In this study, monolayer TiN and multilayer TiN/Ti coatings involving different modulation ratios were deposited on Ti-6Al-4V substrate. Ti interlayers in the multilayer TiN/Ti coatings were prepared under gradient negative bias of -800, -600, and -400 V, with corresponding durations of 2, 2, and 1 min. Mechanical properties and crack' s resistance of the coatings were explored. Damage morphology of coating cross-section was characterized by the focused ion beam (FIB) method. Finite element modelling was used to analyse the stress field. Multilayer TiN/Ti coatings show better impact resistance than monolayer TiN coating. Tensile stress decrease with the increase of interfaces. Gradient bias Ti interlayers restrain crack propagation by cracks deflection and branch. Erosion resistance was evaluated by sand erosion test. Crack propagation and connection account for the coatings failure: the deeper the crack propagation, the higher the erosion rate.

Sand erosion is a major factor that shortens the service life of aircraft in desert regions. The anti-erosion performance of titanium alloys may be improved using TiN coatings. However, few studies have employed Ti sputtering on Ti transition layers to improve the erosion resistance of the coatings. Herein, TiN coatings with a sputtering layer between the Ti transition layer and the TiN layer were deposited on a Ti-6Al-4V alloy by filtered cathodic vacuum arc deposition. For comparison, another group of TiN coatings without a Ti sputtering layer but processed using the same deposition parameters were prepared. The effects of the nanoscale sputtering layer on the microstructure, mechanical properties, and anti-erosion performance of the coatings were investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nanoindentation. The results show that the introduction of a Ti sputtering layer promoted the growth of TiN grains, leading to the formation of finer and denser TiN columnar grains. The preferred orientation of the coatings with the sputtering layer is (111) plane, whereas that of the coatings without the sputtering layer is (200) plane. The TiN coatings containing a sputtering layer exhibit higher hardness, elastic modulus, and H 3 /E 2 ratio, which enhances the anti-erosion performance of the coatings. The coatings with a sputtering layer exhibited better erosion resistance (erosion rate reduced by 75%) than the coatings without a sputtering layer. The underlying mechanism to understand the effect of the sputtering layer on the erosion resistance was discussed based on variations in the microstructure and mechanical properties of the coatings with and without the Ti sputtering layer. Ti sputtering layer was finally proved to be an effective method to improve the erosion resistance of TiN coatings.

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Sand erosion has always been a key threat to the performance and service life of aero-engines. The compressor, the key component installed at the front of the aero-engine, suffers the most from sand erosion, especially compressors serving in deserts. Ceramic hard coating is a traditional way to improve the hardness and wear resistance of cutting and grinding tools. It may also be used to improve the erosion resistance of aero- engine compressor. However, the mechanism of erosion damage is complicated, which may include wear, secondary erosion, anisotropic erosion, impact, and fatigue. Recent research discovered the major problems with ceramic hard coating on aero-engine compressors. In this paper, these following problems are discussed: the design of coating material and structure, the preparation method and technology, the effects of droplets and clusters of coating surface, microstructure and characteristics of interface. The review of the major problems and possible solutions discussed in this paper may contribute to the future research on erosion coating theoretically and practically.

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