INTERNAL FRICTION MEASUREMENTS AND THERMODYNAMICAL ANALYSIS OF A MARTENSITIC TRANSFORMATION

Internal friction measurements as a function of temperature and strain amplitude have been performed on polycrystalline CuZnAl and Ti Ni alloys. These measurements show a typical "critical" behaviour round the temperature of the martensitic transformation : discontinuities in the internal friction curves, important decrease of some elastic constants and a thermal hysteresis between heating and cooling. In order to explain these results, theoretical calculations based on a Landau theory of first order phase transition have been performed. An important strain amplitude dependence is taken into account. It is assumed that the order parameter has the same dynamical behaviour as the one of the dislocations when they break away from pinning points. The thermal hysteresis is then explained without references to the influence of internal stresses