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 γ₂ 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.