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The stress-free thermal cycling with help of a differential scanning calorimeter
(DSC) is executed through the transformation range of a fully annealed Ni-Ti alloy sample,
continuously observing the variations in the calorimetric profiles and related thermal
parameters. The influence of two different cooling rates right after annealing on the
transformation properties is extra and separately examined. It is found that as the thermal
cycle number increases, the transformation sequence changes into a two-stage behaviour on
cooling, and the first visible symptoms related to the appearance of intermediate R-phase
occur after 10th full cycle. Apart from a progressive decrease of the critical temperatures, there
is no DSC evidence for the two-stage reaction on heating within the whole thermal cycling
test. As a result of the higher cooling rate after annealing, somewhat higher transformation
temperatures are measured for the Ni-Ti alloy.
Keywords: Ni-Ti SMA; stress-free thermal cycling; DSC analysis |
full paper (pdf, 1168 Kb)