Mechanical properties of mullite/5wt% nano-fly ash feedstock powders produced using mechanical alloying methods for plasma spraying: Towards sustainable coating solutions

• Optimized wet ball milling at 60 r/min produces mullite/nano-fly ash feedstock powders with a uniform particle size of 14 µm, enhancing plasma spray deposition efficiency to 35%. • Wet-milled coatings exhibit significantly lower porosity (7.9%) and superior mechanical properties, including hardness of HV1 647 and fracture toughness of 1.41 MPa·m0.5. • Residual stress analysis reveals higher tensile stresses (up to 165.95 MPa) in wet-milled coatings due to finer particles and rapid thermal cycling, which may influence coating durability. • The study demonstrates a sustainable approach by repurposing fly ash, aligning with circular economy principles and reducing raw material consumption in coating applications.