Tribological performance of plasma nitrided gamma based titanium aluminides

Ti–48Al–2Nb–2Mn (at.%) alloy was plasma nitrided to investigate the effect of this thermochemical surface modification on the tribological behaviour of gamma based titanium aluminides. The effects of nitriding temperature, nitriding time and H2/N2 gas ratio were investigated. Characterisation of the microstructure and phases formed within the nitrided surface layers was performed using optical and electron microscopy, X-ray diffraction (XRD) and glow discharge spectroscopy (GDS). The wear resistance of the plasma nitrided samples increased considerably against ball bearing steel (AISI 52100). Experimental results indicated that time controls the thickness and nitriding temperature, and H2/N2 ratio is responsible for the crystal structure of the nitrided layers. The nitrided compound layers consist of TiN and Ti2AlN phases. The diffusion zone, in most cases comprises of recrystallised gamma grains beneath the compound layer.