Insight into the transformation of sand erosion damage evolution with varying bi-layer periods in TiN/Ti coatings

To explore the influences of micron scale bi-layer period on the sand erosion behaviors of ceramic/metal multilayer coatings, TiN/Ti coatings with the same thickness (∼20 μm) but different bi-layer periods of 10 μm, 5 μm and 2.5 μm were fabricated. Their microstructures, mechanical properties and sand erosion behaviors at 130 m/s and 90° were elaborately investigated. The results showed the bi-layer period played an important role in the microstructure of TiN/Ti coatings and the P5 coating exhibited the best surface quality. With decreasing bi-layer period, the hardness, H 3 /E 2 and residual stress of coatings decreased, while the crack resistance and erosion performance increased firstly and then decreased. Deposition defects were the crucial reasons for both early micro-peelings and premature failure of coatings in sand erosion conditions. Moreover, the micron scale bi-layer period played an important role in the erosion behaviors of TiN/Ti coatings. Therein, the thickness of ceramic TiN sublayers mainly affected the crack resistance, thus determining the erosion damage threshold of TiN/Ti coatings. The thickness of metal Ti sublayers mainly impacted on the crack propagation characteristics, thus determining the erosion damage evolution of TiN/Ti coatings. Attributing to the ceramic sublayers with excellent crack resistance and the metal sublayers hindering cracks longitudinal propagation, the P5 coating exhibited the best erosion resistance featuring the longest erosion duration of 200 minutes and the lowest erosion rate of 0.0067 mg/g. As the bi-layer period decreased from 10 μm to 2.5 μm, the erosion damage evolution of TiN/Ti coatings transformed from a progressive layer-by-layer failure featuring thin micro-peelings to a dramatically rapid failure with blocky spalling spanning multilayers.