Ni47 Ti44 Nb9合金丝氩弧焊接头的显微组织和力学行为

系统研究了Ni47Ti44Nb9宽滞后记忆合金带氩弧焊点丝材的显微组织和力学行为.结果表明,焊后适当温度退火处理可显著改善焊点的显微组织,得到细小、均匀的等轴晶,从而提高了焊点的力学性能,室温下表现出较高的拉伸强度和延伸率.焊后未经退火处理的试样,室温拉伸断口均位于焊缝金属的熔合区内,微观断口存在明显的解理台阶,为典型脆性断裂.退火处理后,断口位于近焊缝处的热影响区内,是韧窝型断口,属塑性断裂.韧窝内镶嵌有(Ti,Nb)2Ni相,该相内部及其与基体交界处存在有明显的微裂纹.带焊点丝材经退火处理后在---60℃下变形,最大弯曲可恢复应变约为5%,表明焊点处仍具有一定的记忆效应.

Microstructure and mechanical behaviors of TiNiNb wide hysteresis shape memory alloy wire argon arc welding joint

The microstructure and mechanical behaviors of TiNINb wide hysteresis shape memory alloy (SMA) argon arc welding joint have been systematically investigated in the present paper. The experimental results show that the microstructure of the welding point can be changed to the fine and uniform equiaxed grains by the proper annealing treatment, resulting in the excellent mechanical behaviors of the welding joint. At the ambient temperature, the tensile strength and elongation of the welding joint after proper annealing are relatively high. For the welding joint without annealing, the fraction occurs in the fusion area of the welding point during the tensile process, and obvious cleavage steps have been observed in the fracture, implying that the break is brittle. Wheras for the welding joint after annealing, the crack occures in the heat affected zone (HAZ), and dimples are observed in the fracture, suggesting that the fracture is ductile. (Ti,Nb)_2Ni particles are found at the bottom of the dimples. And obvious mico-cracks exist in both the interior of the particles and the interface betweent the (Ti,Nb)_2Ni particle and the matrix. The maximum recoverable strain of the TiNiNb SMA wire with welding joint after annealing is about 5%, indicating that the welding point remains some shape memory effect.