Pathways for ductility: Alloys containing multiple elements can be very strong but often suffer from poor ductility. F. Wang et al. found that different mechanisms accommodated plasticity in a molybdenum-niobium-titanium multiprincipal element alloy (see the Perspective by Cairney). Instead of so-called “screw” dislocations, deformation is accommodated by multiple pathways that include “edge” dislocations and activation of crystallographic slip planes. These results offer a design paradigm for developing new high-strength alloys. Science , this issue p. 95 ; see also p. 37

In this work, we use density functional theory to calculate the entire generalized stacking fault energy (GSFE) surface for eight transition metals with a face-centered cubic structure: Ag, Au, Cu, Ir, Ni, Pd, Pt, and Rh. Analysis of the $⟨112⟩$ GSFE curves finds that the displacements corresponding to the unstable stacking fault energy are larger than the ideal value for all eight metals except Ag and Cu. Over the entire surface, Pt is found to not possess well-defined local maxima or minima, suggesting spreading in favor of dissociation of the dislocation core, unlike the other seven metals. Our calculations also reveal that at a large $⟨112⟩$ displacement, where atoms on two {111} adjacent planes are aligned, an anomalous local minimum occurs for Ir and Rh. The oddity is explained by relatively large, localized atomic displacements that take place in the two metals to accommodate the alignment that do not occur in the other six metals. In addition to the fully calculated surfaces, we characterize a continuous 11-term Fourier-series function, which provides a particularly excellent representation of the GSFE surfaces for Ag, Au, Cu, Ni, and Pd.

Fe-Al compounds are of interest due to their combination of light weight, high strength, and wear and corrosion resistance, but new forms that are also ductile are needed for their widespread use. The challenge in developing Fe-Al compositions that are both lightweight and ductile lies in the intrinsic tradeoff between Al concentration and brittle-to-ductile transition temperature. Here, we show that a room-temperature, ductile-like response can be attained in a FeAl/FeAl₂ layered composite. Transmission electron microscopy, nanomechanical testing, and ab initio calculations find a critical layer thickness on the order of 1 μm, below which the FeAl₂ layer homogeneously codeforms with the FeAl layer. The FeAl₂ layer undergoes a fundamental change from multimodal, contained slip to unimodal slip that is aligned and fully transmitting across the FeAl/FeAl₂ interface. Lightweight Fe-Al alloys with room-temperature, ductile-like responses can inspire new applications in reactor systems and other structural applications for extreme environments.

We propose a new bubble dynamics model to study the evolution of a suspension of bubbles over a wide range of vesicularity, and that accounts for hydrodynamical interactions between bubbles while they grow, deform under shear flow conditions, and exchange mass by diffusion coarsening. The model is based on a lattice Boltzmann method for free surface flows. As such, it assumes an infinite viscosity contrast between the exsolved volatiles and the melt. Our model allows for coalescence when two bubbles approach each other because of growth or deformation. The parameter (disjoining pressure) that controls the coalescence efficiency, i.e., drainage time for the fluid film between the bubbles, can be set arbitrarily in our calculations. We calibrated this parameter by matching the measured time for the drainage of the melt film across a range of Bond numbers (ratio of buoyancy to surface tension stresses) with laboratory experiments of a bubble rising to a free surface. The model is then used successfully to model Ostwald ripening and bubble deformation under simple shear flow conditions. The results we obtain for the deformation of a single bubble are in excellent agreement with previous experimental and theoretical studies. For a suspension, we observe that the collective effect of bubbles is different depending on the relative magnitude of viscous and interfacial stresses (capillary number). At low capillary number, we find that bubbles deform more readily in a suspension than for the case of a single bubble, whereas the opposite is observed at high capillary number.