Surface characterization and diffusion model of pack borided TB2 titanium alloy

Abstract

In this work, TB2 alloy was successfully borided by pack boriding at the temperature range of 950–1100 °C for 5, 10, 20 and 30 h. The characteristics of boride layers were examined by X-ray diffraction, scanning electron microscopy, wavelength dispersive spectrometer, microhardness tester and micro vibration friction and wear tester. Based on the diffusion models of d2 = Dt and d = kt0.5, growth kinetics of the boride layers on TB2 alloy were investigated via the thickness of boride layers. There are dual boride layers on the surface of borided TB2 alloy, i.e. the outer TiB2 layer and the inner TiB layer. The microhardness and coefficients of friction (CoF) of borided TB2 alloy at 1100 °C for 30 h can reaches ~ 27.5 GPa and ~ 0.35, respectively. The diffusion model of d = kt0.5 is found to predict the thickness of boride layer more accurately. Therefore, the boron activation energies in TiB layer and TiB2 layer are 96.220 and 158.056 kJ mol−1, respectively. Finally, a comparison between the present boron activation energies and the reported available data was also made.