Investigating the effect of heat treatment on microstructure and mechanical and tribological behavior of Co-Cr-Mo-Si alloy thermal spray coatings depending on alloy composition

Date

2024-6-10

Author

Ertürk, Murat Tolga

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Effect of alloy composition with variable Cr content on the general microstructure, mechanical properties and wear performance of CoMoCrSi coatings before and after 900°C annealing heat treatment were studied comparatively. Increase in Cr percent in the alloy had the effect of a parallel increase in the inter-splat boundary volume, which proved detrimental to the physical integrity of the coating against forces in as-coated state. Annealing the coating resulted cohesion of the inter-splat boundaries, crystallization of the structure and formation of grain boundaries resulting an increase of hardness and inter-splat bonding strength of respectively 15-50% and 4-6 times. While, as-coated specimens showed gradually increasing wear losses parallel to the Cr content; annealed specimens performed significantly better at room temperature, yielding lower results independent of alloy composition. Moreover, at 600°C, as-coated and annealed specimens both had low wear losses having similar results with room temperature tests of as-coated specimens. Oxide layers constituted by various oxides of Co, Mo and Cr were formed on the surface of specimens tested at high temperature, which accounted for increased integrity, hardness and wear performance for especially the specimens in as-coated state. Consequently, inter-splat boundary structure was found to be the dominant character for performance of the coatings especially in room temperature conditions. Annealing or high temperature applications accounted to be factors potentially eliminating any vulnerability of the coating arising from the bonding characteristics considering the general physical and tribological performance.

Subject Keywords

Thermal spray, CoCrMoSi, Heat treatment, Alloy composition

URI

https://hdl.handle.net/11511/110103

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Graduate School of Natural and Applied Sciences, Thesis