Hot Corrosion Resistance of Laser-Sealed Thermal-Sprayed Cermet Coatings

Abstract

Hot corrosion affects the components of diesel engines and gas turbines working at high temperatures, in the presence of low-melting salts and oxides, such as sodium sulfate and vanadium oxide. Thermal-sprayed coatings of nickel-chromium-based alloys reinforced with ceramic phases, can improve the hot corrosion and erosion resistance of exposed metals, and a sealing thermal, post-treatment can prove effective in reducing the permeability of aggressive species. In this study, the effect of purposely-optimized high-power diode laser reprocessing on the microstructure and type II hot corrosion resistance of cermet coatings of various compositions was investigated. Three different coatings were produced by high velocity oxy-fuel and was tested in the presence of a mixture of Na 2 SO 4 and V 2 O 5 at 700 • C, for up to 200 h: (i) Cr 3 C 2 -25% NiCr, (ii) Cr 3 C 2 -25% CoNiCrAlY, and (iii) mullite nano-silica-60% NiCr. Results evidenced that laser sealing was not effective in modifying the mechanism, on the basis of the hot corrosion degradation but could provide a substantial increase of the surface hardness and a significant decrease of the overall coating material consumption rate (coating recession), induced by the high temperature corrosive attack.

Influence of Ultrasonic Excitation Sealing on the Corrosion Resistance of HVOF-Sprayed Nanostructured WC-CoCr Coatings under Different Corrosive Environments

“…Cermets are a new class of ceramic materials with a relevant scientific and applicative interest as they have a favorable combination of high-temperature stability, exceptional mechanical properties, tolerance to damage under cyclic loadings, and high wear and corrosion resistance in different environments. The anti-corrosion properties of cermets depend upon chemical composition and microstructure, which are the most influential parameters [9][10][11][12]. Thermal spraying technologies are widely adopted industrially to deposit different kinds of coatings (i.e., metallic, intermetallic, ceramic, and cermet) for protecting substrate, which is exposed to extremely difficult operating conditions related with high temperatures, aggressive environments, and mechanical load [13].…”

Special Issue: “Coatings for Harsh Environments”

“…In addition to ceramic thermal barrier coatings, cermet coatings are also being developed to endure hot corrosion. These coatings when sealed by a high-energy laser offer better corrosion resistance than unsealed coatings [5].…”