THERMALLY INDUCED EMBRITTLEMENT OF Fe-Si-B-Cu-Nb AMORPHOUS ALLOYS
The effect of isochronal annealing on structure and mechanical properties of amorphous Finemet-type Fe73Si15.8B7.2Cu1Nb3 and Fe73.6Si15.8B7.2Cu1Nb2.4 alloys was studied by X-ray diffraction, microhardness measurements and bend testing. It was established that annealing at temperatures in the range 260-270°C resulted in the essential loss of ductility caused by the relaxation processes. On the base of analysis of the experimental results and the literature data it has been proposed that the most probable reason of embrittlement of the investigated alloys is irreversible relaxation of the quenched-in stresses due to ascending diffusion of metalloid atoms into surface layers of ribbons thus lowering their ductility.