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In this paper, the plastic deformation behavior and strain homogeneity of the ZK60 Mg alloy during the multi-pass cyclic extrusion and compression (CEC) was simulated using the finite-element method (FEM) with a view to provide an insight into the mechanics of the process. Physical modeling (PM) experiment with same alloy was carried out to verify the results of the numerical simulations. The results show that two vortex flow regions with opposite flow direction are formed inside the cylindrical workpiece during CEC deformation. Although the deformation is inhomogeneous in both end regions of workpiece, a uniform region of equivalent strain exists, and the extent of uniform deformation increased with the increase in workpiece length. [ABSTRACT FROM AUTHOR]

The design of ductile heterogeneous metallic glasses (MGs) with enhanced deformability by purposely controlling the shear-band dynamics via modulation of the atomic-scale structures and local stress states remains a significant challenge. Here, we correlate the changes in the local atomic structure when cooling to cryogenic temperature with the observed improved shear stability. The enhanced atomic-level structural and elastic heterogeneities related to the nonaffine thermal contraction of the short-range order (SRO) and medium-range order (MRO) change the characteristics of the activation process of the shear transformation zones (STZs). The experimental observations corroborated by Eshelby inclusion analysis and molecular dynamics simulations disclose the correlation between the structural fluctuations and the change in the stress field around the STZ. The variations in the inclination axes of the STZs alter their percolation mechanism, affect the shear-band dynamics and kinetics, and consequently delay shear failure. These results expand the understanding of the correlation between the atomic-level structure and elementary plastic events in monolithic MGs and thereby pave the way for the design of new ductile metallic alloys. Metallic glasses: seeing the effects of stress Recent insights into the atomic-scale mechanisms underlying the structural failure of glass-like metals provide strategies for the development of novel materials. Metallic glasses have a disordered atomic structure, unlike the crystalline arrangement of conventional metals. They therefore offer greater flexibility in terms of the shapes they can form. However, so-called shear bands that form when the metallic glass is deformed under stress weaken it, leading to structural failure. G.W. from Shanghai University, China, D.Ş. from the Erich Schmid Institute of Materials Science in Leoben, Austria, and co-workers used X-ray diffraction to track changes in atomic structure as they cooled a metallic glass to very low temperatures and correlated these changes with local variations in stress. Understanding this correlation will help design metallic glasses with an improved ability to be deformed without structural failure. Understanding the correlation between atomic-scale structural/elastic fluctuations and local plastic rearrangements (shear transformation zone (STZ)) is essential to the widespread use of metallic glasses (MGs). We report a strategy to control the local stress state and enhance the shear stability of MGs. The enhanced degree of structural/elastic heterogeneities relates to the increased nonaffine thermal strain of the short- and medium-range order. We demonstrate that variations in the stress field around STZ affect their dynamics and percolation process, the progressive formation of shear bands, and, consequently, the macroscopic deformability of MGs. This work paves a new way for designing ductile MGs. [ABSTRACT FROM AUTHOR]

Examines the dynamic tensile behavior of the Zr[sub 41.2]Ti[sub 13.8]Cu[sub 12.5]Ni[sub 10]Be[sub 22.5] bulk metallic glass. Preparation of the alloy ingots by arc melting pure metals in a purified argon atmosphere; X-ray diffraction pattern of the cast cylindrical Zr[sub 41.2]Ti[sub 13.8]Cu[sub 12.5]Ni[sub 10]Be[sub 22.5] rod; Dynamic fracture surface and dynamic tensile stress-strain curves of the bulk metallic glass; Evidence that the tensile strength and the fracture morphology of the alloy strongly depend on the strain rate.

Reports on observations pertaining to the strain rate dependence of cyclic stress response and evolving deformation substructure of K40S cobalt-base superalloy at 900 degrees Centigrade. Typical microstructure of K40S alloy; Explanation of the cyclic stress response behavior; Interfacial dislocations resulting from a stress due to secondary carbide M23C6 volume change.