Gradient Effects on Mechanical Properties of Metallic Glasses

Inhomogeneity exists in metallic glasses that naturally introduces variations of structural, chemical or property changes in different regions. The spatial variations lead to gradient of these quantities that in turn affects properties. In this presentation, I will examine in quantitative way how these gradients affect mechanical properties, in particular strength and toughness of metallic glasses. We show that in a sample with a continuously varying density, or density gradient, or free volume gradient, the internal stresses are affected through redistribution. This causes the local shear and later, shear band formation to be distributive. The larger the gradient, the more effective to prevent the local shear from concentrating in a single location, and thus, high toughness can be achieved. The principles we learned from these theoretical studies point to new use of gradient in design of metallic glasses and their composites. We show, in an example, that the thickness gradient of the regions with the network structure in a metallic glass composite can indeed help us to improve the toughness as well as strength. Lastly, we examine the length scales associated with the gradients and how they influence the mechanical behaviors of metallic glass and its composites.