LASER SURFACE MELTING OF TI-6AL-4V ALLOY

Surface hardening of Ti-6Al-4V alloy with laser surface melting (LSM) in a nitrogen atmosphere has been studied. In LSM, hardness increased almost three-fold in comparison to that of the substrate, the latter having a Vickers hardness of 350, by the formation of TiN in the range of 100-mu-m of melt depth. Hardness, then, decreased slowly and reached a minimum of 580 VHN at a maximum melt depth of 750-mu-m. Alpha'-Ti was formed in the heat-affected zone (HAZ) with a VHN of 450. Ageing treatments were performed for all specimens at 450-degrees-C and different ageing times (1-20 h). Short ageing treatments increased the hardness in the melted zone as well as in the HAZ (1-3 h). Long ageing treatments (7-20 h) resulted in uniform hardness distribution in the melted zone.