Laser nitriding of pure titanium with Ni, Cr for improved wear performance

Titanium and its alloy suffer from galling, seizing, ploughing and adhesion during sliding contacts. A laser nitriding method to improve the tribological properties of pure titanium was investigated in this study. Before laser nitriding, a layer of nickel and chromium was plasma sprayed onto the surface of pure titanium in order to prevent the formation of cracks and pores during laser treatment. A scanning electron microscope (SEM) and image analyser were used to optimize the laser processing parameters and analyse the coating microstructure. X-ray diffraction (XRD), a Talysurf 5 tester and microhardness tester were used to analyse the phase crystallinity, surface roughness and micro-hardness of the laser treated coating. A ball-on-flat reciprocating wear machine was used to evaluate the sliding and fretting wear behaviours of both untreated and laser treated specimens. Results showed a substantial improvement in wear resistance after laser treatment which can be attributed to a significant improvement in hardness and corrosion resistance as well as a decrease in friction properties of nitrided layers.