2-STAGE EMBRITTLEMENT OF AMORPHOUS FE40NI40P20 RESULTING FROM A LOSS OF FREE-VOLUME AND PHASE-SEPARATION

During thermal annealing, amorphous Fe//4//0Ni//4//0P//2//0 embrittles via a two-step process at 220 and 300 degree C. The first step results from a loss of excess free volume. This embrittlement is reversible; during subsequent neutron irradiation a swelling is observed which corresponds to an increase in excess volume and a restoration of ductility. Small angle neutron scattering reveals that the second step of embrittlement, during which the specimen remains fully amorphous, is induced by phase separation into regions enriched and depleted in P. Assuming a composition of (Fe, Ni)//7//5P//2//5, a volume fraction of only 5% of these P-rich clusters is sufficient to cause further embrittlement of the amorphous alloy.