High-entropy carbides designed to resist cavitation erosion-corrosion in an acidic environment: Surface engineering guided by first-principles calculations and experiments

In this study, the influence of chemical composition on phase stability, mechanical and electronic properties of (TixZr0.2Nb0.2Ta0.2Mo0.4-x)C (x = 0.3, 0.2, 0.1) high entropy carbide ceramics (HECCs) were first explored by first-principles calculations. The results showed that the composition (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C has higher values of electron work function (EWF) value and theoretical hardness than that of the other HECCs with lower Ti concentrations. Following this investigation, a (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C HECC coating was deposited onto a commercially pure titanium substrate by a reactive-sputtering method. The as-prepared HECC coating had a uniform thickness of ∼17 μm and consisted of equiaxed nanocrystals with a mean diameter of ∼7 nm. The cavitation erosion-corrosion behavior of the HECC coating was studied by combining electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) measurements in a 0.05 M H2SO4 solution. The EIS results revealed that with increasing time of cavitation exposure, the resistance value of the HECC coating was an order of magnitude larger than that for uncoated CP-Ti for a given cavitation time. EN analysis indicated that under cavitation conditions, uncoated CP-Ti was more vulnerable to localized corrosive attack than the HECC coating in an acidic environment.