Research on the densification behavior, microstructure evolution and interface optimization of cold sprayed Ti6Al4V coatings

To address the problems of high porosity and poor adhesion strength existing in Ti6Al4V coatings prepared by cold spraying technology, the strategy of in-situ laser and micro-forging assistance for cold spraying was proposed in this study. The Ti6Al4V coatings with high relative density and high adhesion strength were successfully prepared, and the microstructure, interfacial strengthening mechanism, bending properties and failure behavior of the coatings were systematically analyzed. With N2 used as the propelling gas, under the spraying parameters of gas temperature at 800°C and gas pressure at 4 MPa, the Ti6Al4V coating has achieved a relative density of 99.77% and an adhesion strength exceeding 68.48 MPa. The Ti6Al4V powder within the coating undergoes severe plastic deformation, leading to a uniform microstructure without defects. A continuous and dense diffusion layer, with a thickness of 5-10 μm, is formed between the coating and substrate, primarily composed of α-Ti, β-Ti, TiN, TiC, FeTi and Fe2Ti phases. The metallurgical bonding between the coating and substrate significantly enhances the adhesion strength of the coating. The bending yield strength and flexural strength of the Ti6Al4V coating-protected Q235 substrate are 427.37 MPa and 770.76 MPa, respectively. Compared with the uncoated Q235 substrate, the bending yield strength and flexural strength of the Ti6Al4V coating-protected Q235 substrate increase by 41.6% and 26.9%, respectively, demonstrating that the introduction of the coating can significantly enhance the flexural performance of the substrate. The fracture morphology of the Ti6Al4V coating after the bending test exhibits ductile fracture characteristics, which accounted for the significant improvement in bending yield strength. The interfacial fracture between the coating and substrate shows quasi-cleavage characteristics, and the high bonding strength at the coating-substrate interface contributed to the enhancement of the substrate's flexural strength. Thus, the in-situ first-layer laser-assisted and subsequent-layer micro-forging assisted cold spraying have provided a feasible solution for the preparation of high-performance protective titanium-based coatings.