Surface modification of TiAl based intermetallics by pressure nitriding

Two TiAl based intermetallic alloys, Ti-48Al-2Mn-2Nb and Ti-45Al 2Mn-2Nb 1 at.-%TiB2, were nitrided at high-gas pressures using a conventional hippi ng facility under a range of process conditions. Detailed microstructural c haracterisation indicated that pressure nitriding produces a compound TiN-T i2AlN layer on the alloy surface. The growth of these titanium rick nitride s results ill the formation of an aluminium rich, single phase gamma-TiAl d iffusion layer immediately below the compound layer. Partitioning of the al loying elements (Mn and Nh) is observed in the region immediately below the compound layer. The presence of a thin (<0.5 mu m) layer of AlN has been i dentified on the surface of ns nitrided specimens. The influence of process parameters on the growth rate and morphology of the compound layer has bee n determined. The compound layer formed on Ti-45Al-2Mn-2Nb + 1 at.-%TiB2 wa s generally thinner than that formed on Ti-48Al-2Mn-2Nb following nitriding under identical conditions.