Atomistic and data-driven insights into the local slip resistances in random refractory multi-principal element alloys

TL;DR

This work addresses the challenge of understanding plastic deformation in refractory multi-principal element alloys (RMPEAs) by quantifying local slip resistance (LSR) for edge and screw dislocations on key BCC slip planes via atomistic statics. It pairs these atomistic insights with an autoencoder–random forest data‑driven framework to relate LSR to fundamental properties (e.g., lattice distortion, elastic constants, stacking-fault energies) and to develop a thermally activated, dislocation‑based yield model that predicts tensile strength across grain sizes $d$, temperatures $T$, and strain rates $\dot{\varepsilon}$. Key findings show that a high fraction of hexagonal close-packed (HCP) elements ($>50\%$) lowers USFE, ISS, and LSR, and that elastic anisotropy (Zener ratio $A_c$) similarly reduces these quantities, with lattice distortion modulating dislocation anisotropy. The authors identify elastic constants and lattice distortion as dominant LSR controls and demonstrate that their framework accurately predicts yield stress in BCC RMPEAs, providing a principled design pathway for high-temperature strength without sacrificing ductility.

Abstract

Refractory multi-principal element alloys (RMPEAs) have attracted growing interest for their exceptional high-temperature strength, yet their complex compositions hinder a mechanistic understanding of plastic deformation. Here, we perform atomistic simulations to determine local slip resistances (LSRs) of edge and screw dislocations on primary BCC slip planes in 12 equal-molar RMPEAs. Machine learning is employed to uncover relationships between LSR and underlying material properties, enabling systematic assessment of compositional effects on dislocation behavior. Based on these insights, we develop a thermally activated, dislocation-based model to predict macroscopic yield stress. We find that increasing the fraction of hexagonal close-packed elements above 50% significantly reduces unstable stacking fault energy, ideal shear strength, and screw LSR across all slip planes. Higher elastic anisotropy further lowers these quantities, while lattice distortion modifies relative slip resistances between dislocation characters and slip systems. By combining an autoencoder with a random forest model, we identify elastic constants and lattice distortion as the dominant factors controlling LSR. The resulting framework accurately predicts tensile yield stress in BCC RMPEAs and provides guidance for alloy design.

Figures (15)

• Figure 1: The schematic for local slip resistance (LSR) calculations. The dislocation line, its glide plane and Burgers vector on this plane are denoted by blue line, light-orange parallelogram and red arrow, respectively. The dislocation line and the normal of its glide plane are along $z$ and $y$ axes, respectively. For edge dislocation, the character angle $\theta$ between dislocation line and Burgers vector is $90^\circ$, while for screw dislocation, $0^\circ$.
• Figure 1: Comparison of theoretical yield-strength predictions and experimental measurements for seven RMPEAs when the six interaction coefficients $a_i$ in \ref{['equ:YS']} are set to a single parameter instead of a context-dependent function.
• Figure 2: The average GSFE curves of 12 RMPEAs on (a) $\{110\}$, (b) $\{112\}$, and (c) $\{123\}$ slip planes based on MS simulations. Each curve contains 101 data points; error bars represent the standard deviation derived from 20 independent samples per point.
• Figure 3: The mean values of (a) USFE ($\gamma_{\mathrm{usf}}$) and (b) ISS ($\tau_{\mathrm{iss}}$) of 12 RMPEAs for $\{110\}$, $\{112\}$, and $\{123\}$ slip planes. Error bars represent the standard deviation derived from 20 independent samples per RMPEA.
• Figure 4: The (a) LD coefficient ($\delta$), (b) USFE ($\gamma_{\mathrm{usf}}$) and (c) ISS ($\tau_{\mathrm{iss}}$) as a function of Zener ratio ($A_{\rm c}$) for 12 RMPEAs. $\{110\}$, $\{112\}$, and $\{123\}$ represent three slip planes.