Key factor governing the deposition of hard phases when cold spraying metallic matrix with mechanically mixed powders

Cold spraying mechanically mixed metal and ceramic powders is a facile strategy for preparing metallic matrix composites. However, in practice, the content of the hard phases in the deposit is usually much lower than that in the raw powder mixture and is still a huge challenge to be higher than 50%. In this work, hard particles including Al2O3, SiC, diamond, WC, and W were used as hard phases, and Al and Cu were used as the metal phase. Mixtures of metallic powders mechanically blended with the hard phases were used as the feedstock. Results indicate that, instead of hardness, the density difference between the hard phase and the metal phase is the key factor determining whether it can be deposited. When pure Al powder was mixed with diamond, SiC, and Al2O3 with similar densities but gradually lower hardness, their contents in the deposits are comparable. However, as pure Al powder was mixed with 50 vol.% of WC powder or W powder for deposition, high hard phase contents of 57.43 vol.% for WC and 78.15 vol.% for W were achieved. Finally, a criterion for effective deposition of hard particles was established based on the ballistic theory.