ANALYSIS OF DISSIPATION OF A BURST-TYPE MARTENSITE-TRANSFORMATION IN A FE-MN ALLOY BY INTERNAL-FRICTION MEASUREMENTS

Recently, we have proposed a theory to analyze the first-order phase t ransition (FOPT) in solids. In order to test the concept of the physic s of dissipation during FOPT in solids, it is necessary to test the th eory with different FOPT system. We study here a burst-type martensite transformation in a Fe-18.8% Mn alloy sample for this purpose, We inv estigate the characteristics of gamma(fcc)reversible arrow epsilon(hcp ) transformation in this alloy and measure the dependence of internal friction (LF) during gamma/epsilon transformation in varying rate of t emperature T and vibration frequency omega. For free oscillations, the IF was defined to be Q(delta)(d-1) = delta/pi where delta is the loga rithmic decrement. For general (forced) oscillations, IF is usually de fined to be Q(w)(-1) = (1/2 pi)(Delta W/W), where Delta W is the dissi pation over one cycle, while W is the maximum stored energy. During ou r analysis, the relation between Q(delta)(-1), and Q(W)(-1) is deduced . The parameter I (coupling factor between phase interface and oscilla ting stress) takes a small value (0.015-0.035) during PT, but takes a large value (0.86) during static state. The parameter n (exponent of r ate for effective PT driving force) takes a large value 0.33 during he ating and 0.47 during cooling. The physical meaning of n and I is disc ussed. The methodology introduced here appears to be an effective way of studying FOPT in solids.