Isothermal effect on internal friction of Ti50Ni50 alloy measured by step cooling method in dynamic mechanical analyzer

The internal friction of TiNi-based SMAs measured by step cooling method in DMA may be misled when the used isothermal time interval t is insufficient. For Ti50Ni50 SMA, the tan δ values of B2 → R and R → B19′ internal friction peaks measured by step cooling method are lessening with prolonging the t value. This is because the tan δ value of IFTr still subsists and decreases continuously during the frequency sweep process. The t effect is more significant when the step cooling method is measured at lower frequency. According to the experimental results of Ti50Ni50 SMA, it is acceptable to choose t = 20 min to eliminate most of the influence of IFTr.