Characterization and growth kinetics of boride layers on Ti-5Mo-5V-8Cr-3Al alloy by pack boriding with CeO2

Pack boriding with CeO2 experiments were performed on the beta-type Ti-5Mo-5V-8Cr-3Al alloy (TB2 alloy) using boriding powder at the temperature of 950-1100 degrees C for 5-30 h. The boride layers characteristics were investigated by means of X-ray diffraction, scanning electron microscope, electron probe microanalysis, high resolution transmission electron microscope, and microhardness and wear tests. The results showed that two layers, including the outer TiB2 layer and the inner TiB layer, can be found in the boride layers. The TB2 alloy pack-borided with CeO2 at 1100 degrees C and 30 h have microhardness of 28 GPa and coefficient of friction of 0.282. The growth kinetics of TiB and TiB2 layers obey the diffusion model of d = kt(0.5). The activation energies of boron in TiB and TiB2 layers during the pack boriding with CeO2 are 91.539 kJ/mol and 146.825 kJ/mol, respectively.