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

Abstract

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. 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 coatings have achieved a relative density of 99.77% and an adhesion strength exceeding 68.48 MPa. Severe plastic deformation was observed in the Ti6Al4V powder within the coatings. The coatings exhibited no evident porosity defects, and a continuous, dense diffusion layer with a thickness of 5–10 µm was formed between the coating and substrate, primarily composed of α-Ti, α-Ti, TiN, TiC, FeTi, and Fe₂Ti phases. The metallurgical bonding between the coating and substrate significantly enhances the adhesion strength of the coatings. The bending yield strength and flexural strength of the coating-protected Q235 substrate are 427.37 and 770.76 MPa, respectively. Compared with the uncoated Q235 substrate, the bending yield strength and flexural strength of the coating-protected Q235 substrate (with the coatings on the bottom) increase by 41.58% and 27.00%, respectively, demonstrating that the introduction of the coatings can significantly enhance the flexural performance of the substrate. The fracture morphology of the Ti6Al4V coatings 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 quasicleavage characteristics, and the high bonding strength at the coating-substrate interface contributes 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 has provided a feasible solution for the preparation of high-performance protective titanium-based coatings.

Keywords

in-situ laser-micro forging / cold spraying / Ti6Al4V coatings / adhesion strength / flexural properties

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