Hot corrosion behavior of TiAlN single-layer and thick Ti/TiAlN multilayer coatings at 700 °C

Thick Ti/TiAlN multilayer coatings consisted of the periodic introduction of Ti layers into TiAlN layers were prepared onto TC4 titanium alloy substrates by arc ion plating. The results indicated that the thick corrosion product layer, which consisted primarily of Na2Ti9O19 and Al2O3, formed on the surface of the TiAlN single-layer coating in localized regions. The thermal stress and high brittleness of the thick ceramic nitride coating led to cracking of the TiAlN single-layer coating, exacerbating the hot corrosion. The corrosion products of the Ti/TiAlN multilayer coatings were composed of sodium salts, TiO2, and Al2O3. The less mass gain, the thin corrosion product layer, and slight internal oxidation demonstrated the reasonable hot corrosion resistance of the multilayer coating with a thin Ti sublayer. In contrast, the most weight gain, the thick product layer, and severe internal oxidation of the sublayers indicated the inferior corrosion resistance of the multilayer coating with a thick Ti layer. The presence of droplet defects, columnar grain boundaries, and microcellular corrosion led to the severe internal oxidation of the thick Ti sublayers.