Key Factors Governing the Deposition of Hard Phases when Cold Spraying Metallic Matrix with Mechanically Mixed Powders

Cold spraying ductile metal and hard-phase powder blends is a facile strategy for additive manufacturing of the metallic matrix composites. However, in practice, the hard particle content in the composite is always lower than in the powder blends and difficult to exceed 40 vol.% no matter how much in the feedstock blends and what kind spraying parameters are selected, and the underlying mechanisms remain unclear. The present work shows that instead of hardness and elastic modulus, the density ratio of the hard phase to the metal phase is the key factor determining successful deposition of the hard particles. When 50 vol.% of SiC powder or diamond particles are mixed into Al, only 23.9 vol.% of SiC and 26.0 vol.% of diamond are deposited. However, when Al powder is mixed with 50 vol.% of high-density WC powder or W powder, high hard-phase contents of 57.9 vol.% for WC and 79.8 vol.% for W are detected in the deposits, breaking the record for hard-phase content in cold-sprayed composites. Moreover, a universal criterion for the effective deposition of hard-phase particles is established and strategies to improve the hard-phase content in the cold-sprayed composites are proposed.