Recovery Mechanisms in a Compressed Ni-Ti Superelastic Alloy

Abstract

The present work studied the influence of annealing on a Ni-Ti alloy submitted to uniaxial compression. The stress-strain curve under compression showed the absence of the Stress-InducedMartensite (SIM) plateau and 42% of remaining austenitic phase (B2). identified by the Electron Backscattered Diffraction (EBSD) technique on a Scanning Electronic Microscope (SEM). Annealing at 150 ºC increased the volume fraction of austenite to 70%. Annealing at 200 ºC reduced the volume fraction of austenite to 33% and increased the classical Vickers hardness and the dynamic elastoplastic hardness. This increase suggests the presence of a phase with higher indentation resistance, which can be the R phase reported in the literature. Annealing at 250 ºC decreased the classical Vickers hardness and the dynamic elastoplastic hardness, probably due to recovery. Annealing at 300 ºC advanced the recovery process and promoted some recrystallization, as suggested by the large standard deviation observed in the hardness results.

Mechanical behavior and fatigue life of micro welded joints obtained by TIG spots in NiTi wires

“…(1) hot mounting; (2) grinding using sandpapers of 280, 360, 400, 600, 1000 and 1200 grit; Vickers hardness (HV) measurements were carried out using a Shimadzu DUH-W211S Dynamic Ultra Micro Hardness Tester, with the following conditions of load/ unload [46]: maximum load 50 mN, permanence time on maximum load of 20 s, load/unload rate of 13.324 mN s −1 . All indentations were performed at room temperature and measurements were made from the center of the weld to the BM, because it was a symmetrical joint and the literature results indicated a good symmetry in the hardness profile of the joint [12,44].…”