EFFECT OF LASER WELDING PARAMETERS ON THE TRANSFORMATION TEMPERATURE OF TiNi ALLOY

Nd:YAG laser and fiber laser were employed to weld Ti-50.7%Ni (atomic fraction) alloy, the effects of laser welding parameters on phase transformation temperatures, microstructure and chemical composition of weld metals were investigated by using DSC, SEM and EDS. The results show that phase transformation temperatures of base metal and weld metal are much different, and the start recovery temperature of weld joints are lower about 40 than that of base metal. Such difference is resulted from the changes of microstructure and Ni content in the matrix, which is related to the contents of element C, O and N, the size and quantity of Ni-riched precipitate, as well as the burning loss of Ni during laser welding. Laser welding with low heat input and high laser power density results in big difference of phase transformation temperature due to the high content of element N and O, small size and quantity of precipitate, little burning loss as well as the high Ni content in the matrix.