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The effects of hydrogen in metals are a pressing issue causing severe economic losses due to material deterioration by hydrogen embrittlement. A crucial understanding of the interactions of hydrogen with different microstructure features can be reached by nanoindentation due to the small volumes probed. Even more, in situ testing while charging the sample with hydrogen prevents the formation of concentration gradients due to hydrogen desorption. Two custom electrochemical cells for in situ testing were built in-house to charge the sample with hydrogen during nanoindentation: “front-side” charging with the sample and the indenter tip immersed into the electrolyte, and “back-side” charging where the analyzed region is never in contact with the solution. During front-side charging, surface degradation often occurs which also negatively influences analyses after hydrogen charging. The back-side charging approach proposed in this work is a promising technique for studying in situ the effects of hydrogen in alloys under mechanical loads, while completely excluding the influence of the electrolyte on the nanoindented surface. Hydrogen diffusion from the charged back-side toward the testing surface is here demonstrated by Kelvin probe measurements in ferritic FeCr alloys, used as a case study due to the high mobility of hydrogen in the bcc lattice. During nanoindentation, a reduction on the shear stress necessary for dislocations nucleation due to hydrogen was observed using both setups; however, the quantitative data differs and a contradictory behavior was found in hardness measurements. Finally, some guidelines for the use of both approaches and a summary of their advantages and disadvantages are presented. Graphical abstract

To alleviate the mechanical instability of major shear bands in metallic glasses at room temperature, topologically heterogeneous structures were introduced to encourage the multiplication of mild shear bands. Different from the former attention on topological structures, here we present a compositional design approach to build nanoscale chemical heterogeneity to enhance homogeneous plastic flow upon both compression and tension. The idea is realized in a Ti-Zr-Nb-Si-XX/Mg-Zn-Ca-YY hierarchically nanodomained amorphous alloy, where XX and YY denote other elements. The alloy shows ~2% elastic strain and undergoes highly homogeneous plastic flow of ~40% strain (with strain hardening) in compression, surpassing those of mono- and hetero-structured metallic glasses. Furthermore, dynamic atomic intermixing occurs between the nanodomains during plastic flow, preventing possible interface failure. Our design of chemically distinct nanodomains and the dynamic atomic intermixing at the interface opens up an avenue for the development of amorphous materials with ultrahigh strength and large plasticity.