Tribocorrosion behaviors of VNbMoTaWCr high entropy alloy coatings

In this work, four BCC-structured VNbMoTaW and VNbMoTaWCr high entropy alloy (HEA) coatings with different Cr contents were fabricated on the surface of 304 stainless steel (304SS) plates by a pulsed DC magnetron sputtering system. In addition to the dry pin-on-disk wear test and pure corrosion test, two kinds of tribocorrosion tests were performed. For the tribocorrosion test without applied potential, the HEA coatings were immersed in a 3.5 wt% NaCl aqueous solution at room temperature under 1 N load using a pin-on-disk tribometer. For the tribocorrosion test with applied potentials, the potentiodynamic polarization test was conducted to investigate the effects of external potentials and sliding loads on the corrosion current density, polarization resistance, and wear rates of HEA coatings. The hardness, corrosion resistance, and tribocorrosion (without applied potential) resistance of VNbMoTaWCr HEA coatings increased with increasing Cr content. The VNbMoTaWCr coatings with higher than 24.7 at.% Cr had a high hardness of 16.4 to 16.5 GPa and excellent corrosion resistance in pure corrosion and tribocorrosion without applied potential. On the other hand, as the tribocorrosion was executed with an applied potential higher than the breakdown potential and high current density, the tribocorrosion resistance of HEA coatings was greatly influenced by its protection degradation ratio, Pdr (the polarization resistance ratio between pure corrosion and tribocorrosion setup 2). Finally, the lowest wear rate of 2.55 × 10−5 mm3N−1 m−1, which was 1.4 times better than 304SS, was obtained for the VNbMoTaWCr coating containing 11.65 at.% Cr after the tribocorrosion test with applied high potential because of its lower Pdr value and less decay of corrosion protection ability.