Mastering Complexity toward High-Performance Multi-Principal Element Alloy-Based Films and Coatings: A Review on Microstructural Regulation and Property Optimization.

Multi-principal element alloy (MPEA)-based films and coatings are redefining the boundaries of materials science, offering an unprecedented synergy of mechanical robustness, thermal stability, and chemical resilience. Their performance arises from intrinsic chemical complexity, such as high configurational entropy, lattice distortion, sluggish diffusion, and synergistic elemental interactions, enabling the formation of refined microstructures and positioning them as ideal candidates for high-performance applications in extreme environments. This review provides a comprehensive exploration of microstructure regulation strategies for MPEA-based films and coatings, with a focus on the interplay between elemental composition, nanoscale architecture, heterostructures, and interfacial engineering in tailoring their properties and functions. A systematic analysis of their mechanical properties, alongside corrosion tolerance, wear and erosion resistance, and thermal stability is presented, while the fundamental mechanisms governing these exceptional performances are examined in depth. Additionally, their emerging and expanding applications in aerospace, biomedical, and extreme-environment technologies are highlighted, and chart their future, emphasizing the integration of multi-scale modeling, high-throughput synthesis, and machine learning-driven materials design to achieve predictive microstructure control and properties optimization. Finally, the challenges and opportunities that will shape the next era of high-performing MPEA-based films and coatings research are outlined, pushing the limits of what these extraordinary materials can achieve.