Structure and tribological properties of post-sputtered annealing nickel titanium alloy coatings onto 316l stainless steel.

Abstract

The purpose of this study is to investigate the effect of the post-sputtering annealing process on the structure and tribological properties of the NiTi shape memory alloy (SMA) coatings. The NiTi SMA coatings were deposited onto the 316L stainless steel substrates using the sputtering PVD technique. The coating thickness was measured at approximately 2µm. The unannealed NiTi SMA coating was determined amorphous based on the differential scanning calorimetry (DSC) and XRD results. The crystallization temperature of the NiTi SMA coating with a composition of Ni 57.89%:Ti 42.11% was determined at a temperature of 519.23°C by the DSC. The post-sputtering annealing process was carried out at the annealing temperatures of 550°C and 600°C and the annealing times for a duration of 30 and 60 minutes. The unannealed and annealed NiTi SMA coatings were then characterized to determine their structure and mechanical properties using various characterization techniques namely optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), surface roughness tester, Rockwell C adhesion test, pin-on-disc wear test and nanoindentation test. The post-sputtering annealing process was successful in producing a crystalline Ni-rich NiTi coating with excellent mechanical properties. In this study, the annealing temperature of 600°C for a period of 30 minutes provided the optimum adhesion and mechanical properties of the annealed NiTi SMA coatings. The finding shows the potential of the post-sputtering annealing process to create an excellent structure and tribological properties of NiTi SMA coatings.