Effect of bias voltage on the erosion performance of TiAlSiN coatings on TC6 substrate by high power impulse magnetron sputtering

TiAlSiN coatings were deposited on TC6 substrates by high power impulse magnetron sputtering at various bias voltages for the improvement of titanium alloy anti-sand erosion performance. The effect of bias voltage on the composition, microstructure and mechanical properties were investigated by X-ray photoelectron spectroscopy, X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, Rockwell-C indentation, scratch testing and nano nanoindentation. The erosion performance was evaluated at the impingent angles of 30 degrees and 90 degrees respectively in a sand blasting tester. With the application and increase in bias voltage, the discharge current increases from -87 A to -210 A. The coatings exhibit face center cubic structure, mainly composed of the (Ti,Al)N nanocrystallites and Si3N4 matrix. The preferred orientation shifts from (200) to (220) in the range of 0--150 V, but goes back to (200) at -200 V. The surface nodular defects and deposition rate are gradually reduced, yet the sectional structure becomes much denser. The residual stress is compressive and continually grows, whereas the adhesion strength, hardness (H), Young's modulus (E) and H/E ratio gradually increase before decreasing, arriving at maximum values of -68 N, -37.53 GPa, -339.9 GPa and 0.11 respectively at -150 V. The erosion resistance of the TiAlSiN coatings is consistent with these mechanical changes at various bias voltages and is also optimal at -150 V, which is -14 times that of TC6 substrate. The failure mechanism comes from coating brittleness nature, fractured chips and microcracks, regardless sand erosion angles, yet the driving forces are different.