Surface modification of Ti-6Al-4V alloy by pack boronizing

A pack boriding technique was employed to obtain a hard coating on the surface of Ti-6Al-4V alloy in this paper. The diffusion process was carried out at various temperatures ranging from 1000°C to 1100°C for 5 to 20 hours. The microstructure, morphology and the phase composition of Ti-6Al-4V alloy after boriding were investigated. The diffusion behavior of Ti, Al, V, B elements in boronizing process was also discussed. The results showed that the thickness of diffusion layer ranged from 0.8 μm to 15 μm for different boriding parameters. The biphasic boron-titanium compounds TiB-TiB2 layer have formed on the surface of Ti-6Al-4V alloy. The XRD results of surface layer revealed that the amount of TiB and TiB2 increased with temperature rising. Furthermore, the surface B atoms reacted with Ti of Ti-6Al-4V matrix that led to the reduction of Ti in transition region. The microhardness value of TiB2 to TiB was gradient distribution ranged from 2200 HV0.01 to 1100 HV0.01. And the hardness value in the transition region was higher than the Ti-6Al-4V matrix.