Analysis of in situ gas nitriding by dilatometry of porous Ti6Al4V materials

Gas nitriding was used to coat highly porous compacts of Ti6Al4V alloy, and in this work, for the first time, the nitrogen diffusion process was evaluated by means of dilatometry tests. Nitriding was performed between 950 and 1250 °C with a dwell time of 1 h, and the axial deformation was measured during the whole thermal cycle. Coating thickness was estimated from SEM micrographs. Results indicate that coating thickness can be determined as a function of the axial deformation that follows a power law, which is based on the two spheres model. TiN phase is obtained above 1100 °C; meanwhile, using lower temperatures, Ti2N is the major component of coating. The gain of mass increased linearly with respect to the increment of the nitriding temperature. The main conclusion of this work is that TiN coating can be homogenously formed over the surface of the inner porosity of a sample and the thickness can be estimated by the axial deformation undergone by the whole sample.