Ti-Ni系形状記憶合金およびその接合部の特性と破面形態

概要

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Mechanical properties and fracture behaviour of Ti-50.7at%Ni shape memory alloy and its laser weld joint have been investigated. The base metal aged at 673 K for 3.6 ks exhibited super elasticity and higher tensile strength than the solution base metal. However, the aged material showed less fracture strain and more brittle fracture surface than the solution material. Butt welding of 3 mm thick Ti-Ni alloy was performed using 10kW CO_2 laser. The laser welded specimens showed a successful shape memory effect and super elasticity. These properties were identical with those of the base metal. However, the tensile strength and the fracture strain of the laser welded specimen were less than those of the base metal. The fracture occurred at the columar crystal boundary at the center of the weld metal. The boundary was perpendicular to the direction of the loading and, moreover, oxide inclusions crystallized at the boundary. These facts seem to cause low strength of the weld joint. The fracture strain of the welded specimen, nevertheless, was more than 6 % which is the maximum recoverable elongation in polycrystal Ti-Ni base metal. Laser weld is, therefore, applicable to the joining of Ti-Ni shape memory alloy when the alloy is used as a functional material.
社団法人日本材料学会の論文
1989-05-15