Determination of heat of transformation in a cold-rolled martensitic tini alloy |
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Authors: | H C Lin S K Wu |
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Affiliation: | (1) Department of Materials Science, Feng Chia University, Taichung, Taiwan, Republic of China;(2) Institute of Materials Science and Engineering, National Taiwan University, 106 Taipei, Taiwan, Republic of China |
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Abstract: | We studied the heat of transformation, ΔH, in martensitic transformations in a cold-rolled equiatomic TiNi alloy with differential
scanning calorimetry (DSC), X-ray diffraction (XRD), and microhardness measurements. Results of our experiment indicate that
the martensite stabilization and stress-induced parent (SIP)B2 phase are introduced when the TiNi martensite is cold rolled at room temperature. The SIP formation seems to be related to
the lattice softening phenomenon occurring in the martensite, while the ΔH value of the first reverse martensitic transformation
decreases enormously for the cold-rolled equiatomic TiNi alloy. We are proposing possible explanations for these results:
(1) the occurrence of SIP, which reduces the transformable martensite volume; (2) the release of accumulated elastic energy
induced by the cold rolling; and (3) the recovery of defects induced by cold rolling and release of the heat of recovery.
We also found that the retained dislocations can depress the martensitic transformation temperatures and induce the R-phase
transformation after the occurrence of the first reverse martensitic transformation.
Formerly Graduate Student, Institute of Materials Science and Engineering, National Taiwan University |
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