Ion nitriding of titanium aluminides with 25–53 at.% Al I: Nitriding parameters and microstructure characterization

Abstract

Titanium aluminides with Al contents of 25, 40, 50 and 53 at.% were ion nitrided to modify the surface conditions. The effects of four process parameters, namely nitriding temperature, nitriding time, working pressure and [N 2] [H 2] ratio, were investigated by the orthogonal test. The phases and microstructures of the nitrided surface were studied by X-ray diffraction (XRD), electron probe microanalysis, optical microscopy and scanning electron microscopy. Experimental results indicate that nitriding temperature and time are the primary parameters responsible for improving surface hardness. The nitrided compound layer consists of TiN and Ti 2AlN phases. As the Al content in titanium aluminides increases, the XRD intensity of Ti 2AlN phase becomes stronger. The diffusion layer in all the cases has little nitrogen, allowing this layer to be easily attacked by the etching reagent. A mechanism to explain the formation of the ion-nitrided layer in titanium aluminides is also proposed in this study.