INTERNAL-FRICTION AND YOUNG-MODULUS BEHAVIOR OF HOT-ROLLED CU-AL-NI-TI SHAPE-MEMORY ALLOYS

The internal friction (IF) and modulus behaviour during thermoelastic martensitic transformation in grain refined Cu-Al-Ni-Ti shape memory a lloys hot roiled at 650 degrees C and 850 degrees C has been studied u sing a three-point bending Dynamical Mechanical Analyser. in both allo ys, Ti-rich X-phase particles, mu m sized are formed and inhibit grain growth. Lower IF peaks and modulus minima have been observed in the s amples rolled at 650 degrees C, which is related to the presence of mi crometric gamma(2)-phase particles. During ageing at 250 degrees 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 tog ether 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.