The present work is mainly focused on the investigation of Cr3C2-25NiCr coatings reinforced with 5 % and 10 % of yttria-stabilized zirconia (YSZ) nanoparticles deposited on the CA6NM turbine steel by using the high-velocity oxy-fuel technique. The coatings were analyzed by scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS). The phase identification of a crystalline material was done with the X-ray diffraction (XRD) technique. The SEM/EDS analysis showed that dense and homogeneous coatings were developed by the reinforcement of YSZ nanoparticles. The peaks of XRD graphs of Cr3C2-25NiCr coating reinforced with 5 % and 10 % of YSZ nanoparticles revealed that the chromium and carbon were present as a major phase, and the presence of nickel, yttrium, and zirconium was observed as a minor phase. The porosity level decreased up to 32 % and 45 % by the addition 5 % and 10 % of YSZ nanoparticles as compared with conventional Cr3C2-25NiCr coating. The surface roughness values for coated samples were found to be 5.03, 4.89, and 4.28. The nanocomposite coatings reinforced with 10 % YSZ nanoparticles exhibited the highest microhardness value (1,251 HV). The Cr3C2-25NiCr coatings reinforced with 10 % of YSZ nanoparticles resulted in low porosity, low surface roughness, and high microhardness. During the coating process, the nanoparticles of YSZ flow into the pores and gaps that exist in the coatings and provide a better shield to the substrate material. The Cr3C2-25NiCr with 10 % of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.
The aim of this paper is to investigate the WC-10Co-4Cr coatings reinforced with 5 % and 10 % of yttria-stabilized zirconia (Y2O3/ZrO2; YSZ) nanoparticles deposited on the CA6NM turbine steel by using the high-velocity oxy-fuel (HVOF) thermal spraying technique. In the HVOF technique, the hot jet of the semi-solid particles strikes against the workpiece and creates a layer of coating of varying thickness on the substrate material. The coatings fabricated with HVOF were analyzed by scanning electron microscope (SEM) / energy-dispersive x-ray spectroscopy (EDS). The phase identification of a crystalline material was made with the x-ray diffraction (XRD) technique. The mechanical properties in terms of porosity, surface roughness and microhardness of the nanocomposite coatings were also evaluated. The SEM/EDS analysis showed that dense and homogeneous coatings were developed by the reinforcement of YSZ nanoparticles. The peaks of XRD graphs of WC-10Co-4Cr coating reinforced with 5 and 10 % of YSZ nanoparticles revealed that the WC was present as a major phase and W2C, Co3W3C, Co, Co6W6C, Co6W and Y2O3/ZrO2 nanoparticles were observed as a minor phase. The porosity level decreased up to 42 and 56 % by the addition 5 and 10 % of YSZ nanoparticles as compared with conventional WC-10Co-4Cr coating. The surface roughness values for WC-10Co-4Cr conventional coating, 95 % (WC-10Co-4Cr) + 5 % YSZ and 90 % (WC-10Co-4Cr) + 10 % YSZ nanocomposite coated samples were found to be 5.03, 4.89 and 4.28 respectively. The nanocomposite coatings reinforced with 10 % YSZ nanoparticles exhibited the highest microhardness value (1278 HV). The WC-10Co-4Cr coatings reinforced with 10 % of YSZ nanoparticles resulted in low porosity, low surface roughness and high microhardness. During the coating process, the nanoparticles of YSZ flow into the pores and are dispersed in the gaps between the micrometric WC particles and provide a better shield to the substrate material. The WC-10Co-4Cr with 10 % of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.
Slurry erosion is one of the unavoidable problems in the operation of hydro power stations all over the world. Erosion mainly depends on the surface properties of the hydro turbine material and the different level of operating parameters like impact angle, impact velocity, slurry concentration, particle size and shape. Thermally sprayed hard metal coatings are widely used to protect components and surfaces against erosion wear in various applications. This study focuses on the slurry erosion behaviour of high velocity oxy-fuel (HVOF) sprayed coatings on hydro turbine steel. The HVOF sprayed coatings such as WC-CoCr, Cr3C2-NiCr, Al2O3, stellite, Cr2O3, Cr3C2–NiCr, NiCrSiB–35wt%WC–Co, WC–10Co– 4Cr and WC-12Co results in high bond strength, lower porosity and high resistance to slurry erosion. In this review paper, comprehensive and significant investigation has been made on existing literature of HVOF sprayed coatings on the material of hydro turbine components. The reported research work reveals that the predominant causes of slurry erosion of the uncoated hydro turbine steel include micro-cutting, micropores, cracks, craters, microchipping, pullout, de-bonding and spalling which can be effectively minimize by applying HVOF sprayed coatings.
The aim of the present study is to investigate the slurry erosion behavior of nanoyttria-stabilized zirconia (YSZ) reinforced Cr 3 C 2 -25NiCr ceramic nanocomposite coatings deposited on turbine steel. The Cr 3 C 2 -25NiCr coating powder, 95% (Cr 3 C 2 -25NiCr) + 5% YSZ, and 90% (Cr 3 C 2 -25NiCr) + 10% YSZ nanocomposite coating powder deposited on CA6NM steel samples by using high-velocity oxy-fuel coating technique. L 9 orthogonal array Taguchi method was used to design the experiment. Erosion tests were performed on erosion test rig under hydro accelerated conditions at different levels of various parameters. Erosion tests and analysis of variance resulted that for coated samples, velocity is the major influencing factor followed by slurry concentration, impact angle, and particle size. Velocity was the largest contributor to the mass loss, whereas particle size has the least contribution to mass loss of the coated samples. The scanning electron microscopy analysis of eroded samples revealed that craters, micropores, platelets, plowing, spalling, and so on were responsible for the mass loss of uncoated and coated samples. The incorporation of YSZ nanoparticles decreased the porosity; erodent particles cannot penetrate more deeply inside the workpiece and resulted in less erosion. It has been resulted that 95% (Cr 3 C 2 -25NiCr) + 5% YSZ and 90% (Cr 3 C 2 -25NiCr) + 10% YSZ ceramic nanocomposite coatings exhibited better erosion resistance as compared to Cr 3 C 2 -25NiCr coatings due to high microhardness and low porosity.
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