Microstructural characterization, mechanical property and corrosion behavior of VNbMoTaWAl refractory high entropy alloy coatings: Effect of Al content

Recently, the refractory high entropy alloy coatings have drawn lots of attention due to their high temperature strength and stable thermal properties. In this study, the VNbMoTaW and three Al contained VNbMoTaWAl refractory high entropy alloy coatings were fabricated using a pulsed direct current magnetron co-sputtering system. Al addition into the VNbMoTaW coatings was chosen for this study since Al is an important material known for its lightweight. The BCC phase of the VNbMoTaWAl coating was kept as 8.54 at.% Al was added. The surface roughness, grain size and density of VNbMoTaW and VNbMoTaWAl coatings decreased with increasing Al content. The addition of Al element into VNbMoTaW coating can increase its hardness up to 18.1 GPa due to the solution hardening effect. The corrosion resistance of the 304 stainless steel substrate in 0.5 M H₂SO₄ solution was improved by the refractory VNbMoTaW and VNbMoTaWAl coatings. Furthermore, the best corrosion resistance of VNbMoTaWAl coatings was obtained by the addition of 2.37 at.% Al. The equivalent circuit of the VNbMoTaWAl coatings in 0.5 M H₂SO₄ solution was also proposed. However, the oxygen contamination in excess of 3 at.% in the VNbMoTaWAl coatings had detrimental effects on the mechanical properties and corrosion resistance of the coatings due to formation of oxide phases.