Mossbauer spectroscopy study of the crystallisation behaviour of Fe-Ni-Si-P amorphous powders prepared by ball milling

Crystallisation of ball milled amorphous powders with the overall composition Fe40Ni40P20-xSix (x=6, 10, 14) are studied by X-ray diffraction and transmission Mossbauer spectroscopy. Structural relaxation and growth of preexisting phases appear at temperatures below 473K. Further annealing at higher temperature results in the complete crystallization of the material. Different amorphisation ability of the resulting amorphous powders is determined as a function of the Si/P content. The crystallisation products determined - Fe(Si) bcc and Fe-Ni fee phases, Ni rich silicides and Fe-Ni phosphides- are the same as those obtained after crystallization of melt spun amorphous alloys of the same composition. The collapse of the magnetic hyperfine field, characteristic of INVAR Fe-Ni fee phases with compositions in the 30-40at% Ni range, is observed. However, this magnetic collapse is not obtained in the corresponding amorphous alloys obtained by melt spinning which, on the contrary, show the precipitation of both ferromagnetic and paramagnetic Fe-Ni fee phases. Although this behaviour seems to indicate the precipitation of Fe-richer phases, the mechanical stresses introduced in the material are also known to be able to induce such different magnetic behaviour.