Enhancing the cavitation erosion resistance of D8m-Ta5Si3 nanocrystalline coatings through Al alloying

Abstract

To investigate the effects of Al alloying on the erosion-corrosion resistance of β-Ta5Si3, both a β-Ta5Si3 coating and an Al-alloyed β-Ta5(Si0.83Al0.17)3 coating were synthesized on a 316 substrate by the double cathode glow discharge technique. The phase constitution, composition and microstructure of the two coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The two coatings were composed of nearly rounded D8m-β-Ta5Si3 grains with an average size of ∼4 nm, and after the addition of Al, the preferred growth orientation for the β-Ta5Si3 coating changed from (4 0 0) to (0 0 2). The hardness, elastic modulus and contact damage resistance of the coatings were measured using a nanoindentation tester. The results showed that Al alloying improved the contact damage resistance of β-Ta5Si3 with only a slight decrease in hardness. The erosion-corrosion behavior of the two coatings was performed in a 3.5 wt% NaCl solution containing a 12 wt% concentration of silica sand under two phase slurry flow condition and in a 3.5 wt% NaCl solution under ultrasonic cavitation erosion conditions. This revealed that the Al alloyed β-Ta5Si3 has a higher resistance to both erosion-corrosion and ultrasonic cavitation erosion as compared to the binary β-Ta5Si3 coating.