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Abstract Compositional complex alloys, including high and medium‐entropy alloys (HEAs/MEAs) have displayed significant potential as efficient electrocatalysts for the oxygen evolution reaction (OER), but their structure‐activity relationship remains unclear. In particular, the basic question of which crystal facets are more active, especially considering the surface reconstructions, has yet to be answered. This study demonstrates that the lowest index {100} facets of FeCoNiCr MEAs exhibit the highest activity. The underlying mechanism associated with the {100} facet's low in‐plane density, making it easier to surface reconstruction and form amorphous structures containing the true active species is uncovered. These results are validated by experiments on single crystals and polycrystal MEAs, as well as DFT calculations. The discoveries contribute to a fundamental comprehension of MEAs in electrocatalysis and offer physics‐based strategies for developing electrocatalysts.

High-entropy alloys (HEAs) have emerged as a promising platform for designing efficient electrocatalysts; however, the relationship between their structure and activity has not yet been clearly established. In particular, the influences of crystalline defects, such as grain boundaries (GBs), on activity and stability remain unclear. This study demonstrates the impacts of GBs on the oxygen evolution reaction (OER) activity in the FeCoCrNi HEA. We observe a logarithmic dependence of OER performance on mean grain size, spanning 3 orders of magnitude, as measured by evaluators like overpotential and Tafel slope. Spatially resolved microscopic imaging of activated samples indicates that the GBs undergo substantial reconstructions and they are enriched with the in situ formed metal oxides (M-O, M = Fe, Co, Ni) and the amorphous regions. By comparing with simple metals, we reveal a “high-entropy effect,” i.e., HEAs exhibit greater tolerance towards the grain refinements, which explains their activity both in bulk samples and nanoparticles. These findings offer physics-informed strategies for developing HEA electrocatalysis.

Microstructure, mechanical properties and phase transformation of a heat-resistant rare-earth (RE) Mg-16.1Gd-3.5Nd-0.38Zn-0.26Zr-0.15Y (wt.%) alloy were investigated. The as-cast alloy is composed of equiaxed α-Mg matrix, net-shaped Mg5RE and Zr-rich phases. According to aging hardening curves and tensile properties variation, the optimized condition of solution treatment at 520 °C for 8 h and subsequent aging at 204 °C for 12 h was selected. The continuous secondary Mg5RE phase predominantly formed at grain boundaries during solidification transforms to residual discontinuous β-Mg5RE phase and fine cuboid REH2 particles after heat treatment. The annealed alloy exhibits good comprehensive tensile property at 350 °C, with ultimate tensile strength of 153 MPa and elongation to fracture of 6.9%. Segregation of RE elements and eventually RE-rich precipitation at grain boundaries are responsible for the high strength at elevated temperature. [ABSTRACT FROM AUTHOR]

To overcome the disadvantages of inhomogeneous microstructures and poor mechanical properties of additively manufactured Ti-6Al-4V alloys, a novel technique of hybrid deposition and synchronous micro-rolling is proposed. The micro-rolling leads to equiaxed prior β grains, thin discontinuous intergranular a, and equiaxed primary α, in contrast to the coarse columnar prior β grains without the application of micro-rolling. The recrystallization by micro-rolling results in discontinuous intergranular α via the mechanism of strain and interface-induced grain boundary migration. The evolution of α globularization, driven by a solute concentration gradient, starts from the sub-boundary until the formation of equiaxed primary α. Simultaneous strengthening and toughening are achieved, which means an increase in yield strength, ultimate tensile strength, fracture elongation, and work hardening rate. The formation of α recrystallization leads to more fine grain boundaries to strengthen the yield strength, and the improvement of ductility is due to the better-coordinated deformation ability of discontinuous intergranular α and equiaxed primary α. As a result, the fracture mode in micro-rolling changes from intergranular type to transgranular type. [ABSTRACT FROM AUTHOR]