Combating Corrosion Degradation of Turbine Materials Using HVOF Sprayed 25% (Cr₃C₂-25(Ni20Cr)) + NiCrAlY Coating

Abstract

High velocity oxy fuel process (HVOF) is an advanced coating process for thermal spraying of coatings on to components used in turbines. HVOF process is a thermal spray coating method and is widely used to apply wear, erosion, and corrosion protective coatings to the components used in industrial turbines. 25% (Cr 3 C 2-25(Ni20Cr)) + NiCrAlY based coatings have been sprayed on to three turbine materials, namely, Ti-31, Superco-605, and MDN-121. Coated and uncoated substrates were subjected to hot corrosion study under cyclic conditions. Each cycle consisted of 1 hour heating at 800 ∘ C followed by 20 minutes air cooling. Gravimetric measurements were done after each cycle and a plot of weight gain as a function of number of cycles is drawn. Parabolic rate constants were estimated for the understanding of corrosion behaviour. It was observed that coated Ti-31 and MDN-121 were more resistant compared to the uncoated ones. Uncoated superco-605 was undergoing sputtering during corrosion study and hence comparison between coated and uncoated superco-605 was difficult. The cross-sectional analysis of the corroded, coated samples indicated the presence of a thin layer of chromium oxide scale on the top of the coating and it imparted better corrosion resistance. Parabolic rate constants also indicated that coating is more beneficial to Ti-31 than to MDN-121.

Cavitation erosion and sliding wear resistance of HVOF coatings

“…The oxidation and decarburization processes are unavoidable during thermal spraying, which is confirmed by the results of chemical analysis of coatings after spraying, contained in Table I and Figure 1. Oxygen has been identified on the surface of the coatings, which is consistent with the literature data [1] presented for Cr3C2-NiCr coatings produced by HVOF, moreover, oxidation of the coating material can lead to decarburization of Cr3C2 carbide and formation of Cr7C3 carbides [11]. In the case of coatings of the MCrAlY type, the forming aluminum oxides have a positive effect, because they provide thermal and chemical resistance of the coating [7].…”

“…According to the literature data [8,11,21], cermetal coatings of Cr 3C2-NiCr type produced by the HVOF method may contain Cr3C2, Cr7C3, Cr2O3 and phases made of chromium and nickel, the matrix may contain amorphous phases and nanocrystalline metal grains. The hardness of Cr3C2-NiCr coatings is in the range of 850÷1150 HV [1,6,11]. The oxidation and decarburization processes are unavoidable during thermal spraying, which is confirmed by the results of chemical analysis of coatings after spraying, contained in Table I and Figure 1.…”

Experimental Investigation on the Effect of Coating Al2O3+70% NiCrBSi Cermets on Ti‐31 Superalloy to Combat Hot Corrosion

“…The cermets is a composite material made up of ceramic (cer) and metal (met) elements; cermets can combine the attractive features of both a ceramic and a metal, such as high-temperature resistance and hardness [6][7][8]. Coating of cermets on the superalloys can certainly be beneficial in enhancing the life of operation of the components made of superalloys [9][10][11]. HVOF technique is the most popularly used thermal spray coating technique of deposition of cermets onto the substrates, as it is proved to provide a coating with properties like good bond strength between substrate and coating, less porosity, and laminar structured coating [12][13][14].…”

Cavitation Erosion and Sliding Wear of MCrAlY and NiCrMo Coatings Deposited by HVOF Thermal Spraying

“…Moreover, according to the literature [10][11][12], the abrasive wear and particularly sliding wear are dominant processes of materials degradation. Furthermore, erosion by solid particles and corrosion is frequently described damage processes in literature [13][14][15][16][17].…”