Kinetics of martensitic transformations in some ferrous and non-ferrous alloys

The influence of hydrostatic pressure and magnetic fields on the athermal and the isothermal martensitic transformations in Fe-29.9 at. % Ni, Fe-31.7 at.% Ni, Fe-32.3 at.% Ni, Cu-29.1 at.% Al-3.6 at.% Ni and Fe-24.0 at.% Ni-4.0 at.% Mn alloys have been examined in order to clarify the difference between the athermal and isothermal transformation processes. The following results were obtained. Firstly, a martensitic transformation occurs after some incubation time during isothermal holding at a temperature higher than the transformation start temperature M-s in zero external field and no hydrostatic pressure for Fe-Ni and Cu-Al-Ni alloys which originally exhibit athermal martensitic transformations. Secondly, athermal martensitic transformations in Fe-Ni alloys change to isothermal transformations under hydrostatic pressure. Thirdly, in the isothermal martensitic transformation in an Fe-Ni-Mn alloy, a static magnetic field lowers the nose temperature and increases the incubation time required for the formation of martensite and a hydrostatic pressure raises the nose temperature and reduces the incubation time. These results suggest that the two transformation processes are closely related to each other as has been discussed on the basis of a phenomenological theory previously presented.