Abstract
The ability to axially inject liquid feedstock has encouraged the thermal spray research community to explore this concept to deposit coatings for various next generation functional applications. The current study explores the utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings for the first time. The study successfully demonstrates the use of a powder-suspension hybrid processing approach to incorporate a solid lubricant Boron Nitride (as suspension) in a wear resistant Cr3C2–NiCr (as powder) cermet matrix. Coatings were characterized using Scanning Electron Microscopy and Raman Spectroscopy to analyze their microstructure and phase constitution. The results show that the tribological performance of the hexagonal boron nitride (hBN)-incorporated composite coating was significantly better than the traditional powder-derived Cr3C2–NiCr coating. Such hBN-incorporated composite coatings are needed to improve the mechanical properties and enhance the overall tribological performance of metallic components used in various applications, especially at high temperature such as cylinder bore, pistons, deformation tools, etc. The limitations of liquid based lubricants at high temperature motivates the use of hBN reinforced composite coatings as it can form a protective solid lubrication tribo-film. The study concludes that the emerging HVAF technology can accommodate liquid feedstock and be successfully utilized to deposit hybrid powder-suspension composite coatings to create multi length scale microstructures which can be attractive for combining different tribological attributes in the same coatings system.
Highlights
Failure of engineering components subjected to tribological condi tions has been a critical issue for the mechanical industries
Scanning Electron Microscope (SEM) images for all the indents were captured to measure the crack length (c) and the indent half-diagonal length (a)
This can be further confirmed from the 2D plots of the wear track profiles as shown in Fig. 9(c) for both coatings. These results further suggest the presence of the solid lubricant in the composite coating and the formation of a solid lubrication film which is beneficial for the overall wear resistance of the hybrid processed composite coating
Summary
Failure of engineering components subjected to tribological condi tions has been a critical issue for the mechanical industries. Wear-resistant coatings are commonly applied on the surface of the components to tailor the coefficient of friction (CoF) (Motru et al, 2020) and protect the surface from wear (Xiong et al, 2020). (Hoornaert et al, 2010) described in their review paper that over the years, various wear-resistant coating materials (nitrides, carbides, borides, etc.) and their processing routes (chemical vapour deposition (CVD), physical vapour deposition (PVD), thermal spraying, etc.) have been developed. In case of plasma spray (Du et al, 2011) studied the wear performance of NiCr/Cr3C2–NiCr/hexagonal boron nitride (hBN) plasma sprayed composite coating and showed a significant decrease in the friction coefficient due to the presence of hBN whereas (Forn et al, 2003) studied the mechanical and tribological properties of plasma sprayed Al–Si–Mo coatings and found that the increase of Mo content in the coating is beneficial for the mechanical properties
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