Chemical boundary engineering expands the dimensionality of alloy design.

The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material’s microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material’s strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing.

A biodegradable and self-electrified conduit device is achieved to offer postoperative electrical cues for nerve regeneration.

Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences from those of established steel grades, especially pertaining to the microstructural variety that can be tuned and the associated micromechanisms activated during deformation. The interplay and tuning opportunities between composition and the many microstructural features allow to trigger almost all known strengthening and strain-hardening mechanisms, enabling excellent strength-ductility synergy, at relatively lean alloy content. Previous investigations have revealed a high degree of microstructure and deformation complexity in such steels, but the underlying mechanisms are not adequately discussed and acknowledged. This encourages us to critically review and discuss these materials, focusing on the progress in fundamental research, with the aim to obtain better understanding and enable further progress in this field. The review addresses the main phase transformation phenomena in these steels and their mechanical behaviour, covering the whole inelastic deformation regime including yielding, strain hardening, plastic instability and damage. Based on these insights, the relationships between processing, microstructure and mechanical properties are critically assessed and rationalized. Open questions and challenges with respect to both, fundamental studies and industrial production are also identified and discussed to guide future research efforts.