Quantitative phase prediction in a eutectic AlCoCrFeNi2.1 high-entropy alloy HVOF coating using Scheil simulation
Ecio Bosi, Ashok Meghwal, Surinder Singh, Vladimir Luzin, Anthony Roccisano, Colin Hall, Paul Munroe, Christopher C. Berndt, Andrew Siao Ming Ang
Abstract
Eutectic high-entropy alloys (EHEAs) feature multiple distinct phases, unlike the single-phase solid solutions typical of conventional high-entropy alloys (HEAs). While EHEAs inherently consist of multiple phases, their performance as thermal spray coatings is directly influenced by their relative phase proportion and microstructural distribution, making phase control crucial for property optimization. While CALPHAD has been used to predict phases in HEAs, there remains a critical gap in its quantitative phase predictive capabilities, particularly for non-equilibrium cooling processes imitated by Scheil simulation. This study investigates Scheil simulation as a tool for both qualitative and quantitative phase prediction in the AlCoCrFeNi 2.1 EHEA HVOF (high velocity oxygen fuel) processed coating. The HVOF coating exhibited a deformed zone with unmelted and partially melted regions retaining the eutectic structure of the original powder, as well as a rapid solidified zone displaying a single-phase FCC solid solution. Phase fractions, determined by Rietveld analysis, closely matched those predicted by Scheil simulation - 66.7 wt% FCC and 32.3 wt% B2 versus experimental values of 72.7 ± 1.1 wt% FCC and 27.3 ± 1.1 wt% BCC/B2. Furthermore, the coating showed low microhardness and wear resistance, underscoring the limitations of FCC-rich microstructures for tribological applications. These results suggest that Scheil simulations can effectively aid the materials engineering design of EHEA thermal spray coatings. • Phase validation of HVOF-sprayed HEA coating using CALPHAD under rapid solidification. • Scheil simulation reliably predicts phase fractions in HVOF-sprayed EHEA coatings. • Eutectic powder microstructure is partially retained in the HVOF coating. • Dominant FCC phase provides intermediate hardness and limits wear resistance. • Abrasive wear and tribo-oxidation identified as primary wear mechanisms.