WEAR AND FRICTION BEHAVIOUR OF TITANIUM-NICKEL SHAPE MEMORY ALLOYS

摘要

Pure Ti100, Ti48Ni52 and Ti52Ni48 shape memory alloys (SMAs) are produced by powder metallurgy (PM) method at 1100 C for 5 h and microstructures are examined by optical microscope. Dry wear behaviours of SMAs are investigated through the pin-on-disc type wear testing machine under. different conditions. Also, friction coefficients are measured during the course of wear. Microscopic examination indicates that there are small pore sizes and regular pore formations in pure titanium, but large sizes of porosity distributions with irregular pore formations are observed for NiTi shape memory alloys (SMAs). The distribution of pores seems to be more uniform for the titanium than those of SMAs. Some porosities observed for Ti48Ni52 SMA have not regular shapes and its sizes are bigger than that of titanium. However, there are not many differences between these SMAs. Hardness increases with adding Ni content to the Ti matrix. Increases in hardness are about 38% for NiTi shape memory alloy. In addition, it is found that the average volumetric wear rate increases linearly with increasing load. The change is small for the SMAs, but there are big differences between the matrix and SMAs because of microstructure and hardness. Furthermore, coefficient frictions of pure titanium are found to be about 0.32 for 20 N, but it increased up to 0.42 with increasing load. Friction coefficients of NiTi alloys are bigger than that of the titanium while no significant differences are observed between them. However, large fluctuations are observed in friction coefficients with increasing the load due to ductility and wear scar width associated with porosity.