TiC–Fe gradient coating on pure titanium fabricated by in-situ solid-phase diffusion: toward superior hardness and interfacial adhesion strength

Protective hard coatings can significantly improve the bottleneck problem of low hardness and poor wear resistance on titanium alloy surface. However, hardness and adhesive strength usually exhibit an inverse relationship, which greatly limits its widespread use. In this work, TiC–Fe gradient coating with high hardness and adhesion was successfully fabricated by in-situ solid-phase diffusion method (ISDM) on pure titanium at 1000 °C for 2 h. The average thickness of the coating was approximately 5 μm, and the volume fraction of TiC in the coating was greater than 95 vol%. The grain size of TiC gradually increased from 200 nm at the coating surface to 2 μm towards the substrate. The phase interface and the coating/substrate interface exhibited excellent interfacial bonding at the atomic scale. The novel TiC–Fe gradient coating can simultaneously achieve superior hardness (42.9 ± 2.6 GPa) and elastic modulus (557.4 ± 10.3 GPa) that is mainly dominated by in situ synthesised high volume fraction TiC, as well as high adhesion strength (>225 ± 10 MPa). The increased adhesion strength was attributed to the excellent macro/micro interfaces and gradient transition of the microstructure. The use of ISDM to fabricate TiC–Fe gradient coating on titanium alloy may provide a new strategy to improve the comprehensive properties including hardness, elastic modulus, interfacial adhesion strength, and wear resistance for wider applications.