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

Cold spraying (CS) is a solid-state material deposition process with several unique characteristics, allowing production of coatings or bulk metallic components from a wide range of materials. In this study, a high strength Al alloy AA7055 deposit was prepared by a newly developed in-situ micro-forging assisted cold spray process. In-situ micro-forging effect is introduced during deposition to achieve enhanced inter-particle bonding by mixing large-sized shot-peening particles into the spraying powder. Microstructures of the sprayed deposits were characterized using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Focused Ion beam (FIB) was used to prepare the TEM samples, which allows to characterize the microstructure at the inter-particle interface. Mechanical properties of the sprayed deposit were investigated by tensile tests of the free-standing deposits. By comparing the ultimate tensile strength and elastic modulus of the deposit with the corresponding bulk counterpart, it is found that the in-situ micro-forging 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 mechanisms of enhancing the inter-particle bonding were discussed based on the characterization of the interface microstructure and the distribution of the oxide film at the inter-particle interface.