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 hipping facility under a range of process conditions. Detailed microstructural characterisation indicated that pressure nitriding produces a compound TiN–Ti2 AlN layer on the alloy surface. The growth of these titanium rich nitrides results in the formation of an aluminium rich, single phase γ-TiAl diffusion layer immediately below the compound layer. Partitioning of the alloying elements (Mn and Nb) is observed in the region immediately below the compound layer. The presence of a thin (<0·5 μm) layer of AlN has been identified on the surface of as nitrided specimens. The influence of process parameters on the growth rate and morphology of the compound layer has been determined. The compound layer formed on Ti–45Al–2Mn–2Nb+ 1 at.-%TiB2 was generally thinner than that formed on Ti–48Al–2Mn–2Nb following nitriding under identical conditions.