Study on the interface reaction behavior of NiCrAlY coating on titanium alloy

NiCrAlY coating was deposited on TC4 (Ti-6Al-4V) titanium alloy substrate by arc ion plating (AIP). After vacuum heat treatments, the interface reaction behavior of NiCrAlY coating/TC4 substrate was studied. The results show that the 20 μm as-deposited coating, which was made up of γ-Ni, α-Cr and β-NiAl phases with 50-200 nm grain size, was continuous and tightly bound to the substrate. The allotropic transformation of α-Ti to β-Ti during the heat treatment had a significant influence on the interface reaction behavior. After vacuum heat treatment below the allotropic transformation temperature (ATT) of titanium, i.e. 750 °C, Ni3(Al, Ti)/TiNi/Ti2Ni/Ti3Al and α-Ti/β-Ti stabilized layer formed in turn from the coating to substrate at the interface. At 870 °C or 900 °C (near/above the ATT of titanium), Cr began to take part in the interface reaction and α-TiCr2 phase was detected. With the increase of heat treatment time at 900 °C, including the coating phases, all the interface products decomposed and solved in the substrate to form a thick β-Ti stabilized layer for the higher solid solubility of the coating elements in β-Ti. The decomposition of the coating led to its total degradation. The interface reaction processes were studied in terms of thermodynamic and kinetic factors. Based on Fick's first law, the relation between the thickness of interface reaction layer and heat treatment time was discussed.