Abnormal devitrification behavior and mechanical response of cold-rolled Mg-rich Mg-Cu-Gd metallic glasses. (1st September 2016)

• Record Type: Journal Article
• Authors: Lee, J.I.; Kim, J.W.; Oh, H.S.; Park, J.S.; Park, E.S.
• Is Part Of: Acta materialia. Volume 116(2016)
• Page Start: 238
• Page End: 249
• Publication Date: 2016-09-01
• Subjects: Metallic glass -- Cold rolling -- Structural instability -- Abnormal devitrification -- Mechanical response; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.06.026
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Abnormal devitrification behavior and mechanical response of Mg75 Cu15 Gd10 (relatively strong glass former with higher structural stability) and Mg85 Cu5 Gd10 (relatively fragile glass former with lower structural stability) metallic glasses, fabricated by repeated forced cold rolling, have been investigated. When metallic glasses were cold-rolled up to a thickness reduction ratio of ∼33%, the heat of relaxation (Δ H relax. ) below T g of the cold-rolled specimens was reduced, which indicates the formation of local structural ordering via cold rolling due to stress-induced relaxation. The local structural ordering results in abnormal devitrification behavior, such as higher resistance of glass-to-supercooled liquid transition and delayed growth, in the following heat treatment due to increased nuclei density and pinning site. In particular, the fragility index, m, could assist in understanding structural stability and local structural variation by mechanical processing as well as compositional tuning. Indeed, we examine the shear avalanche size to rationalize the variation of the deformation unit size depending on the structural instability before and after cold rolling. The deformation mode in Mg85 Cu5 Gd10 metallic glass might change from self-organized critical state to chaotic state by cold rolling, which results in unique hardening behavior under the condition for coexisting well distributed local structural ordering and numerous thinner shear deformed areas. These results would give us a guideline for atomic scale structural manipulation of metallic glasses, and help develop novel metallic glass matrix composites with optimal properties through effective mechanical processing as well as heat treatment. Graphical abstract: