Abstract
Metallic coatings based on cobalt and nickel are promising for elongating the life span of machine components operated in harsh environments. However, reports regarding the ambient temperature tribological performance and cavitation erosion resistance of popular MCrAlY (where M = Co, Ni or Co/Ni) and NiCrMoNbTa coatings are scant. This study comparatively investigates the effects of microstructure and hardness of HVOF deposited CoNiCrAlY, NiCoCrAlY and NiCrMoNbTa coatings on tribological and cavitation erosion performance. The cavitation erosion test was conducted using the vibratory method following the ASTM G32 standard. The tribological examination was done using a ball-on-disc tribometer. Analysis of the chemical composition, microstructure, phase composition and hardness reveal the dry sliding wear and cavitation erosion mechanisms. Coatings present increasing resistance to both sliding wear and cavitation erosion in the following order: NiCoCrAlY < CoNiCrAlY < NiCrMoNbTa. The tribological behaviour of coatings relies on abrasive grooving and oxidation of the wear products. In the case of NiCrMoNbTa coatings, abrasion is followed by the severe adhesive smearing of oxidised wear products which end in the lowest coefficient of friction and wear rate. Cavitation erosion is initiated at microstructure discontinuities and ends with severe surface pitting. CoNiCrAlY and NiCoCrAlY coatings present semi brittle behavior, whereas NiCrMoNbTa presents ductile mode and lesser surface pitting, which improves its anti-cavitation performance. The differences in microstructure of investigated coatings affect the wear and cavitation erosion performance more than the hardness itself.
Highlights
Published: 23 December 2021Thermal spraying processes are commonly used methods for metallic materials restoration and modification of surface layer properties that are applied in many industries
The HVOF method is most often used because the process is characterized by a high particle velocity, relatively low temperature and a short time of particle exposure in the stream, which results in a low content of oxides and minimal porosity [4,5]
Much more uniform surface roughness was identified for NiCrMoNbTa than for MCrAlY’s (Figure 4)
Summary
Published: 23 December 2021Thermal spraying processes are commonly used methods for metallic materials restoration and modification of surface layer properties that are applied in many industries. In comparison to other thermal spraying techniques such as arc, flame spraying, or APS coatings deposited using the HVOF, they are usually characterized by high adhesion to the substrate and low porosity [6,7,8,9]. This technology allows for the extension of the service life of materials, the improving of the mechanical properties, and the increase in the operational performance of the engineering devices. Systematic broadening of the coatings industrial applications followed by the diversity of the feedstock materials makes the thermally sprayed coatings a crucial subject of recent scientific papers
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