NiCrAlY coating was deposited on TC4 (Ti-6Al-4V) titanium alloy substrate by arc ion plating (AIP). After vacuum heat treatments, the microstructures and microhardness of the NiCrAlY coating were characterized by using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and Vickers hardness test. The formation of interfacial products and the behavior of Cr element in TC4 substrate/NiCrAlY coating interface reactions were also studied. The results show that gamma'-Ni3Al phase precipitated in NiCrAlY coating after heat treatment, which increased the microhardness of the coating. After vacuum heat treatments under 870 degrees C, the effected zone, Ti2Ni layer, TiNi layer, and Ni-3(Al, Ti) layer appeared in turn from inside to outside at the interface between TC4 substrate and NiCrAlY coating. When the vacuum heat treatment temperature was above 870 degrees C, the Cr element began to diffuse and then reacted with Ti to form TiCr2. (C) 2007 Elsevier B.V. All rights reserved.