超弹性NiTi合金丝激光点焊接头的组织和性能

Microstructures and properties of laser spot-welded joint of superelastic NiTi alloy wire

采用脉冲激光焊研究了Ti 50.6%Ni(摩尔分数)合金细丝点焊, 对比分析了接头与母材显微组织、相变行为、Ni含量、显微硬度及应力—应变曲线的变化。结果表明: 当 NiTi合金用做功能材料时, 激光焊接是可取的; 激光点焊接头熔化区由树枝晶组成, 热影响区靠近熔池部分为粗大等轴晶, 靠近母材部分为细小等轴晶; 激光焊会造成Ni的蒸发, 使接头中Ni含量降低0.2%(摩尔分数), 从而影响接头的相变行为; 接头抗拉强度可达母材的70%, 可恢复应变达母材的92%。

Ti-50.6%Ni(mole fraction) wires were welded using pulsed YAG laser. The laser spot-welded joints were tested for the microstructure, transformation behavior, Ni-content, micro-hardness and stress—strain curves in comparison with the base metal. The results show that laser welding NiTi alloy is advisable when NiTi alloy is used as functional materials. The fusion zone features dendrite structure, the microstructures of heat-affected zone can be divided into two parts, i.e. coarse equiaxial crystals near the fusion zone and fine equiaxial crystals near the base metal. The transformation behavior of the joint is affected by the vaporization of Ni during the laser welding process. The ultimate tensile strength of the joint is up to 70% of the base metal, the maximum recoverable strain is up to 92% of the base metal.