Characterization and diffusion model for the titanium boride layers formed on the Ti6Al4V alloy by plasma paste boriding

The present study is focused on the estimation of activation energy of boron in the plasma paste bonded Ti6A14V alloy, which is extensively used in technological applications, using an analytical diffusion model. Titanium boride layers were successfully produced by plasma paste bonding method on the Ti6A14V alloy in the temperature range of 973-1073 K for a treatment time ranging from 3 to 7 h. The presence of both TiB2 top-layer and TiB whiskers sub-layer was confirmed by the XRD analysis and SEM observations. The surface hardness of the bonded alloy was evaluated using Micro-Knoop indenter. The formation rates of the TiB2 and TiB layers were found to have a parabolic character at all applied process temperatures. A diffusion model was suggested to estimate the boron diffusivities in TiB2 and TiB layers under certain assumptions, by considering the effect of boride incubation times. Basing on own experimental data on bonding kinetics, the activation energies of boron in TiB2 and TiB phases were estimated as 136.24 +/- 0.5 and 63.76 +/- 0.5kJ mol(-1), respectively. Finally, the obtained values of boron activation energies for Ti6AI4V alloy were compared with the data available in the literature. (C) 2016 Elsevier B.V. All rights reserved.