Effects of Co2 and Nd:YAG Laser Remelting of the Ti6Al4V Alloy on the Surface Quality and Residual Stresses

Abstract The titanium alloys are materials susceptible to tribological wear and the laser treatment can be applied in surface treatment processes to obtain for example higher hardness level. From the other side, it is important to take into consideration, that hardness increase that can be connected with cracks. The aim of this research was to investigate the effects of different lasers and the process parameters on the form and level of residual stresses in the Ti6Al4V alloy, which determine the initiation and propagation of cracking. Two lasers were used, the CO 2 and Nd:YAG lasers. The specimens were remelted in liquid nitrogen, water or calm air at different pre-heating temperature. The different laser power and scan rates were applied. The increase in energy density increased the number of cracks, the change of an environment and pre-heating affected alo the surface cracking. The cracks observed after remelting with Nd:YAG laser were longer than those observed after treatment with CO 2 laser. The compressive stresses after the CO 2 laser treatment, and tensile stresses after treatment with the Nd:YAG laser, were found. The appearance of cracks was attributed to an excessive energy density. The different distribution of heat energy inside and around the laser tracks was discussed as the origin of presence either tensile or compressive stresses in the alloy treated with different lasers.