Work toughening effect in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

Abstract

Work hardening is a well-known phenomenon occurring in crystalline metals during deformation, which has been widely used to increase the strength of metals although their ductility is usually reduced simultaneously. Here we report that the plastic strain of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (at.%) bulk metallic glasses has been increased from 0.3% for the as-cast sample to 2.5%-8.0% for samples that have experienced pre-deformation under constrained conditions. The pre-deformed glassy alloys possess more free volume and abundant introduced shear bands, which are believed to promote the activation of shear bands in post-deformation and result in an increase in plasticity. The orientation of the pre-introduced shear bands relative to the loading direction will affect the deformation behavior of pre-deformed samples. The present results show that pre-deformation of this glassy alloy will result in work toughening. This work toughening effect can be removed by isothermal annealing at a sub-T g (glass transition) temperature, which causes annihilation of free volume and healing of shear bands. It is well known that most bulk metallic glasses (BMGs) possess super-high strength but very low global plasticity. The accepted reason for the limited plasticity of BMGs is that BMGs possess a tendency to form highly-localized shear bands which result in early fracture of the materials. It is obvious that deformation behavior of BMGs is quite different from crystalline metals, in which plastic deformation corresponds to the generation and motion of large numbers of dislocations. As the dislocation density increases with the plastic deformation, the interactions among dislocations are also increased, resulting in an increase in the resistance to dislocation movement. Then, further deformation requires an increase in the applied stress. This is the so-called "strain hardening" or "work hardening". However, since there are no dislocations in glassy alloys, absolutely no strain hardening resulting from interactions among dislocations can be observed in BMGs. So it is very difficult for glassy alloys to deform uniformly. Instead, highly localized shear bands [1] form easily during the deformation process, resulting in limited global plasticity of BMG. So to enhance the plasticity of BMGs, it is necessary to promote the activation of multiple shear bands [2-10] and hinder the localization and rapid propagation of shear bands [11][12][13][14][15][16][17][18][19]. Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7]. Because the partially relieved local heating and hindrance of the propagation of shear bands, both the strength and the ductility of a Zr-bas...

Review on the Research and Development of Ti-Based Bulk Metallic Glasses

“…For conventional crystalline alloys, after plastic deformation, the microstructure can be changed (e.g., dislocation density), and the flow behaviors can be quite different. For BMGs, pre-plastic deformation is supposed to introduce microstructural inhomogeneities and induce controlled stress distributions or activate multiple shear bands, which are beneficial to enhancing the room temperature plasticity [183,184]. Huang et al utilized prior compressive plastic deformation to tune the room temperature plasticity of Ti 40 Zr 25 Ni 3 Cu 12 Be 20 BMG [185].…”

Nanometallic Glasses: Size Reduction Brings Ductility, Surface State Drives Its Extent

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Amorphous alloys — A kind of promising high-performance materials

“…The result is a delightful one. We have 17 papers collected in this special issue, which cover broad areas of amorphous alloys, including atomic packing and clusters formation in amorphous alloys [1-3], fragility in glass-forming liquid [4], effects of alloying elements on the glass forming ability of different alloys [5][6][7], deformation behavior and improved mechanical property of amorphous alloys [8][9][10][11], glass-based composites [12,13], high strength metallic glass [14] and functional properties of metallic glasses [15][16][17].…”