预置填充稀土激光焊接对TiNi形状记忆合金功能性的影响

Effect of Laser Welding of Preset Rare Earth to the Welded Joint on the Functional Properties of the Ti-50.9at% Ni Shape Memory Alloy

采用Nd-YAG连续激光器对2mm厚Ti-Ni50.9at%形状记忆合金进行焊缝预置填充材料激光焊接,预置填充材料是通过熔炼方法制备的添加2%(质量分数)稀土元素La和Ce的与母材同等原子比的TiNi合金。对形状记忆合金母材及焊缝(无填充稀土与填充稀土)的马氏体相变行为、机械性及超弹性进行了对比研究。利用差热分析仪(DSC)测试焊缝及母材的马氏体相变及温度;通过应力-应变拉伸测试母材及焊缝的机械性能及超弹性。结果表明:由于填充稀土,使TiNi形状记忆合金马氏体相变温度Ms和终了温度Mf提高,同时使马氏体向奥氏体转变的起始温度As和终了温度Af提高,奥氏体的相变区间缩小;填充稀土焊接接头的抗拉强度比无填充稀土焊接接头有明显提高,填充稀土焊接接头试样断裂前可以承受比母材更大的变形;填充稀土激光焊缝呈现较好的超弹性。

Rare earth elements （RE） La and Ce of 2wt% were added into the Ti-50.9at% Ni shape memory alloy prepared by fusion metallurgy method to obtain filling material, and it was preset to the butt joint of 2 mm thick tapes of the same atom-ratio TiNi alloy welded by Nd-YAG continuous laser-welding machine. The martensitic transformation behaviours, mechanical properties and the pseudoelasticity of the two different welded joint （with RE earth and without RE earth） were investigated through a systematic comparison The martensitic transformation behaviour can be measured by the differential scanning calorimeter （DSC）. The mechanical properties and the pseudoelasticity of laser welded samples both with RE and without RE were tested at the specific temperature by stress-strain measurements. The results show that, RE addition in the laser-welding joint can increase the martensitic transformation starting temperature Ms and finishing temperature Mf and the motransformation ,As and Af, reducing austenite transformation interval. The strength of extension of the welded joint with RE is increased apparently compared with that without RE. It also can receive larger deformation before abruption than parent material and presents better pseudoelasticity.