Property enhancement of cold sprayed Al-diamond MMC coating by using core-shelled diamond reinforcements

Diamond-reinforced metal matrix composites have great potential for wear-resistance applications due to the superior hardness of the diamond component. Cold spray as an emerging coating technique is able to fabricate coatings or bulk materials without exceeding the material melting point, thereby significantly lowering the risk of oxidation, phase transformation, and excessive thermal residual stress. Nickel is well recognized as a wear-resistance metal and always used in high-temperature environment due to its high melting temperature. In this study, thick nickel-diamond composites were produced via cold spray. In order to maximum the diamond fraction in the composites, the core-shell-structured nickel-coated diamond powders were used as the main feedstock. The mixture feedstock of pure nickel and nickel-coated diamond were also used to produce the nickel-diamond composites. Following the fabrication, microstructure characterization and high-temperature tribological test were performed. It was found that, due to its low processing temperature, cold spray is able to prevent graphitization of the diamond in the composites. Further to that, the original diamond phase was almost completely retained in the composites. Finally, the high-temperature wear test showed that the cold sprayed nickel-diamond composites produced in this work had excellent wear-resistance property in high-temperature environment.