Crystallization of amorphous Ni 35Zr 65 and Fe 40Ni 40P 14B 6 under proton irradiation

Abstract

Two amorphous alloys, Ni 35Zr 65 and Fe 40Ni 40P 14B 6, were irradiated using 400 keV protons at several temperatures below the crystallization temperature, T x , to peak doses in the neighborhood of 3.5 to 4.5 dpa. Irradiation at 250°C resulted in the crystallization of both alloys, which were examined by transmission electron microscopy of samples electrolytically polished to various distances from the irradiated surface to study the effect of dose. Samples masked from the proton beam remained amorphous during irradiation. In the Ni 35Zr 65 alloy crystallization of the equilibrium phases propagated throughout the entire sample, while the in the Fe 40Ni 40P 14B 6 alloy crystallization was observed only in those parts of the samples lying within the proton range. Neither alloy crystallized during irradiation at 100°C. In both these alloys the amorphous phase is therefore evidently stable at irradiation temperatures below approximately 0.6 T x . An examination of the literature on irradiation damage of binary alloys and intermetallic compounds suggests that there is a tendency for initially amorphous alloys to remain amorphous at irradiation temperatures, T irr < 0.3 T L, where T L (≈ T x) is the “melting” temperature (either a eutectic, peritectic or congruent melting temperature). Also, these same alloys, even when they are initially crystalline, transform to the amorphous state during irradiation at T < 0.3 T L. Some other crystalline alloys have also been shown to transform to the amorphous state at T irr < 0.3 T L even though they have never been prepared in this condition by rapid quenching techniques. The temperature 0.3 T L appears to be a lower limit, however, since the crystalline to amorphous transformation occurs in many of these alloys at temperatures greater than 0.3 T L. It is suggested, by analogy with results on void formation in irradiated metals, that this low temperature limit is related to the low mobility of vacancies in these materials, although the mechanism of crystallization, or conversely amorphization, is not fully understood.