Investigation of slurry erosion-corrosion behavior of Ta(Si 1-x Al x ) 2 nanocrystalline coatings

To enhance the erosion-corrosion resistance of titanium alloys, two Ta(Si1-xAlx)2 coatings with different Al content were deposited on Ti-6Al-4V alloy by double cathode glow discharge method. The coatings consist of single hexagonal C40 structured TaSi2 phase, which forms an equiaxed grain structure with an average diameter of ~5 nm. Al addition was found to enhance the values of H/E and adhesive strength between the substrate and coating. The erosion–corrosion behavior of the coatings was studied in a liquid–solid acid slurry flow (specifically a medium of 5 wt.% HCl solution that contained a 10 wt.% concentration of silica-based sand) using electrochemical measurements, weight loss tests and SEM observation. The results indicated that the ternary Ta(Si0.875Al0.125)2 coating provided better protection, compared to the binary TaSi2 coating, against the combined attack of mechanical erosion and electrochemical corrosion in a liquid–solid acid slurry flow. This is attributable to high self-healing ability of the surface passive film and a higher H/E ratio.