Lattice misfit-dominated solid solution strengthening in V-Nb-Ta-Ti refractory multi-principal element alloys demonstrated by high-throughput characterization

Abstract

This study investigates the solid solution strengthening (SSS) mechanisms in refractory multi-principal element alloys (RMPEAs) by developing a novel cladding melting-diffusion synthesis strategy. This strategy enables the fabrication of gradient-composition diffusion couples within the V-Nb-Ta-Ti system, effectively alleviating experimental uncertainties arising from variations in interstitial impurities and grain orientations across different samples. Comparative analyses of two representative binary couples, i.e., VNb (featuring significant lattice mismatch but minor modulus mismatch) and NbTa (exhibiting minor lattice mismatch but significant modulus mismatch), reveal that lattice mismatch predominates the SSS effects in this alloy system. Furthermore, predictions based on the Toda-Caraballo model are compared with the nanoindentation measurements, underscoring the substantial impact of V addition owing to its pronounced lattice mismatch with other principal elements. Consequently, peak hardness (∼5.0 GPa) is observed near the V₅₀Nb₂₅Ta₂₅ composition. Although the direct contribution of modulus mismatch to SSS is determined to be marginal in this system, its synergistic incorporation enhances the model's predictive accuracy. Tensile tests conducted on typical equiatomic alloys yield results consistent with nanoindentation data. Moreover, by analyzing over 700 nanoindentation data points, the optimal dislocation proportionality coefficient is determined as α = 9. This work proposes an effective high-throughput method for investigating compositional effects in alloys sensitive to interstitial impurities, and unveil the key mechanism governing SSS in V-Nb-Ta-Ti RMPEAs, thereby providing valuable guidance for future alloy design.