Solute strengthening in random alloys

Abstract

Random solid solution alloys are a broad class of materials that are used across the entire spectrum of engineering metals, whether as stand-alone materials (e.g. Al-5xxx alloys) or as the matrix in precipitatestrengthening materials (e.g. Ni-based superalloys). As a result, the mechanisms of, and prediction of, strengthening in solid solutions has a long history. Many concepts have been developed and important trends identified but predictive capability has remained elusive. In recent years, a new theory has been developed that builds on one historical model, the Labusch model, in important ways that lead to a well-defined model valid for random solutions with arbitrary numbers of components and compositions. The new theory uses first-principles-computed solute/dislocation interaction energies as input, from which specific predictions emerge for the yield strength and activation volume as a function of alloy composition, temperature, and strain-rate. Being a general model for materials that otherwise have a low Peierls stress, it has broad application and has been successfully applied to Al-X alloys, Mg-Al, twinning in Mg alloys, and recently fcc High-Entropy Alloys. Here, the new theory is presented in a general and systematic manner. Approximations and limiting cases that reduce the complexity and facilitate understanding are introduced, and help relate the new model to various physical features present among the historical array of models. The quantitative predictions of the model in the various materials above is then demonstrated.

Effect of solute content and temperature on the deformation mechanisms and critical resolved shear stress in Mg-Al and Mg-Zn alloys

“…where c is the solute element content (in at. %) and K is a constant that depends on the alloying element and temperature [44,46]. The experimentally determined strengthening in CRSS at 373 K of Fig.…”

Strengthening of high entropy alloys by dilute solute additions: CoCrFeNiAl and CoCrFeNiMnAl alloys

“…The full theory for the finite-T , finite-strain-rate initial yield strength of arbitrary random fcc alloys has been presented in Refs. [14,17]. The theory treats the random alloy as a high-concentration solute-strengthened alloy in which each elemental component is a "solute" within an "effectivemedium matrix" describing the average alloy properties [14,18].…”

“…Strengthening is due to the interactions of dislocations in the effective matrix with the spatial concentration fluctuations of the multi-component random alloy. The full theory includes all solute/dislocation interaction effects through the general interaction energy U n (x i , y j ) for a solute at position (x i , y j ) relative to the center of the dislocation line [17]. The full theory can be reduced to an analytical model when the solute/dislocation interactions are described by elasticity, as U n (x i , y j ) = −p(x i , y j )∆V n where ∆V n is the misfit volume of the solute n at concentration c n in the N -component alloy and p(x i , y j ) is the elastic pressure field generated by the dislocation into the "effective medium matrix" at position (x i , y j ).…”

Study on Porous Mg-Zn-Zr ZK61 Alloys Produced by Laser Additive Manufacturing

“…Secondly, with the increasing Zn content, the solubility of Zn in α-Mg matrix increases. On the basis of the solid solution strengthening theory [47], high solid solubility will induce excellent properties. For Mg-Zn-Zr alloys, the microhardness value is proportional to the solid solubility of Zn in α-Mg, therefore, solid solution strengthening is conductive to the increase of the microhardness as well.…”