Abstract
Cr3C2–NiCr coatings have been used extensively to combat the erosion corrosion of hydro power turbine blades made of stainless steel. Cr3C2–NiCr coatings are also used in aqueous corrosive environments due to the high corrosion resistance rendered by the NiCr binder. In this investigation, both erosion and corrosion environments are introduced to cermet coating to study corrosion behavior using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The cermet coatings are useful for reducing the risk of deterioration of mechanical properties of hydro power turbines due to the continuous exposure to the erosive and corrosive action of the corrosive environment containing silt. It was observed that Cr3C2–NiCr coating offered a reasonable improvement in corrosion resistance when compared to bare substrate. The corrosion behavior of the coating was studied in a 150 mL solution of 0.1 M NaCl with 2 gms of quartz particles (0.2–0.8 mm) at various rotation speeds (3000, 4500, 6000 rpm) of the solution over a 1 h immersion using potentiodynamic polarization and EIS studies in a specifically designed experimental set-up for erosion corrosion. When compared to the bare stainless steel samples at 3000 rpm and 6000 rpm, the coating showed the highest improvement at 6.57 times and the least improvement at 3.79 times, respectively.
Highlights
In the field of surface engineering, the structural components subjected to dynamic loading and corrosive environments are protected using various coatings such as super alloy coatings, cermets, nanocomposite hard coatings, etc. with superior tribological and corrosion resistance properties.In hydro power turbine industries, accessories such as pumps, impellers and turbine blades are exposed to aggressive conditions, leading to severe erosion-corrosion causing the shut-down of the plants.Slurry erosion, abrasive wear, erosive wear, cavitation erosion and erosion-corrosion are the main glitches in hydro power turbine systems [1,2]
It is further observed that the Icorr value obtained from the potentiodynamic polarization curve the coated sample for 6000 rpm was found to be 3.76 time lower than that obtained for the uncoated resistance of the coating is mainly due to the binding phase of NiCr itself, to less porosity and to there sample for 6000 rpm, which was consistent with the electrochemical impedance spectroscopy (EIS) result showing a 3.79-fold improvement in the being very few microcracks, as well as to the formation of protective post‐corrosion products, such corrosion resistance for the coated sample when compared to the uncoated sample
The electrochemical erosion-corrosion behavior of Cr3 C2 –NiCr coating was investigated in the and the iron oxide layer was observed in the Cr3C2–NiCr‐coated samples after indication of pitting present work
Summary
In the field of surface engineering, the structural components subjected to dynamic loading and corrosive environments are protected using various coatings such as super alloy coatings, cermets, nanocomposite hard coatings, etc. with superior tribological and corrosion resistance properties. Erosion-corrosion is the accelerated degradation of a material or oxide layer on its surface under the combined effect of mechanical erosion and electrochemical attack, whereas erosive wear is caused by the action of sliding, the impact of solids, liquids or gases, or the combination of these To obviate this problem, High Velocity Oxy-Fuel (HVOF) protective coatings are deposited on turbine alloys [4]. Skandan et al revealed that a multimodal powder (combining coarse and fine particles of WC/Co or coating micron-sized aggregates of WC/Co with a readily diffusible binder) did not appear to undergo significant phase decarburization, showing an improved abrasive and sliding wear resistance [14] In such multimodal coatings, the nanocrystalline component is likely to melt with relative ease, leading to high-density coating, with coarse particles having only partially melted [14]. The electrochemical characteristics of the coatings may be correlated with the microstructural morphologies of the degraded coatings to arrive at better protective measures for stainless steel under actual service conditions
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