냉간압연에 의해 제조된 Ti-Ni계 합금 리본의 마르텐사이트 변태 및 형상기억 특성

Abstract

Recently, Ni-rich Ti-Ni binary alloy has been widely used as an actuator in automobile and medical industries. In this study, this binary alloy was cold-rolled and annealed at the temperatures, 250, 350, 450 and 550℃ to evaluate mechanical property, microstructural change, martensite transformation and shape memory effect.

(1) The hardness value of the ribbon rolled to 65% was 325.6 Hv, and the hardness value of the as-received wire was 211Hv. As the degree of processing increased, the hardness value increased. Also as the annealing temperature increased, the hardness value decreased.

(2) In the rolled ribbons, B2 → R-phase → B19' forward transformation during cooling and B19' → B2 reverse transformation during heating did not appear. But as the annealing temperature increased, B2 → R phase → B19' and B19' → B2 transformations appeared, and R-phase disappears and B2 ↔ B19 'transformations appeared.

(3) The as-received wire does not appear deformation band and the deformation band was most prominent at 65%. The shape of the deformation band was appeared to difference according to the degree of processing. Also as the annealing temperature increased, the deformation band disappeared and the ribbon with the 65% processing degree had a residual deformation band.

(4) The martensite plate of the processed ribbon was finer than the as-received wire martensite plate. The martensite structure with the degree of processing of 65% was the finest, and the martensite structure was observed as the annealing temperature increased.

(5) In as-received wire, R-phase → B19' martensite transformation occurred even without annealing. But phase transformation characteristic did not appear in the rolled ribbon. In Ribbon with the degree of processing 50 and 65%, R phase rearrangement → R phase → B19' martensite transformation was occurred at 350℃. As the annealing temperature increased, the R → B19' transformation appeared, and the elongation increased and the ultimate tensile strength decreased.

(6) As the degree of processing increases, the diffraction peaks of martensite and austenite become broad and the intensity of the peaks decreases. But as the annealing temperature increases, the intensity of the diffraction peaks of the R phase (112) and (330) and the (110) plane of B2 is increased and the diffraction peak having the degree of processing of 65% is the largest. Also at an annealing temperature of 550℃ diffraction appeared on all sides.

(7) As-received wire showed the best shape recovery rate of 100% when they were not annealed. 35% was appeared 100% shape recovery rate at 250℃. And as the degree of processing increased, the shape recovery rate of 100% was appeared at 350℃. But as the annealing temperature was increased, the shape recovery rate decreased.