Damping Capacities of Ti₅₀Ni_50&minus;<i>_x</i>Cu<i>_x</i> Shape Memory Alloys Measured under Temperature, Strain, and Frequency Sweeps

Abstract

The damping capacities of Ti 50 Ni 50¹x Cu x SMAs with x = 0³20 at% were measured by DMA under temperature, strain and frequency sweep tests. The tan ¤ value exhibited at B2¼B19 transformation is significantly higher than that at B2¼B19A transformation under temperature/strain sweep tests. In the strain sweep test, the tan ¤ value decreases as the frequency increases, but it increases as the applied strain increases. The tan ¤ curves of the strain sweep tests can be fitted by tan ¤ = K¾ n with n values being close to the friction type model. Adding Cu enhances the tan ¤ values of both B19 martensite and B2¼B19 transformation in 0.1³10 Hz, but that of B19A martensite is enhanced only at 10 Hz. From 0.1 Hz to 1 Hz, the decrement of the tan ¤ value in IF I term is greater than that in IF PT term for SMA with x ² 5 at%. In the frequency sweep test, the tan ¤ value increases as the x value increases under the same applied frequency, no matter whether the martensite is B19A or B19.

Damping Characteristics of Ti50Ni50−xCux (x = 0~30 at.%) Shape Memory Alloys at a Low Frequency

“…Although the tan δ values in this study are most contributed from the transitory term (IF Tr ), as mentioned in Section 2.1, but from the strain sweep tests [17], we found that the phase transformation term (IF PT ) and the intrinsic term (IF I ) associated with B2↔B19 transformation are also higher than those associated with B2↔B19’ transformation. The magnitude of the tan δ value exhibited by IF PT term and that by IF I term are closely related to the mobility of the phase interface between the parent phase and martensite and the twin boundary between the martensite variants.…”

“…Here, M S ’and M S are the starting transformation temperatures of B2→B19 and B19→B19’, respectively. The DSC curves for x = 7.5 at.% SMA also show only a B2↔B19’ peak in cooling and heating [17]. Obviously, the DMA curves for x = 7.5 at.% SMA, as shown in Figure 1c, cannot be used to distinguish the B19 martensite from B2↔B19’ transformation, as revealed in ρ and DSC tests.…”