Recently, we have proposed a theory to analyze the first-order phase transition ͑FOPT͒ in solids. In order to test the concept of the physics of dissipation during FOPT in solids, it is necessary to test the theory with different FOPT system. We study here a burst-type martensite transformation in a Fe-18.8% Mn alloy sample for this purpose. We investigate the characteristics of ␥͑fcc͒ ͑hcp͒ transformation in this alloy and measure the dependence of internal friction ͑IF͒ during ␥/ transformation in varying rate of temperature Ṫ and vibration frequency. For free oscillations, the IF was defined to be Q ␦ Ϫ1 ϭ␦/ where ␦ is the logarithmic decrement. For general ͑forced͒ oscillations, IF is usually defined to be Q w Ϫ1 ϭ(1/2)(⌬W/W), where ⌬W is the dissipation over one cycle, while W is the maximum stored energy. During our analysis, the relation between Q ␦ Ϫ1 and Q w Ϫ1 is deduced. The parameter l ͑coupling factor between phase interface and oscillating stress͒ takes a small value ͑0.015-0.035͒ during PT, but takes a large value ͑0.86͒ during static state. The parameter n ͑exponent of rate for effective PT driving force͒ takes a large value 0.33 during heating and 0.47 during cooling. The physical meaning of n and l is discussed. The methodology introduced here appears to be an effective way of studying FOPT in solids. ͓S0163-1829͑96͒02533-7͔
In order to test the concept of the physics of dissipation during first-order phase transitions in solids, we measured the internal friction (Q Ϫ1) and the relative shear modulus () during a thermoelastic martensitic transformation in a NiTi alloy. We adopted two approaches: temperature variation and application of external stress. This investigation of internal friction was carried out with various vibration frequencies , temperature variation rates Ṫ , and strain variation rates. The index l ͑coupling factor between phase interface and oscillating stress͒ and index n ͑rate exponent for the effective phase transformation driving force͒ have been calculated from the experimental data for each case and the values of l and n are about the same in the two ͑doped͒ NiTi samples, irrespective of whether the phase transition is driven by a temperature variation or stress induced process. We compare the values of n and l for the NiTi samples with that of the other samples ͑VO 2 ceramics and FeMn alloys͒, reinforcing the previous physical interpretations of these indices. We believe the indices n and l are indeed fingerprints of first-order phase transitions in solids. ͓S0163-1829͑97͒00230-0͔
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