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Solid particle erosion (SPE) resistance of compressor titanium alloy blade can be enhanced by the hard coatings. But the system of hard coating / soft substrate is easily corrupt by the SPE due to the coatings’ higher brittleness and interface mismatch, so the brittle fracture often occurs at the interface of coating and substrate. In order to improve the hard coatings’ SPE resistance, combining with the plasma ion diffusion and arc ion plating technology, a series of composite coatings with gradient carburized layer and TiN(Ti) coating were synthesized on TC4 alloy. And the influence of structure on composite coating’s properties was studied in detail. The results showed that the hardness and bonding strength of composite coatings were enhanced remarkably, comparing with the monolayer TiN and 12 periods of Ti/TiN hard coatings deposited on TC4 alloy without plasma carburization. The monolayer TiN showed a mechanism of brittle cracking after sand erosion, and the 12 periods of Ti/TiN coating presents morphologies of flaking and erosion pit due to the multilayer toughening effect. After carburization, the coating’s impact toughness was enhanced. The interface fracture of monolayer TiN was restrained. And the composite coating with gradient carburized layer and 12 periods of Ti/TiN coating possessed the best SPE resistance with erosion weight loss rate decreased by more than ten times and showed a mechanism of tough damage, which can be attributed to its higher interface strength and better match of hardness and toughness.