AMORPHIZATION KINETICS OF ZR3FE UNDER ELECTRON-IRRADIATION

Previous investigations using Ar-40-ion bombardments have revealed tha t Zr3Fe, which has an orthorhombic crystal structure, undergoes an irr adiation-induced transformation from the crystalline to the amorphous state. In the present investigation, 0.9 MeV electron irradiations wer e performed at 28-220 K in a high-voltage electron microscope (HVEM). By measuring the onset, spread and final size of the amorphous region, factoring in the Gaussian distribution of the beam, a kinetic descrip tion of the amorphization in terms of dose, dose rate and temperature was obtained. The critical temperature for amorphization by electron i rradiation was found to be approximately 220 K, compared with 570-625 K for Ar-40-ion irradiation. Also, the dose-to-amorphization increased exponentially with temperature. Results indicated that the rate of gr owth of the amorphous region under the electron beam decreased with in creasing temperature and the dose-to-amorphization decreased with incr easing dose rate. The size of the amorphous region saturated after a g iven dose, the final size decreasing with increasing temperature, and it is argued that this is related to the existence of a critical dose rate, which increases with temperature, and below which no amorphizati on occurrs.