Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

Abstract

Thermally sprayed cermet coatings are adequate solutions to improve cavitation and wear resistance of hydraulic turbines made of stainless steel (SS), especially in rivers with a high sediment load, such as the Madeira River in Brazil. However, some cermets are easily dissolved in river water, leading to premature failure of the coating and costly maintenance. Moreover, galvanic corrosion induced by coupling the cermet to a SS can accelerate the coating dissolution. Therefore, the corrosion resistance of six cermets (WC-12Co, WC-10Ni, WC-10Co-4Cr, Cr 3 C 2 -25NiCr, Cr 3 C 2 -10NiCr and Cr 3 C 2 -10Ni) and the galvanic corrosion resistance of these materials coupled to CA6NM SS were evaluated in a solution that simulated Madeira River water. WC-12Co and WC-10Ni cermets exhibited the highest corrosion rates, 0.077 and 0.068 mm/ year, respectively, whereas the Cr content in the WC-10Co-4Cr (0.017 mm/year) and Cr 3 C 2 -based coatings (0.005 to 0.007 mm/year) led them to corrode at slower rates. Moreover, the WC-10Co-4Cr and Cr 3 C 2 -based cermets exhibited negligible galvanic corrosion current when coupled to the CA6NM SS, making them good options to coat hydraulic turbines. In contrast, WC-12Co and WC-10Ni coatings underwent a more severe galvanic corrosion process, which would drastically reduce the lifespan of these materials as hydraulic turbine coatings.Keywords corrosion resistance Á Cr 3 C 2 -based coatings Á galvanic corrosion Á power plant Á turbines Á WC-based coatings This article is an invited paper selected from abstracts submitted for the 2020 International Thermal Spray Conference, ITSC2020, that was to be held from June 10-12, 2020, in Vienna, Austria. The conference was canceled due to the coronavirus (COVID-19) pandemic. The paper has been expanded from the planned presentation.

Comparative Analysis of Mechanical Properties of WC-based Cermet Coatings Sprayed by HVOF onto AZ31 Magnesium Alloy Substrates

“…For all samples, at the coatings-substrate interface it could be seen well adhered coating material, which good fi lled substrate surface irregularities. On the crosssection views a good mechanical interlocking with the substrate [34,35]. Such type of structure is a result of the HVOF spraying technology [36].…”

Electrochemical Corrosion Behaviour of Different Grades of WC-Co, High-Cr White Cast Irons and Hadfield Steel in 1 M Sulphuric Acid

“…WC in the WC-Co hardmetals and the Cr-rich primary carbides in the white cast irons. In a study investigating the corrosion behaviour of WC and Cr 3 C 2 -based coatings by Luiz et al [ 53 ], the Cr 3 C 2 -based coatings outperformed the WC-based coatings in resisting corrosive attack. This was seen to also be the case between the two best-performing alloys (WC-12Co and HCWCI-2) investigated in this study.…”

The Effect of Spray Distance on Porosity, Surface Roughness and Microhardness of WC-10Co-4Cr Coatings Deposited by HVOF

“…All coatings are characterized by relatively dense and homogeneous structure. Such type of structure is typical for HVOF coatings [32][33][34][35]. Moreover, the thickness of the deposited coatings was c.a.…”