Effect of Plasma Surface Niobizing of γ-TiAl Alloy on Wear Resistance

Niobium alloying of gamma-TiAl has been of great interest in resent years because of its better oxidation resistance. But for the application of TiAl in automobile or aircraft engine components, the wear resistance is very important. In this work, a Nb-alloyed layer, about 20 mu m in thickness, was formed in the surface of gamma-TiAl. The alloyed layer was composed of Nb2Al and Nb3Al. The hardness of the induced surface layer was about 600HV, higher than untreated TiAl. The optical microscopy and scanning electronic microscopy were used to observe morphology of the surface and cross section of plasma alloyed TiAl; the chemical composition of the surface layer was examined by glow discharge spectrum; the hardness was measured using micro-hardness tester with the Koop values. Untreated and alloyed TiAl samples were subjected to dry sliding wear against steel counter ball and their tribological response was studied. A ball-on-disk type apparatus was used. Volume loss measurements were done to determine the wear rate. Immediately after the tests, the wear scar was examined microscopically. The result shows that the surface alloyed layer of TiAl has a graded distribution of the hardness value and the wear rate is less than the untreated TiAl. In other words, the plasma alloying of niobium can increase the wear resistance of TiAl alloy.