The mechanism of enhancement of inter-particle bonding in in-situ micro-forging assisted cold spray

Cold spraying (CS) is a solid-state powder deposition process with several unique characteristics, allowing production of coatings or bulk components from a wide range of materials. In this study, AA7055 deposit was prepared by cold spray with commercial AA7055 powder blended with large sized stainless steel particles (in-situ shot-peening particles) using nitrogen gas. The mechanical properties of the sprayed deposits were investigated. The microstructures of the sprayed deposits were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Focused Ion beam (FIB) method was used to prepare the TEM samples, which allows it possible to characterize the microstructure at the inter-particle interface. By comparing the ultimate tensile strength and elastic modulus of the deposits with the corresponding bulks, it is found that the in-situ shot-peening has a positive effect on the bonding of inter-particle. Moreover, by introducing the in-situ hammering effect using shot-peening particles, the plastic deformation of deposited particles is significantly enhanced. The mechanism of enhancing the inter-particle bonding is discussed based on the high resolution characterization of the interface microstructure and the distribution of the oxide film at the inter-particle interfaces.