbria University, UK
2 Centro Nacional de Investigaciones Metalúrgicas, Spain
3 University of Leeds, UK
4Monitor Coatings, UK
5 University of Manchester, UK
Abstract:
Introduction: The effect of microalloying with Co on the tribological performance and operating temperature range of Cu50Zr50 shape memory alloy against 304 stainless steel counterface has been investigated by performing pin on disc tests and studying the wear behaviour and evolution of mass loss of Cu50Zr50, Cu49.5Zr50Co0.5 and Cu49Zr50Co1 at. % at RT and 100oC. For tests conducted at RT, microalloying with Co0.5 at. % appeared to have maximum wear resistance due to the effect of Co in promoting stress-induced martensitic transformation through lowering Stalking Fault Energy (SFE). For wear tests conducted at 100oC for 1 hour, higher mass loss values were attained than for RT tests since hard martensite partly reverts into soft austenite though an isothermal process. Additionally, at higher temperature, the alloys are more prone to oxidation therefore developing a thick brittle oxide layer that can easily get fragmented and detached, thus promoting even higher mass loss compared to RT alloys. The effect of microalloying with Co in promoting martensitic transformation is negligible when testing at 100oC for 1 hour, since martensite partly reverts into soft austenite and develops a thick oxide layer gets easily detached.

Summary: The evolution of mass loss of Cu50Zr50, Cu49.5Zr50Co0.5 and Cu49Zr50Co1 at. % at. RT shows that microalloying with Co0.5 at. % promotes martensitic transformation the most thus resulting in maximum wear resistance. However, when wear testing at 100oC for 1 hour, the wear resistance decreases due to the effect of isothermal process in partly reverting hard martensite into soft austenite, in addition, it promotes the formation of thick oxide layer that gets fragmented and detached easily.

Result: Results show that microalloying with Co to promote martensitic transformation is only valid within a temperature range, above that range, the effect of isothermal process partly transforms martensite into austenite and decreases the wear resistance.