Evolution of grain boundaries in multi-principal alloys: Insights into phase stability and structural complexity

Investigating the diffusion mechanism of Multi-principal element alloys (MPEAs) is crucial for understanding their exceptional utilization in energy storage systems. In this work, we employ a combined experimental and theoretical approach comprising of high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS), and density functional theory (DFT) calculations to study Pt, Cu, Ir, and Ni diffusion across multiple grain-boundary (GB) orientations in a Pt–Cu–Ir–Ni MPEAs. By integrating atomistic details from high-resolution microscopy into the first-principles simulations, our study shows how multielement compositions disrupt ordered structures, reduce local energy barriers, and create new diffusion pathways. The nudged elastic band method is used to compute activation barriers, revealing a range from as low as 0.57 eV (Cu) to around 2.82 eV (Pt) in certain GB configurations. Using these activation energies, diffusion coefficients were estimated to assess temperature-dependent behavior. The results show significant differences in atomic mobility among elements and confirm strong thermal activation of GB diffusion. Such enhancements in atomic mobility help explain key MPEA properties, improved sintering potential, grain coalescence, and retention of mechanical stability under harsh operating conditions, all of which are linked to the interplay of different elements at GBs. These findings bridge critical knowledge gaps in the field of multi-component alloys, providing actionable insights for tuning diffusion-driven processes such as microstructure refinement, creep resistance, and fatigue life.