A practical approach to fabrication of nano-Al2O3 reinforced MMC coatings by cold spray: Characterization of nanomechanical and tribological performance

Abstract

Cold spray is a crucial solid-state deposition technique involving high-speed spraying of different-sized particles onto a base material. In this study, Ni-based powder reinforced with different proportions of nano-Al2O3 particles was sprayed onto Al6061 alloy by cold spray to improve the coating performance. Nanoparticles are very difficult to deposition as they are affected by the aerodynamic forces generated during cold spraying. With a practical approach, nanoparticles were agglomerated with micron-sized feedstock powders, and nanoparticles in the sprayed powder acted as larger particles and successfully defeated the aerodynamic force. The effects of adding nano-particles on the microstructural, nanomechanical, and tribological properties were investigated. Microstructural analyses revealed that MMC coating layers comprised ceramic particles and metal matrix (Ni and Zn). Due to the high spraying speed, the nano-particles were spread in the relatively ductile matrix formed by Ni and Zn. The micro- and nanohardness values were increased with nanoparticle volume by two mechanisms. In the first mechanism, the hard particle volume increased with the addition of nano powders, and in the second mechanism, the plastic deformation of the matrix increased due to the nano-particles. The sample without nanoparticle reinforcement exhibited plastic deformation during the initial stage of the nanoscratch test. The dry sliding wear test results showed that the nano-Al2O3-reinforced spraying powders increased the wear resistance approximately 1.9 times. According to FESEM and EDS examinations of worn surfaces and WC counter-bodies, nano-particles reduced the transferred layers caused by adhesion to the abrasive counter-body. In addition, the nano-particles were provided a more homogeneous hard particle distribution and improved wear performance.