Richard Chromik, McGill University, Department of Mining and Materials Engineering, Montreal, QC, Canada
Metal-matrix composites have a long history for use in tribological applications. Hard phase reinforcements can enhance wear resistance and solid lubricant additions can reduce friction. More recently, with maturity of the process, cold spray has become a technology capable of manufacturing metal-matrix composite coatings. In this presentation, research on two coating systems will be described: Al-Al2O3 and Cu-MoS2. In both cases, the addition of the secondary phase provided an enhancement to the tribological performance compared to the pure metal. Mechanistically, these improvements were explained by examination of the flow of “third bodies” – materials generated through the wear process that contribute significantly to the behavior of the tribosystem. In our group, we use an in situ tribometer to directly observe third body formation and flow during tribological testing. Post-analysis of the worn coatings by electron channeling contrast imaging and nanoindentation helped to reveal connections between structural changes and modifications to the mechanical properties induced by wear.
Relationships between the process conditions, structure of the coatings and tribological properties will be discussed. For Al-Al2O3 coatings the role of the volume fraction and morphology of Al2O3 was examined. For the Cu-MoS2 coatings, connections were made from the different steps taken to improve coating deposition to the coating structure and ultimately the tribological performance of the coatings.
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