Role of scandium in mechanical alloying of AlCoCrFeMo high-entropy alloy powders for flame spray coating deposition

The growing demand for advanced materials that can withstand extreme conditions in aerospace, defence, and energy sectors has driven interests in high-entropy alloys (HEAs). This study investigates the doping of Scandium (Sc), a rare earth element, into AlCoCrFeMo HEA using mechanical alloying via ball milling. Sc has gained significant attention for promoting grain refinement by forming precipitates that act as nucleation sites, inhibit grain growth, and enhance grain structure, thereby enhancing mechanical strength and ductility. This study optimizes the mechanical alloying parameters to achieve a homogeneous distribution of Sc in the AlCoCrFeMo HEA matrix. Results indicated that 12 h of mechanical alloying at 110 rpm is sufficient to ensure uniform distribution of Sc in the HEA. Various Sc compositions (0.1 wt%, 0.3 wt%, and 0.5 wt%) were investigated to determine the solubility limit of Sc in the HEA. The microstructural and chemical composition analyses revealed that the Sc solubility limit in the HEA lies between 0.2 and 0.3 wt%, providing critical insights for alloy design. Flame-sprayed coatings from Sc-doped powders exhibited significant refined splat morphologies, reduced porosity, and increased hardness, achieving up to 979 HV 0.3 , demonstrating superior coating performance enabled by Sc incorporation. These findings provide critical insights into the behaviour of Sc-doped HEAs, supporting their deployment in extreme environments where superior mechanical performance is essential. • A mechanical alloying process was developed and optimized to dope scandium into AlCoCrFeMo high entropy alloy (HEA). • The solubility limit of Sc in AlCoCrFeMo HEA was identified between 0.2 and 0.3 wt%. • Flame-sprayed Sc-doped coatings exhibited refined microstructures and a reduced amount of porosity. • The optimized coatings reached a 104 % hardness improvement over the base HEA.