Strategic Selection of Refractory High-Entropy Alloy Coatings for Hot-Forging Dies by Applying Decision Science

Abstract

We compiled, assessed, and ranked refractory high-entropy alloys (RHEAs) from the existing literature to identify promising coating materials for hot-forging dies. The selection methodology was rigorously guided by decision science principles, seamlessly integrating multiple attribute decision making (MADM), principal component analysis (PCA), and hierarchical clustering (HC). By employing a combination of twelve diverse MADM methods, we successfully ranked a total of 22 RHEAs. This analytical technique unveiled the top five RHEAs: Ti20-Zr20-Hf20-Nb20-Cr20, Al20.4-Mo10.5-Nb22.4-Ta10.1-Ti17.8-Zr18.8, Ti20-Zr20-Hf20-Nb20-V20, Al11.3-Nb22.3-Ta13.1-Ti27.9-V4.5-Zr20.9, and Al7.9-Hf12.8-Nb23-Ta16.8-Ti18.9-Zr20.6 pertinent for generating data on other significant properties, including wear resistance, fatigue (both thermal and mechanical), bonding compatibility with the substrate die material, oxidation resistance, potential reactions with the workpiece, cost-effectiveness, fabricability, and more. The three highest-ranked RHEAs share key characteristics, including a body-centered cubic (BCC) crystal structure, thermal conductivity below ~70 W/mK, and impressive yield strength at ambient and elevated temperatures, surpassing 1100 MPa. Moreover, they exhibit a remarkable ~73% similarity among themselves. The decision science-driven analyses yield sound metallurgical insights and provide valuable guidelines for developing RHEA coatings tailored for hot-forging dies. The strategy for designing RHEA-based coating materials for hot-forging dies should focus on compositions featuring a substantial presence of refractory metals while maintaining a BCC crystal structure. This combination is likely to deliver the desired blend of thermal and mechanical properties, rendering these coatings exceptionally well-suited for the demanding requirements of hot-forging operations.

Decision Science-Driven Assessment of Ti Alloys for Aircraft Landing Gear Beams

“…Applying Ashby techniques, the selection was narrowed down to metastable β, a few near-β, some α + β, and near-α Ti alloys as possible alloys [28]. After narrowing down a set of alloys, it is prudent to rank these alloys or variants (including the research alloys) based on some simple but important properties or attributes, select the top-ranked alloys or variants, and then generate all the data required extensively in a quicker and more cost-effective and sensible way on those limited top ranked alloys/variants than evaluating every alloy for all the requirements for a targeted application in that class, as described elsewhere [29][30][31][32][33]. The typical benchmark (or goal requirements) for landing gear applications includes yield strength ≥ ~1250 MPa, ultimate tensile strength ≥ ~1300 MPa, elongation ≥ ~5%, fatigue limit ≥ ~620 MPa, fracture toughness ≥ ~45 MPam 1/2 , and so forth [7][8][9]27].…”