Simulation of the growth of inert gas bubbles near the surface of an amorphous alloy

Abstract

Using an interatomic potential technique, an overpressurized gas bubble in an amorphous metal was simulated for various pressures. Above an excess pressure P exc of nearly 75 kbar, the material around the bubble undergoes a continuous irreversible deformation, as found in experiments. On the basis of this value of P exc, a good description can be given of several experimental facts concerning gas bubble growth in amorphous alloys (e.g. the dimension of the bubbles as a function of dose). This P exc value is considerably higher than bubble pressures usually observed in crystalline material, which reveals a different growth mechanism for bubbles. Instead of loop punching as observed in crystals, local rearrangements of small groups of atoms are a more probable mechanism. The excess gas pressure found in the simulation approximates ( 1 2π ) times the material shear modulus, which is approximately the theoretical strength of a crystalline material. The value of P exc is confirmed by a recent measurement using EELS techniques. The high P exc permits in principle the crystallization of some noble gases in the precipitates at room temperature.