The effect of ageing on the damping properties of Cu–Al–Ni shape memory alloys

Abstract

Dynamic mechanical analysis (DMA) of β-phase aged single-crystal Cu-Al-Ni alloys was conducted to investigate the changes in the internal friction (IF) through the thermoelastic martensitic transformation temperature regime. Two alloys of different compositions, one in the martensitic and the other in the austenitic state at room temperature, were examined. Ageing of the alloys at three different temperatures, T a (473, 523 and 573 K), shows an increase in the transformation temperatures due to the successive martensitic transition (β 1 → γ 1 ) and γ 2 precipitate formation. Correspondingly, a progressive reduction in the IF peak in the transition regime with increase in the ageing temperature was observed in both the alloys. Formation of precipitates, which hinder the mobility of the martensite variant and parent/martensite interfaces, and an increase in their volume fraction with ageing are causes for the observed IF reduction.

Aging response and its effect on the functional properties of Cu–Al–Ni shape memory alloys

“…Moreover, the alloy M showed relatively higher tan δ values vis-à-vis the alloy A (Fig. 7 of [18]), for all the aging conditions [18]. In both the alloys A and M, the E value exhibited a trough at the phase transition regime, demonstrating the compliancy of the alloy during transformation.…”

“…3(a and b) in Ref. [18]), hence the focus here is only on the changes in properties while heating. Fig.…”

Mechanical resonance of the austenite/martensite interface and the pinning of the martensitic microstructures by dislocations inCu74.08Al23.13Be2.79<

“…24 It was reported there that the hardening was the same for samples which were aged to different degrees. In Cu 74.08 Al 23.13 Be 2.79 one could argue that the required strong pinning could be provided by decomposition of the sample 25 while TEM observations indicate that pinning happens via dislocations which nucleate during the martensitic phase transformation on dislocations inherited from the austenite.…”