Abstract
In this investigation, the effect of various parameters of aging treatment on the superelastic behavior of Ni50.9Ti49.1 wires was studied. The samples were aged at 300, 350, 400, 450, 500, 550 and 600˚C for 10, 30 and 120 minutes. Tensile tests were performed for all samples. Results of the tensile tests for as-received sample show a low superelastic effect. It means that there are remained strains in as receive sample after loading and unloading cycle. The aging treatments with short and intermediate aging times result in increasing the superelastic property, while there are considerably remained strains in samples, aged at 450, 500, 550 and 600˚C for long aging time (120 minutes). Moreover the results indicate that, both upper and lower plateau stress are decreased with increasing the time and temperature of aging. The results of tensile experiments up to fracture for aged samples at different temperatures for 30 minutes show that with increasing the aging temperature up to 400˚C, the magnitude of fracture stress increases slowly. With increasing the aging temperature more than 400˚C, the fracture stress decreases. As the aging temperature increase, the strain content of plateau increase. Therefore, we can conclude that combined use of work-hardening and age-hardening is more effective to increase the critical stress for slip and consequently to improve superelasticity
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