Abstract
The processing techniques, microstructural characteristics, and erosion corrosion behaviour of Cr3C2–NiCr and tungsten carbide (WC)-based cermet coatings are reviewed in this work. Conventional and nanocrystalline Cr3C2–NiCr and WC-based cermet coatings are generally synthesized using thermal spray technique. The wear, erosion, and corrosion protection ability of conventional and nanocermet coatings are compared based on available literature. In Cr3C2–NiCr coatings, the corrosion resistance is offered by NiCr metal matrix while the wear resistance is provided by the carbide ceramic phase, making it suitable for erosion–corrosion protection. The nanocrystalline cermet coatings exhibits better erosion–corrosion resistance as compared to the conventional coatings. The nanocrystalline coatings reduces the erosion–corrosion rate significantly compared to conventional coatings. It is attributed to the presence of the protective NiCr metallic binder that allows easier and faster re-passivation when the coating is subjected to wear and the fine-grain structure with homogeneous distribution of the skeleton network of hard carbide phases. In addition, corrosion-accelerated erosion dominates the reaction mechanism of erosion–corrosion and, therefore, higher hardness, strength, and better wear resistance of nanocermet coating along with its faster repassivation kinetics accounts for improved corrosion resistance as compared to conventional coatings.
Highlights
A material is designed according to its specific application and exposure to environment
The super alloys used for high-temperature application such as solar thermal power plants, heat exchangers, gas, and steam turbines suffer from the drawback of poor creep and erosion–corrosion resistance at high temperatures
Cr3 C2 –NiCr coating deposited through thermal spray coating has emerged as one of the best corrosion protective coatings to combat erosion and wear loss of the materials used in hydro power turbines
Summary
A material is designed according to its specific application and exposure to environment. The super alloys used for high-temperature application such as solar thermal power plants, heat exchangers, gas, and steam turbines suffer from the drawback of poor creep and erosion–corrosion resistance at high temperatures To obviate this problem, protective coatings are deposited on super alloys. Cr3 C2 –NiCr coating deposited through thermal spray coating has emerged as one of the best corrosion protective coatings to combat erosion and wear loss of the materials used in hydro power turbines. In this coating, chromium carbide particles are embedded in a NiCr metallic matrix [6]. The present review is focused mainly on conventional and nanocrystalline Cr3 C2 –NiCr and WC-based cermet coatings fabricated by thermal spray technique and their erosion-corrosion behaviors corroborated by detailed investigations reported in the literature so far
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