Processing map of the in-situ micro-forging (MF) assisted cold spray for additive manufacturing of fully dense metals without MF particle inclusion

The newly developed in-situ micro-forging assisted cold spraying (MFCS) is an economical and convenient way to deposit dense metals with porosity lower than 0.1 %. During this process, forging effect induced by impact of large-size hard micro-forging particles to in-situ densification of the deposited materials. Therefore, a fully dense metallic deposit could be produced at moderate gas temperature and pressure without using expensive helium gas. However, it is found that the porosity is highly dependent on the type of depositing materials, shot-penning particle size, and spraying parameters. Shot-peening particle deposition-induced inclusion is frequently observed for soft depositing materials. This makes the application challenging and a universal processing map is in great demand. In this study, pure Al, pure Ti, pure Ni, 2219 Al, 6061 Al, 7055 Al, and TC4 with different hardness values are used as examples to explore a universal spraying processing map for MFCS. The influence of impact velocity and volume fraction of the shot-peening particle, types of the depositing materials, and spraying parameter on densification and shot-peening particle deposition is investigated. Adding 30 vol. % of 410 stainless steel MF particles into the depositing powders decreases the porosity of all deposits and particle deposition-induced inclusion is observed in pure Al, all three Al alloys, and pure Ti deposits. The single particle deposition experiment and the numerical simulation reveal that mechanical interlocking is the prime mechanism for MF particle deposition. A critical embedding MF particle size (dcr,e), above which MF particle inclusion can be avoided, is defined. A new concept of MF intensity (IMF) is proposed to comprehensively consider all main factors influencing the densification of the deposit. Finally, optimized processing maps for depositing fully dense metals without MF particle inclusion are established by plotting the critical embedding velocity and IMF against the hardness of the depositing materials.