Local microstructure inhomogeneity and gas temperature effect in in-situ shot-peening assisted cold-sprayed Ti-6Al-4V coating

Highlights: • We prepared dense TC4 coating with a novel in-situ shot peening assisted cold-sprayed technology. • We focused on the local microstructure inhomogeneity and measured the porosity, microhardness and elastic modulus separately. • We modeled the mechanism to explain this special microstructure formed in in-situ shot peening assisted cold-spraying. • We found the law of the depth of shot blasting with the change of gas. In the cold spraying process, previously deposited particles are hammered by the following particles, and gas temperature plays an important role in coating properties. In this study, By adding large shot peening particles to original Ti-6Al-4V (TC4) powder, five in-situ shot peening assisted cold sprayed coatings were obtained using nitrogen accelerating gas at different temperatures, and microstructure and the mechanical properties of coatings were evaluated. No phase transformation occurred during the spraying process, and the deposition efficiency was generally more than 60%. The cross-section morphology showed that the coating became denser with the increase in temperature, and the coating showed a structure of alternating dense and porous regions. Local regions struck by large shot-peening particles were denser than other regions. Therefore, the porosity, microhardness, and elastic modulus were divided into two categories. These two categories showed the same trend with temperature: The porosity decreased, whereas the microhardness and elastic modulus gradually increased. The highest values of the latter two properties were 443.4 HV_0.3 (tamped region)/390 HV_0.3 (nontamped region) and 124.8 GPa (tamped region)/110.2 GPa (nontamped region), respectively. Moreover, the bonding and shear strengths increased as the temperature increased, and the fracture morphology showed that brittle fracture was the main type of failure. In addition, by analyzing the microstructure and action depth of shot at different temperatures, it was found that the auxiliary effect of shot peening on the deformation of particles was limited at high gas temperature.