J. Li; Y. Li; M. Hassani
Surface and Coatings Technology 496 (2025) 131669
Melt-based processing of refractory high-entropy alloy (RHEA) coatings is challenging due to the significant mismatches in thermo-physical properties among the principal refractory elements. While mechanically driven methods can minimize these issues, the chemical mixing and phase formation mechanisms at the atomic scale remain elusive. Here, we synthesize TiVZrTa RHEA coatings on a steel substrate via surface mechanical alloying and consolidation (SMAC). We study the formation mechanisms of the RHEA coatings under both cryogenic (−196 °C) and room temperature (RT) processing. Energy dispersive spectroscopy and X-ray diffraction measurements reveal a gradual absorption of elements into the Ta or V lattices during the coating formation for both conditions. While RT processed RHEA exhibits a multi-phase microstructure, cryogenic processing offers more effective and homogeneous mixing, producing a nearly single-phase BCC solid solution. Our kinetic Monte Carlo (kMC) simulations effectively reproduce the chemical mixing states during the phase formation of the TiVZrTa RHEA coatings. We report that the high homogeneity of the cryogenic temperature (CT) processed RHEA coating is due to the suppressed dynamic recovery and enhanced mechanical shearing. The CT processed RHEA coating exhibits an average hardness up to ∼13 GPa, around 30 % increase compared to that of the RT counterparts. We attribute this high hardness to more pronounced grain boundary strengthening and solute strengthening in the CT processed coating.