The effect of alloying elements in Ti-5Mo-5V-8Cr-3Al alloy on growth kinetics of TiB whiskers in boride layer

As one of the important ways to improve surface properties of Ti alloys, the boride layer prepared by the pack boriding is closely related to the growth and morphology of TiB whiskers in the boride layer, whereas the growth and morphology of TiB whiskers are significantly affected by alloying elements in the alloys. This work systematically explored the effect of alloying elements in β-type Ti-5Mo-5V-8Cr-3Al Ti alloy on growth kinetics of TiB whiskers and thickness of the boride layer using experiment and first-principles investigations. After boriding, an outer TiB2 layer and an inner TiB whisker + Ti layer are formed on Ti surface. TiB/β-Ti interface herein is non-coherent with the orientation relationships of (0 1 1)TiB//(1¯1¯ 0)β-Ti and [1¯ 00]TiB//[1¯ 11]β-Ti. Alloying elements segregated at the interface can increase diffusion energy barrier and slow down diffusion rate of active [B] atoms, and further reduce growth rate of TiB whiskers. Finally, a theoretical model for the boride layer growth on Ti surface was proposed.