Effect of Surface Treatment of Electron-Beam-Melted Ti–6Al–4V Alloy with a TiN Coating on Resistance to Hydrogenation

In this work, the effect of the type of mechanical treatment of the surface of titanium alloy Ti–6Al–4V obtained by electron-beam melting before the magnetron deposition of a titanium nitride (TiN) coating on its resistance to hydrogenation at a test temperature of 560°C and a hydrogen pressure of 2 atm is studied. Sandblasting and mechanical grinding/polishing of Ti–6Al–4V alloy are used as surface-preparation procedures for experimental samples. It is found that a TiN coating (with a thickness of 1 μm) obtained using reactive magnetron sputtering can reduce hydrogenation of the titanium alloy by 18 times compared to the uncoated alloy when preliminary grinding/polishing of the sample surface to a roughness (R_a) of 0.05 μm is applied. For samples of polished Ti–6Al–4V alloy with a coating, after hydrogenation tests, a decrease in the coating hardness from 20.8 to 10.9 GPa and a noticeable decrease in the critical load, at which delamination of the coating occurs (from 28.4 to 19.2 N), are observed. When applying a TiN coating to the titanium-alloy surface after sandblasting, the β phase of titanium is stabilized, and titanium hydride TiH₂ is formed during Ti–6Al–4V-alloy hydrogenation.