Solute misfit and solute interaction effects on strengthening: A case study in AuNi

AuNi is a classic long-studied fcc alloy combining a very "large" atom (Au) and a very "small" atom (Ni), and the large atomic size misfits suggest very high strengthening. Here, AuNi is used as a model alloy for the testing of new strengthening theories in random alloys that include the effects of both size misfits and solute–solute interactions. Experimentally, AuNi samples are fabricated, characterized, and tested, and show no segregation after annealing at 900 °C and a very high yield strength of 769 MPa. Theoretically, the main inputs to the theory (alloy lattice and elastic constants, solute misfit volumes, energy fluctuations associated with slip in the presence of solute–solute interactions) are extracted from experiments or computed using first-principles DFT. The parameter-free prediction of the yield strength is 809 MPa, in very good agreement with experiments. Solute–solute interactions enhance the strength only moderately (13%), demonstrating that the strengthening is dominated by the solute misfit contribution. Various aspects of the full theory are discussed, the general methodology is presented in an easy-to-apply analytic framework, and a new analysis for strengthening in alloys with zero misfits but non-zero solute–solute interactions is presented. These results provide support for the theories and point toward applications to many fcc complex concentrated alloys.

AuNi是一种经典且被长期研究的面心立方（face-centered cubic, fcc）合金，由尺寸“较大”的金（Au）与尺寸“较小”的镍（Ni）组成，原子尺寸错配程度极高，预示着极强的强化效应。本研究以AuNi作为模型合金，用于检验同时考虑尺寸错配与溶质-溶质相互作用的无序合金强化新理论。实验方面，研究人员制备并表征了AuNi合金试样并开展性能测试，结果显示该合金经900℃退火后无偏析现象，屈服强度高达769 MPa。理论层面，强化理论所需的核心输入参数（合金晶格与弹性常数、溶质错配体积、溶质-溶质相互作用下滑移相关的能量涨落）均通过实验提取或第一性原理密度泛函理论（density functional theory, DFT）计算得到。该理论的无参数预测屈服强度为809 MPa，与实验结果吻合度极佳。溶质-溶质相互作用仅使强度小幅提升（13%），表明强化效应主要由溶质错配贡献主导。本文对完整强化理论的多个维度展开讨论，以易于推广应用的解析框架呈现通用方法论，并针对错配为零但存在非零溶质-溶质相互作用的合金提出了全新的强化分析方法。上述结果为该强化理论提供了支撑，并有望应用于众多面心立方复杂成分合金体系。