Design and Fabrication of High-Performance Al-Al2O3 Coatings

In this study, a numerical approach was developed to describe the velocity of in-flight particles and used to help optimize the parameters for cold spraying additive manufacturing of ultra-hard high-strength Al-Al₂O₃ composite coatings. The hardness of the reinforced composite showed isotropy and was improved up to 1.18 GPa for 46 wt.% Al₂O₃ content in the coating This was 4 times higher than that of the Al matrix and among the highest value for an Al-Al₂O₃ composite reported in the literature. The yield strength (σ_0.2%) of the present composite was 317 MPa under compression, which was higher than that of all previously fabricated Al-Al₂O₃ composites prepared by metallurgical methods (less than 250 MPa for powder metallurgy, stir-casting, microwave sintering). The strengthening mechanisms were linked to the Al matrix self-strengthening and the dispersion strengthening from Al-Al₂O₃ particles. For the matrix self-strengthening, high dislocation density (or severe lattice distortion) and low-angle grain boundaries in the Al matrix contributed to reinforcement. For dispersion strengthening, a high Al₂O₃ content in the coating, as well as reduced porosity associated with the consolidation effect of the Al₂O₃ during deposition, led to significant strengthening. Altogether, the design strategy provides a pathway to fabricate high-performance metal-matrix composite coatings.