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MM: Fachverband Metall- und Materialphysik

MM 22: Mechanical properties I - Plastic deformation & fracture

MM 22.1: Vortrag

Dienstag, 1. April 2014, 10:15–10:30, IFW B

Ductile-to-brittle transition in metallic glasses under cryogenic cooling — •Minqiang Jiang — State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, PR China — Institute of Materials Physics, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany

At temperatures well below the glass transition temperature, the failure of metallic glasses is generally induced by shear-banding that is a result of the self-organized shear transformation zones (STZs). Here, we demonstrate that upon cooling down to liquid-helium temperature (4.2 K), a Zr-based metallic glass can fail via cavitation rather than by shear-banding due to the intervention of a ductile-to-brittle transition. This is supported by the breakdown of low-temperature strengthening of materials, as well as the change of fracture modes from shear to tension and fracture morphologies from vein-pattern to fine dimple or nanoscale periodic corrugation. We propose that a temperature-dependent STZ-dilatation, defined as the ratio of mobile free-volume to STZ-volume, controls the ductile-to-brittle transition, and across the transition point the STZ-type rearrangements of atomic-cluster will convert into the cavitation-dominated operations, i.e., tension transformation zones. Our findings shed new insight into fracture strength and energy dissipation mechanism in amorphous alloys, particularly at very low temperatures.