Microstructure and cavitation erosion resistance of arc ion plating NiCrAlY coating on the 304L stainless steel

In this study, the WC-CoCr coating and Al2O3-TiO2 coating were deposited by high-velocity oxygen-fuel (HVOF) spraying and atmospheric plasma spraying (APS), respectively. Both coatings were immersed in 3.5 wt% NaCl solution with 20 ppm Na2S to investigate their long-term corrosion resistances in the simulated seawater environment. The corrosion behaviors of both coatings for different times were investigated by potentiodynamic polarization, EIS, XRD, EDS and SEM. The electrochemical measurement results showed that the corrosion resistance of both coatings decreased obviously after long-term immersion in sulphide-containing solution, while the Al2O3-TiO2 coating exhibits more stable corrosion performance during the whole immersion process compared with the WC-CoCr coating. The corrosion resistance of the WC-CoCr coating in sulphide-containing solution after long-term immersion was inferior to that of the Al2O3–40TiO2 coating. 

Comparison on long-term corrosion performance of WC-CoCr and Al2O3-TiO2 ceramic coatings in sulphide-containing 3.5 wt% NaCl solution

Improving the hydro-abrasive erosion (HAE) resistance of the existing flow-handling components has been a matter of continuous effort for the hydraulic machineries. In current work, the effects of sand concentrations (SC) and flow velocities (FV) on HAE behaviors of high-velocity oxygen-fuel (HVOF) sprayed carbide-based cermet (i.e. Cr 3 C 2 –NiCr and WC–Cr 3 C 2 –Ni) coatings were studied using a rotating disk rig facility. The obtained results revealed that the WC–Cr 3 C 2 –Ni coating possessed lower porosity value, higher hardness ( H ) and elastic modulus ( E ) values, superior HAE resistances, and appeared less influenced by SC as well as FV compared with the Cr 3 C 2 –NiCr coating. Higher SC and FV caused more severe HAE degradations for both carbide-based cermet coatings, while FV had a greater influence on HAE resistances for both coatings than SC. With the increase of the SC and FV, the Cr 3 C 2 –NiCr coating experienced the HAE process of the isolation of hard phase grains as well as the scouring, the connection of micro-cracks as well as severe plastic deformations, and the crater formation as well as deep scour marks, while the HAE process of the WC–Cr 3 C 2 –Ni coating mainly included the micro-cracks, the erosion pits, and the scour marks. 

Influences of sand concentration and flow velocity on hydro-abrasive erosion behaviors of HVOF sprayed Cr3C2-NiCr and WC-Cr3C2-Ni coatings

Flame-sprayed NiCrBSi/WC-12Co composite coatings were deposited in different ratios on the surface of stainless steel. Oxyacetylene flame remelting treatment was applied to surfaces for refinement of the morphology of the layers and improvement of the coating/substrate adhesion. The performance of the coated specimens to cavitation erosion and electrochemical corrosion was evaluated by an ultrasonic vibratory method and, respectively, by polarization measurements. The microstructure was investigated by means of scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). The obtained results demonstrated that the addition of 15 wt.% WC-12Co to the self-fluxing alloy improves the resistance to cavitation erosion (the terminal erosion rate (Vs) decreased with 15% related to that of the NiCrBSi coating) without influencing the good corrosion resistance in NaCl solution. However, a further increase in WC-Co content led to a deterioration of these coating properties (the Vs has doubled related to that of the NiCrBSi coating). Moreover, the corrosion behavior of the latter composite coating was negatively influenced, a fact confirmed by increased values for the corrosion current density (icorr). Based on the achieved experimental results, one may summarize that NiCrBSi/WC-Co composite coatings are able to increase the life cycle of expensive, high-performance components exposed to severe cavitation conditions.

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Investigations of Cavitation Erosion and Corrosion Behavior of Flame-Sprayed NiCrBSi/WC-12Co Composite Coatings

Research progress of surface modification and solid–liquid lubrication synergistic friction reduction and wear resistance

Components working under harsh environments in power generation, marine, and aerospace sectors are subjected to severe surface degradation because of wear, corrosion, and erosion by solid particles, slurry, silt, and cavitation. Carbide-based materials exhibit high resistance to degradation under such conditions because of their high hardness and chemical stability. These carbides can be effectively deposited as coatings on the components using advanced thermal spray techniques such as plasma spraying, HVOF, and HVAF. The carbide-based thermal spray coatings are majorly based on either WC or Cr3C2 or a combination of these materials. However, the composition of the carbides, the type and percentage of binders, and process parameters significantly affect the performance of these coated components. In this article, the degradation behavior and performance of the different carbide-based coatings as a function of carbide grain size and type of metallic binders, spray process parameters, and working conditions have been critically reviewed. On the other hand, the post-processing of carbide coatings is also emerging as a promising strategy to enhance the performance by modifying and refining the structure of coatings. Hence, a comprehensive summary of the post-processing techniques such as heat treatment, laser treatment, and cryogenic treatment of the carbide coatings is also provided. 

Gurjeet Kaur

Papers

Carbide-based thermal spray coatings: A review on performance characteristics and post-treatment