Ranking of refractory high-entropy alloys-based coatings for hot-forging dies

High Entropy Alloys (HEAs) are prominent materials of interest over the past two decades, of late veer towards Refractory High Entropy Alloys (RHEAs) suitable as coatings for conventional hot forging die materials, viz., Uddeholm Dievar, H13, and others, having a superior combination of properties including ambient- and elevated-temperature mechanical properties, including wear, thermal and strength properties, and degradation resistance. The RHEAs are potential competitors to the current conventional coatings for forging dies. We analyzed the RHEAs available in the current literature using decision science and data-driven techniques, including multiple attribute decision making (MADM) for sorting and ranking the RHEAs, Principal Component Analyses (PCA), for consolidating the ranks, and Hierarchical Clustering (HC) for identifying similarities among the top-ranked alloys. The ranks assigned by several MADMs, viz including ARAS (Additive Ratio Assessment), MAUT (Multi-Attribute Utility Theory), MOORA (Multi Objective Optimization On the basis of Ratio Analysis), ROVM (Range Of Value Method), TOPSIS (Technique of Order Preference by Similarity to Ideal Solution), and WEDBA (Weighted Euclidean Distance Based Approach), were consistent; in fact the Spearman's correlation coefficients (S_ρ) was > 0.80! The investigation identified RHEAs’ potential as coatings for hot-forging dies, identified top RHEAs having properties significantly superior to the current benchmark, and suggested directives for further development. Specifically, the top-ranked RHEAs, Al_20.4-Mo_10.5-Nb_22.4-Ta_10.1-Ti_17.8-Zr_18.8 and Ti₂₀-Zr₂₀-Hf₂₀-Nb₂₀-Cr₂₀, have far superior properties like low wear rate (associated with the BCC structure of these two RHEAs), thermal conductivity < 75 W/mK, and yield strengths, at ambient and elevated temperatures (up to 800C), > 1300 MPa compared to the conventional hot forging die materials. Thus, these RHEAs are very attractive as coating materials for the dies to forge high-temperature alloys in a cost-effective way with improved die life. The analysis also reveals the alloy design strategy for further development of even superior RHEA-based coatings.