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

该项目将对基本理解块状玻璃形成合金的应力腐蚀和腐蚀疲劳行为作出新的贡献。将分析选定的锆基合金在正常和腐蚀条件下的力学性能，即在阳极溶解、钝化-再钝化和阴极充氢条件下。将在准静态、静态和循环载荷下测试弯曲行为，以确定极限弯曲强度、疲劳寿命、裂纹扩展速率和断裂韧性。研究的目的是从根本上阐明裂纹的扩展行为。这需要了解合金元素与来自周围介质的离子之间的相互作用，通过改变裂纹尖端的形态来影响裂纹的发展。由于裂纹沿剪切带萌生和扩展，因此必须弄清剪切带与腐蚀介质之间的相互作用。为此，我们将研究产生不同反应活性的玻璃合金成分、引导剪切带的纳米异质性以及决定局部形貌和机械应力状态的表面缺陷的影响。将对裂纹的萌生和扩展进行多尺度的原位和非原位微观和光谱分析，重点是裂纹尖端区域。目的是更好地理解结构在变形过程中的控制过程。在金属玻璃中，SRO/MRO态，即单个原子的键合和拓扑对其力学性能是最重要的。这些状态通过腐蚀环境的变化，进而改变它们对静载荷和循环载荷的反应。玻璃结构中的纳米异质性是影响机械腐蚀降解过程的另一个结构因素。将对金属玻璃的应力腐蚀和腐蚀疲劳现象进行基本的机理描述，并将结合硅酸盐玻璃和晶态合金的已建立的机理进行讨论。作为对战略计划1594总体目标的主要贡献，将根据项目结果建立拓扑-环境-机械性能(TEMP)关系，并得到其他战略计划项目结果的支持。通过这项工作，将衍生出抑制应力诱导腐蚀现象的合金改性策略，从而获得具有高环境耐受性的超强金属玻璃。

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.