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High-entropy alloys (HEAs) display outstanding mechanical properties which make possible new technological applications. There are many studies of bulk HEAs, but here we focus on FeCrNiCuCo single-crystal face-centered cubic (FCC) samples with 40% and 50% nanoscale porosity, where the pores constrain plasticity. In order to disentangle the role of chemical complexity during deformation, we compare HEA samples to Average Atom (AA) samples with the same average properties as the HEA, but where all atoms are equivalent. Elastic modulus and plastic yielding are much higher than expected from Au nanofoam scaling predictions. We find that HEA and AA materials behave similarly to each other and to other FCC nanoporous samples until the point where failure begins. Deformation produces mostly partial dislocations that move and leave behind stacking faults crossing filaments, with sessile dislocations and some dislocation tangles forming due to the large plastic strain. Differences in sample failure modify the evolution of void and ligament size distributions. The AA sample presents ductile necking and ductile fracture of a few filaments, as in other single element FCC nanoporous samples. Failure in the HEA sample not only includes some ductile filaments fracture, but also brittle fracture of the filaments due to localized shear, which causes plane slippage, as identified by machine learning methods. Therefore, chemical complexity diminishes ductility in nanoporous FCC HEA samples. [ABSTRACT FROM AUTHOR]

Strong and ductile materials that have high resistance to corrosion and hydrogen embrittlement are rare and yet essential for realizing safety-critical energy infrastructures, hydrogen-based industries, and transportation solutions. Here we report how we reconcile these constraints in the form of a strong and ductile CoNiV medium-entropy alloy with face-centered cubic structure. It shows high resistance to hydrogen embrittlement at ambient temperature at a strain rate of 10−4 s−1, due to its low hydrogen diffusivity and the deformation twinning that impedes crack propagation. Moreover, a dense oxide film formed on the alloy's surface reduces the hydrogen uptake rate, and provides high corrosion resistance in dilute sulfuric acid with a corrosion current density below 7 μA cm−2. The combination of load carrying capacity and resistance to harsh environmental conditions may qualify this multi-component alloy as a potential candidate material for sustainable and safe infrastructures and devices. Strong and ductile materials with resistance to both corrosion and hydrogen embrittlement remain rare and yet are essential for hydrogen-propelled industries. Here, the authors show that a CoNiV medium-entropy alloy with face-centered cubic structure fulfils all the above criteria. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) are potential candidate materials for use in next-generation nuclear reactors due to their excellent mechanical performance at high temperatures. Here, we investigate the microstructure and mechanical properties of the nanocrystalline RHEA TiZrNbHfTa before and after irradiation with He2+ ions to determine radiation-induced property changes. Using nanoindentation and in situ microtensile testing we find only small changes in hardness after irradiation but a significant increase in yield and ultimate tensile strength without loss in ductility. This is associated with radiation hardening and a shift from shear localization failure with smooth fracture surfaces to a fracture morphology consisting of fine dimples and intergranular failure characteristics. Overall, the material shows excellent damage-tolerant properties with good combinations of strength and ductility both prior to and after ion irradiation. [ABSTRACT FROM AUTHOR]

The microstructure and thermal and mechanical properties of (FeCoNiCuCr)100−x-Nbx multiprincipal-element alloys have been investigated in the as-cast and heat-treated state. The alloys were smelted by arc-melting in argon atmosphere. As-cast samples were produced by copper mold casting. The structure was studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The calculated phase diagrams of the Fe-Co-Ni-Cu-Cr-Nb system were used to predict the phase composition. The predicted thermodynamic temperatures and phase areas were compared with those obtained using differential scanning calorimetry (DSC) and the results of SEM observation, respectively. Addition of 10 at.% Nb caused phase separation of the alloy in the liquid state. Addition of Nb caused an increase in the yield strength by solid-solution hardening and by the formation of intermetallic compounds. Heat treatment also affected the mechanical properties of the studied alloys. [ABSTRACT FROM AUTHOR]

Mechanical failure of polycrystalline metals is often difficult to predict, in part because of the wide range of conditions under which individual elements of the material's microstructure fail. We describe an efficient method for posing, assessing, and optimizing failure criteria for individual microstructural elements, such as grains, grain boundaries, precipitates, or precipitate-matrix interfaces. Such criteria may lead to improved failure predictions for polycrystalline metals. Our method constructs a failure probability function from a database of individual failure events obtained from experiments on polycrystalline samples. It then uses the Kullback-Leibler (K-L) divergence to compare it to probability densities corresponding to specific hypothesized failure mechanisms. The likeliest failure mechanism is the one that minimizes the K-L divergence with respect to a suitably chosen null hypothesis. As a demonstration, we apply this approach to hydrogen-assisted crack initiation at coherent twin boundaries in Ni-based alloy 725 and deduce a best-fit failure criterion for them. [ABSTRACT FROM AUTHOR]

Twin boundaries (TBs) in Ni-based superalloys are vulnerable sites for failure in demanding environments, and a current lack of mechanistic understanding hampers the reliable lifetime prediction and performance optimisation of these alloys. Here we report the discovery of an unexpected γ″ precipitation mechanism at TBs that takes the responsibility for alloy failure in demanding environments. Using multiscale microstructural and mechanical characterisations (from millimetre down to atomic level) and DFT calculations, we demonstrate that abnormal γ″ precipitation along TBs accounts for the premature dislocation activities and pronounced strain localisation associated with TBs during mechanical loading, which serves as a precursor for crack initiation. We clarify the physical origin of the TBs-related cracking at the atomic level of γ″-strengthened Ni-based superalloys in a hydrogen containing environment, and provide practical methods to mitigate the adverse effect of TBs on the performance of these alloys. Coherent twin boundaries in nickel-based superalloys are vulnerable sites for alloy failure in demanding environments. Here, the authors show that the abnormal γ″ precipitation mechanism at twin boundaries is responsible for pronounced strain localisation and subsequent failure. [ABSTRACT FROM AUTHOR]