Surface protection of a V-4Cr-4Ti alloy through a multilayered TiAl/TiAlN composite coating

The vanadium alloys are attractive structural materials for applications in Generation IV reactors and fusion reactors. Surface protections of the alloy are required due to its high affinity to H, O etc. impurity atoms. The previous coating designs on the vanadium alloys have been focused on monolithic coatings and may have low coating-substrate bonding strengths. The TiAlN-based composite coatings which show remarkable surface protection effects, are yet to be applied to the vanadium alloy substrates. In the current work, a TiAl/TiAlN composite coating with intermediate TiAl layers was deposited on a V-4Cr-4Ti alloy substrate using the filtered-cathodic vacuum-arc-deposition (FCVAD) method. The coating with a total thickness of ∼18 μm was compact and free of any voids or inclusions. A high adherence strength of ∼82 N was measured for the coating. The ultrafine equi-axed γ-TiAl grains in the TiAl layer, and the columnar grains in the TiAlN layer which are composed of a mixture of TiN/AlN/Ti3AlN phases were characterized in detail with the transmission electron microscopy (TEM). The surface hardness and surface roughness were significantly improved for the coating compared with the substrate. The electrochemical corrosion results also show that the composite coating offers improved corrosion resistance against aqueous corrosion at room temperature.