Influence of Primary Crystallization on Hydrogen Permeation in an Fe40Ni38Mo4B18 Amorphous Metallic Alloy

Samples of the amorphous metallic alloy Fe 40 Ni 38 Mo 4 B 18 were submitted to na isothermal crystallization treatment at a temperature of 858 K for different times. The kinetics of the crystallization process was measured using ferromagnetic resonance spectroscopy (FRM). The value of the Avrami exponent, n, for the Fe 40 Ni 38 Mo 4 B 18 alloy was found to be 1.10 ± 0.02 and the activation energy for crystallization obtained by differential scanning calorimetry, DSC, has a value of 302 ± 8 kJ.mol -1 . Amorphous and partially crystallized samples were submitted to electrochemical hydrogen permeation tests at 313 K. It was observed that, as the crystalline fraction increases, the apparent diffusivity, D app , decreases from 22 ± 0.4 x 10 -15 to 8.5 ± 0.3 x 10 -15 m 2 .s -1 . The apparent solubility also decreases, from 170 ± 6.0 molH m -3 to 38.3 ± 1.1 molH.m -3 . This suggests that the crystalline phase obtained by heat treatment of the Fe 40 Ni 38 Mo 4 B 18 alloy promotes a reduction in the mobility of the hydrogen atoms and in the number of sites for dissolution.