Effect of WC-10Co on cavitation erosion behaviors of AlCoCrFeNi coatings prepared by HVOF spraying

Abstract

The (AlCoCrFeNi)_1-X(WC-10Co)_X composite coatings were fabricated by HVOF spraying and their microstructures, mechanical properties and cavitation erosion behaviors were tested. The effects of WC-10Co on the cavitation erosion mechanisms were discussed by compared the differences of volume losses and eroded surface morphologies between the coatings. The cavitation erosion resistance of the coatings was about 3 times as that of the 06Cr13Ni5Mo steel. With the addition of WC-10Co, the cavitation erosion resistance of the coating was slightly increased. In the initial stage of cavitation erosion test, the cavitation erosion damage was concentrated on the interface, which was caused by the uncoordinated deformation and poor mechanical properties of the interface between HEA and WC-10Co. When the WC-10Co distributed below the HEA region, the WC-10Co played a strong supporting role and improved the impact resistance of the HEA region. The cavitation erosion mechanism of the HEA1 coating was lamellar spalling. The cavitation erosion mechanisms of the HEA2 and HEA3 coatings were particles spalling and lamellar spalling.

Introduction

In the operation process of the hydraulic machinery, the micro-jets and high-pressure waves caused by the bubble collapse repeatedly hit the surface of flow components, which results in severe cavitation erosion damage and reduces the life of components [[1], [2], [3]]. In order to extend the service life of hydraulic machinery, the high-performance coatings were wildly used to protect the vulnerable parts in industrial production. Some researchers found that the mechanical property played a key role in enhancing the cavitation erosion resistance of the coating [[4], [5], [6]]. Hong et al. [7] prepared WC-10Ni and WC-20Cr₃C₂-7Ni coatings by HVOF spraying and found the WC-20Cr₃C₂-7Ni coating had better cavitation erosion resistance than that of the WC-10Ni coating, which was caused by the superior deformation resistance of the WC-20Cr₃C₂-7Ni coatings. However, the cermet coatings usually have high brittleness and density, which limits their application in hydraulic machinery [[8], [9], [10]]. Therefore, it is necessary to improve the toughness and reduce the density of the coating while ensuring that the coatings can resist the impact of micro-jet. The structural panels for aerospace machinery provide a new approach to design the composite coatings. Some studies found that the sandwich structural panels consisted of high hardness alloy layers and toughened binder had excellent resistance of localized impulsive loading [11,12]. The micro-jets could be equivalent to a localized impact load with high frequency, which is similar to the localized impulsive loading. In addition, the sandwich structural panels have low density, which reduces the weight of aerospace machinery. Therefore, it can be believed that the composite coatings with the sandwich structures of panels may obtain better cavitation erosion resistance.

As we know, the ceramic phase can improve the mechanical properties of the composite coatings [13,14]. Peng et al. [15] used remelt technique of sprayed coating to prepare the FeCoCrNi/WC composite coatings and found that the WC improved the mechanical property and wear resistant of the coatings. In addition, the microstructure of the reinforcement phase can be controlled by changing the preparation technology of the coating, which influence the properties of the coatings. Among the coating preparation technologies, the high-velocity oxygen-fuel (HVOF) spraying technology has the characteristics of high flame velocity and low spray temperature, which results in the superior mechanical properties of the coatings and widely used in machinery industry. Bolelli et al. [16] found that the WC-Co were flattened obviously in Fe-based/(WC–Co)₂₀ composite coatings prepared by HVOF spraying, which was caused by the molten particles impacting on the substrate [[17], [18], [19]]. The wear resistances of the coatings were significantly improved by the addition of lamellar WC-Co. In previous reports, the AlCoCrFeNi coating had higher cavitation erosion resistance than that of 316L steel and showed the great potential of application in composite coatings [20]. Grewal et al. [21] used SiC (10 wt%) to enhance the hardness and fracture toughness of the AlCoCrFeNi coatings, which greatly improved the cavitation erosion resistance of the composite coatings. Although a lot of researches have been done about the influences of the reinforcing phase on the mechanical property of the composite coating, little attention has been paid to the effect of the sandwich structure on the cavitation erosion resistance.

In this study, the AlCoCrFeNi with better plastic deformation property was selected to absorb impact energy and the WC-10Co with higher hardness was used to resist the excessive deformation. In addition, the Co between WC and HEA could lengthen the diffusion path of the carbon, which prevents the carbide formation in the HEA [22]. The (AlCoCrFeNi)_1-X(WC-10Co)_X composite coatings were fabricated by HVOF spraying and their morphologies, phase compositions, mechanical properties and cavitation erosion behaviors were studied. The effects of WC-10Co on the microstructure, mechanical performance and cavitation erosion mechanism of the composite coatings were investigated by compared the differences of volume losses and eroded surface morphologies between the coatings. The experimental data could be used as a reference for the design of the composite coatings applied to hydraulic machinery.