Investigation of slurry erosion-corrosion behavior of Ta(Si1−xAlx)2 nanocrystalline coatings

Abstract

To enhance the erosion-corrosion resistance of titanium alloys, two Ta(Si _1−x Al _x ) _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 TaSi _2 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(Si _0.875 Al _0.125 ) _2 coating provided better protection, compared to the binary TaSi _2 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.

Keywords

• erosion-corrosion
• refractory metal silicides
• slurry flow
• EIS
• mechanical properties