Microstructure of Cross-Linked High Densification Network and Strengthening Mechanism in Cold-Sprayed Ti-6Al-4V Coating After Heat Treatment

In this study, Ti-6Al-4V (TC4) coating was prepared using an in situ shot peening-assisted cold spraying technology in which large shot peening particles were mixed with TC4 spraying powders to prepare the deposit. To improve its strength and toughness, the coating was heat-treated at 600-1000 °C in vacuum. The results demonstrated that the microstructure of the as-sprayed coating exhibited a special structure that was denser at the regions tamped by the shot peening particles and porous at the nontamped regions. When the coating was heat-treated at 800 and 1000 °C, the interface between the particles had largely disappeared and the local pores had interconnected with each other due to thermal diffusion and recrystallization. The coating hardness decreased slightly after annealing at 600 and 800 °C due to the released strain hardening effect. The bonding strength of the coating after annealing improved in comparison with that of the as-sprayed coating. The tensile strength of the coating improved significantly under annealing at 800 °C. A cross-linked high densification network was formed after annealing due to the effect of in situ shot peening, which served as a reinforced framework and enhanced the strength of the coating.