Internal Friction and Young Modulus Behaviour of Hot-Rolled Cu-Al-Ni-Ti Shape Memory Alloys

Abstract

The internal friction (IF) and modulus behaviour during thermoelastic martensitic transformation in grain refined Cu-Al-Ni-Ti shape memory alloys hot rolled at 650°C and 850°C has been studied using a three-point bending Dynamical Mechanical Analyser. In both alloys, Ti-rich X-phase particles, μm sized, are formed and inhibit grain growth. Lower IF peaks and modulus minima have been observed in the samples rolled at 650°C, which is related to the presence of micrometric γ 2 -phase particles. During ageing at 250°C, a decomposition process in the form of a fine dispersion of precipitates with sizes of a few nm after 50-80 hours ageing has been observed, together with a progressive reduction in the IF peaks and modulus minima of the martensitic transformation. These reductionsare attributed to a loss of mobility of the parent/martensite interfaces in a oscillating stress cycle caused by the precipitates.