Accommodation Stresses and Structural-Phase Transitions in Fe-Ni Alloys upon Compression in Bridgman Anvils

Mossbauer spectroscopy was used to study polymorphic phase transitions in iron and Fe-Ni (15, 25, 32 at % Ni) alloys in situ in Bridgman anvils under a quasi-hydrostatic compression to 25 GPa. A connection has been established between the type of polymorphism and degree of transformations on the one hand and the hyperfine parameters, magnetic texture, and stresses in the structure of the initial and resultant phases on the other hand. In iron and in the Fe-15 % Ni alloy, a baroelastic change in the direction of the magnetic texture of the a phase has been revealed, which is caused by the appearance of oriented accommodation stresses between the a and e phases. In the range of compositions of 15-25 at % Ni, the appearance of a hyperfine magnetic structure of spectra of the high-pressure phase has been found.