Microstructure and wear properties of powder-pack borided Ti–5Al–2.5Sn alloy

The boride layer was prepared on the surface of Ti–5Al–2.5Sn alloy by powder-pack borided at 975–1075 °C for 20 h with a temperature interval of 25 °C, and surface morphology, phase composition, microstructure, hardness, and wear properties of the borided Ti–5Al–2.5Sn alloy were investigated. The crystal parameters of TiB2 phase in the boride layer at different boriding conditions were obtained from the Rietveld structure refinement of Ti–5Al–2.5Sn samples, and the theoretical hardness values of TiB2 were calculated using the first-principles calculations. The results indicate that the boride layer comprises the outer TiB2 layer and the inner TiB whisker, and TiB2 layer thickens and TiB whiskers coarsen with the increase of temperature. The hardness of TiB2 layer is related to the boriding temperature, the greater hardness of TiB2 layer corresponds to the higher boriding temperature, which is in good agreement with the theoretically predicted results. Ti–5Al–2.5Sn alloy borided at 1075 °C–20 h has the highest hardness and excellent wear resistance. Finally, wear mechanisms were also discussed, which is a combination of abrasive and adhesive wear.