采用Nd:YAG激光和光纤激光焊接了Ti-50.7%Ni(原子分数)记忆合金, 利用DSC, SEM和EDS对焊缝金属相变温度的变化规律和影响因素进行了分析, 并对焊接接头的记忆功能进行了研究. 结果表明, 不同焊接工艺参数的焊缝金属与母材相比,相变温度有明显差异, 产生差异的主要原因是组织的不同和基体Ni含量的差别. 基体Ni含量与C, O, N的含量、富Ni沉淀相尺寸和数量以及焊接过程中Ni的烧损有关.低热输入、高激光功率密度的焊缝金属, 基体Ni含量高, 相变温度偏离母材的程度更大.焊缝金属相变温度的变化使得焊接接头形状恢复温度区间明显不同于母材, 对其使用性能产生不利影响.
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.
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