Sand particle erosion resistance of the multilayer gradient TiN/Ti coatings on Ti6Al4V alloy

Abstract Multilayer gradient TiN/Ti (MLG-TiN/Ti) and multilayer TiN/Ti (ML-TiN/Ti) coatings with different layer numbers were deposited on Ti6Al4V alloy by filtered cathodic vacuum arc technique (FCVA) to improve the erosion resistance of the substrates. Scan electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and nanoindentation were used to examine the microstructural and mechanical properties of the as-deposited coatings. The erosion resistance of these coatings was evaluated with home-made erosion tester. Though the two types of coatings showed similar grain structure, the finer grain sizes and higher hardness were obtained for MLG-TiN/Ti coatings. The structure parameters had a significant influence on erosion resistance. The coating MLG-4 with total thickness 12.09 μm exhibited the lowest erosion rate both among MLG-TiN/Ti and ML-TiN/Ti coatings. It contains two TiN layers, two Ti layers and three gradient layers and the thickness ratio of these three kinds of the layer is 9:1:1. The gradient layers, which can restrain the propagation of lateral cracks, formed in MLG-TiN/Ti coatings made the contribution to the great improvement of the erosion resistance of MLG-TiN/Ti comparing with ML-TiN/Ti coatings.