Unravel hardening mechanism of AlCrNbSiTi high-entropy alloy coatings

Abstract

Novel high-entropy alloys (HEAs) coatings deposited using physical vapour deposition technique are potential candidates of protective coatings due to their excellent performance. However, the correlation between properties and microstructure of HEAs coatings has not been completely established and the hardening mechanism remains unclear. In this paper, the AlCrNbSiTi HEA coatings were deposited under different bias voltages by radio-frequency magnetron sputtering. The morphology, chemical composition, structure, mechanical properties and thermal stability are discussed in detail. All coatings exhibit smooth surface without obvious elemental segregation and the columnar structure tends to densify with increasing bias. The coatings possess a nanocomposite structure of amorphous-nanocrystalline silicides, in agreement with the results calculated based on three phase prediction parameters (ΔHmix: enthalpy of mixing, δ: atomic size difference and Ω: ratio of entropy of mixing ΔSmix to ΔHmix). The coating deposited at bias of − 50 V presents optimal mechanical properties with nanohardness of ∼15.2 GPa, scratch crack propagation resistance of 1042 N2 and wear rate of 5.4 × 10−8 mm3N−1m−1. Annealing treatment further unravels that the presence of hard silicides is the hardening mechanism of coatings with super-hardness of ∼24 GPa. The results indicate that the AlCrNbSiTi coating is a promising protective coating with broad industrial application prospects.