Plastic Deformation Of Metallic Glasses Research Articles

Microscopic Mechanism of Plastic Deformation in Metallic Glasses

Microscopic Mechanism of Plastic Deformation in Metallic Glasses

Diffusion in metallic glasses

Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated. It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.

Plastic deformation in metallic glasses

A theory is presented for the plastic deformation of metallic glasses below their glass transition temperature. The theory is based on two modes of thermally activated shear transformations initiated around free volume regions under an applied shear stress. The regions are typically conceived to be about 5 atom diameters across. At high temperatures (0.6 T g ≲ T ≲ T g ) the transformation is a diffuse rearrangement producing a relatively small local shear strain in a roughly spherical region. At low temperatures (0 < T ≲ 0.6 T g ) the transformation is in a narrow disk shaped region and resembles closely the nucleation of a dislocation loop. The theory is in good accord with experimental observations. Based on the theory, possible levels of flow dilatation have been computed from which rates of shear localization can be obtained. At low temperatures, very rapid shear localization is predicted which is in good accord with the observations reported in the literature and with recent cinematographic observations.