TiNi形状记忆合金与不锈钢激光焊接头裂纹分析及防止措施

采用激光焊对TiNi形状记忆合金与不锈钢异种材料进行焊接,用扫描电镜和激光共聚焦显微镜研究了TiNi合金/不锈钢接头裂纹及断口特征,分析了焊缝裂纹的形成机理,并提出了防止裂纹的措施.结果表明,裂纹多以微裂纹的形式出现于焊缝中心和TiNi合金侧熔合区.焊缝中存在大量的脆性化合物是产生裂纹的内在原因,接头受到拉伸应力是产生裂纹的必要条件,焊缝裂纹是二者共同作用的结果.通过焊接区加镍和钴中间层材料、改变激光光斑位置、焊接区施加轴向力及优化激光焊接参数的方法均能在一定程度上改善焊缝金属的裂纹敏感性,其中加金属中间层效果更为明显,加镍和钴中间层后,接头抗拉强度分别达到372和347 MPa,比未加中间层的接头的抗拉强度分别提高98.9%和85.6%.

Analysis and prevention of cracks in laser-welded joint of TiNi shape memory alloy and stainless steel

Dissimilar metal joints of TiNi shape memory alloy wire and stainless steel wire were welded by laser welding method.The cracks feature and fracture surface morphology of joints were examined by using scanning electron microscopy(SEM) and confocal laser scanning microscope(CLSM).The mechanism of crack formation were analyzed, and some measurenents were taken to control the welding cracks.The results showed that the micro-cracks usually emerged in the center of the weld zone and fusion zone of TiNi alloy side.The existence of a large number of brittle compounds in the weld was internal cause of cracks, and the joint subjected to tensile stress was the necessary condition of cracks.The cracking susceptibility can be improved to a certain extent by adding Ni interlayer, Co interlayer, changing the laser beam position, applying an axial force to weld zone and optimizing the laser welding parameters.Adding metal interlayer was a more effective method.The tensile strength reached 372 MPa and 347 MPa respectively by using Ni and Co interlayer, and the joint strength increased by 98.9% and 85.6% respectively, compared with the joint without metal interlayer.