Stress corrosion and corrosion fatigue of Zr-based bulk metallic glasses

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With this project new contributions to the fundamental understanding of the stress corrosion and corrosion fatigue behaviour of bulk-glass forming alloys will be made. The mechanical properties of selected Zr-based alloys will be analyzed in normal and corrosive conditions, i.e. under anodic dissolution, passivation-repassivation regimes and cathodic hydrogen charging. The bending behavior will be tested under quasi-static, static and cyclic loadings for determination of the ultimate bending strength, the fatigue life, the crack growth rate and the fracture toughness. Aim of the study is the clarification of the crack growth behavior in a basic manner. This requires an understanding of the interactions of alloy elements with ions from the surrounding medium acting on the crack development by modifying the crack tip morphology. Since cracks initiate and grow along shear bands, the interplay of shear bands with the corrosive medium must be clarified. To that end effects of glassy alloy composition yielding different reactivity, of nano-heterogeneities guiding the shear banding as well as of surface defects determining local topographic and mechanical stress states will be studied. Multi-scale in situ and ex situ microscopic and spectroscopic analysis of crack initiation and propagation will be conducted with special focus on crack tip regions.The goal is a better understanding of the governing processes in the structure during deformation. In metallic glasses the SRO/MRO state, i.e. the individual atom bindings and topologies are most important for the mechanical properties. Changes of these states through the corrosive environments will in turn change their reaction on static and cyclic load. Nano-heterogeneities in a glassy structure represent an additional structural factor affecting the mechano-corrosive degradation process. Principle mechanistic descriptions of stress corrosion and corrosion fatigue phenomena of metallic glasses will be developed and those will be discussed in relation to established mechanisms for silicate glasses and crystalline alloys. As main contribution to the overall goal of the SPP 1594 a topology-environment-mechanical properties (TEMP) relationship will be developed based on project results and supported by results of other SPP projects. From this work strategies for alloy modifications to inhibit stress-induced corrosion phenomena will be derived leading to ultra-strong metallic glasses with high environmental resistance.