The Effect of Thermal Cycling on B2→B19→B19′ Transformations of Ti₅₀Ni₄₀Cu₁₀ Shape Memory Alloy by Dynamic Mechanical Analyzer

Abstract

The effect of thermal cycling on B2→B19→B19′ transformations of cold-rolled and annealed Ti₅₀Ni₄₀Cu₁₀ SMA was examined by DMA. Experimental results point out the transformation peak temperature and its tanδ peak value of B19→B19′ transformation are more suppressed by thermal cycling than those of B2→B19. This is because of the different microstructures between B19 and B19′ martensites in which B19 is a defect-free martensite but B19′ has plenty of twinning. Dislocations induced by thermal cycling can hinder the mobility of twin boundaries of B19′ martensite and cause different thermal cycling effects on B2→B19 and B19→B19′ transformations. Thermal cycling also shows an obvious effect on storage modulus E₀ values of B19 and B19′ martensites and their E₀ values increase with increasing thermal cycles.