Silicon based coatings deposited by dynamic ion mixing for oxidation protection of a Ti6242 alloy

We have investigated the protective effect of SixCy and SixNy coatings deposited by dynamic ion mixing (DIM) on the oxidation resistance of a Ti6242 alloy (Ti-6Al-2Sn-4Zr-2Mo). The amorphous SixCy (x/y ∼ 1,1) and SixNy (x/y ∼ 2) coatings 0.25-0.21 μm thick respectively were produced by sputtering SiC and Si3N4 targets with a 1.2 keV Ar+ ion beam and the growing films were bombarded with 120 keV Ar+ ions. High precision thermogravimetry experiments were carried out at 600 °C in artificial air (20% O2 + 80% N2) during 100 h. A considerable reduction (∼ 2 orders of magnitude) of the oxidation rate is measured for both coatings independently of the surface roughness. The structural modifications consist principally in the formation of SiO2 at the surface and TiSi compounds at the interface. The increased oxidation resistance is discussed in relation with the intrinsic properties of the coatings and with the ion bombardment effect which improves the densification and induces interface mixing promoting coating adhesion.