12 January, 2010
Lecture 1: Continuum aspects of plastic deformation in amorphous alloys
Abstract
Owing to vast differences in the structure and micro-mechanisms of plastic deformation of metallic glasses as compared to crystalline metals, completely new ways of understanding plasticity in these materials are required. In crystalline metals and alloys, whose plasticity is dislocation mediated, yield criteria are strictly deviatoric stress controlled with the hydrostatic state of stress having no role to play. In contrast, plastic flow in glasses is pressure sensitive, requiring yield criteria that incorporate these effects into the constitutive response. This lecture will focus on various yield criteria that are available for describing plastic flow in amorphous alloys, the consequences of pressure sensitivity on properties such as hardness and toughness.
References and suggested reading
- Schuh et al., “Mechanical Behavior of Amorphous Alloys,” Acta Materialia, vol 55, pp.4067-4109, 2007.
- Keryvin et al., “Temperature dependence of mechanical properties and pressure sensitivity in metallic glasses below glass transition,” Philosophical Magazine, vol. 88, pp.1773–1790, 2008.
Lecture 2 : Fracture and fatigue in amorphous alloys
Abstract
Metallic glasses are, at best, quasi-brittle materials, because they do not possess sufficient intrinsic micro-mechanisms to mitigate high stress concentrations at crack-tips. While some metallic glasses exhibit toughness values comparable to crystalline structural alloys; others are quite brittle, with characteristics similar to oxide or silicate glasses. The toughness of a metallic glass is also considerably more sensitive to structural variability or relaxation than is strength, which introduces an additional element of uncertainty in their reliable use. In this lecture, the fracture phenomenology, mechanisms and fatigue behavior of metallic glasses will be reviewed.
References and suggested reading
- Schuh et al., “Mechanical Behavior of Amorphous Alloys,” Acta Materialia, vol. 55, pp. 4067-4109, 2007.
- Xu et al., “On the Fracture Toughness of Bulk Metallic Glasses,” Journal of Metals, in press.