Transformation characteristics of TiNi/TiNi alloys synthesized by explosive welding

Abstract

Effects of severe deformation and heat treatment on the transformation behaviors of explosively welded duplex TiNi/TiNi shape memory alloys (SMAs) were investigated by the differential scanning calorimeter (DSC). The explosively welded duplex TiNi/TiNi plate of 0.7 mm in thickness was cold-rolled at room temperature to the extent of 60% reduction in thickness and then annealed at different temperatures (573-973 K) for different time (15 min-10 h). Low temperature (623-723 K) heat treatment led to amorphous crystallization. At higher temperature (873 K), the re-crystallization took place in the specimens. Analysis showed that the change of internal stresses is just the root cause of the change of transformation temperature. The relationships between the transformation behaviors and the heat treatment were discussed in the present report.

Functional properties of ‘Ti50Ni50–Ti49.3Ni50.7’ shape memory composite produced by explosion welding

“…Hence, the TiNi layers, with different Ni concentrations, underwent a B2 ↔ B19' transformation at different temperatures. This is in agreement with the data published in [8][9][10][11][12]. An estimation of the value of heat released and absorbed after cooling and heating as a square under the calorimetric peaks show that the value of the heat effect was smaller than the same value measured in annealed TiNi alloys.…”

“…To provide the necessary properties, the bimetal composite with an equiatomic TiNi alloy as a shape-memory alloy layer and a Ni-rich TiNi alloy as a pseudo-elastic layer was chosen. First, such composites were produced in [8][9][10][11][12], and Martensitic transformations were studied prior to and following annealing. It was found that the equiatomic TiNi and Ni-rich TiNi layers underwent Martensitic transformations at different temperatures; hence, we might choose a temperature at which the equiatomic TiNi layer was in a Martensite state and the Ni-rich TiNi layer was in an Austenite state.…”

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…Explosive welding for joining NiTi to itself was also studied by several authors [50][51][52][53][54][55]. In these studies, two different NiTi alloys, with different compositions and transformation temperatures, were used.…”

“…The objective was to obtain a NiTi/NiTi composite with macroscopic heterogeneities in chemical composition. In [50][51][52]54,55], after explosive welding of NiTi to itself a controlled thickness reduction was performed and the effect of heat treatments on the transformation temperatures to the welded joints was analysed. As expected, by a proper selection of the heat treatment temperature, the martensitic transformation could be adjusted so that the hysteresis of the transformation varied depending on the foreseen application.…”