Laser Clad and HVOF-Sprayed Stellite 6 Coating in Chlorine-Rich Environment with KCl at 700 °C

Abstract

Laser clads and HVOF coatings from a stellite 6 alloy (Co-Cr-W-C alloy) on 304 stainless steel substrates were exposed both bare and with KCl deposits in 500 ppm HCl with 5% O 2 for 250 h at 700°C. SEM/EDX and PXRD analyses with Rietveld refinement were used for assessment of the attack and for analysis of the scales. The bare samples suffered from scale spallation and the scale was mostly composed of Cr 2 O 3 , CoCr 2 O 4 and CoO, although due to dilution haematite (Fe 2 O 3 ) was detected in the scale formed on the laser clad sample. A small amount of hydrated HCl was detected in bare samples. While the corrosion of the bare surfaces was limited to comparatively shallow depths and manifested by g and M 7 C 3 carbide formation, the presence of KCl on the surface led to severe Cr depletion from the HVOF coating (to 1 wt%). Both inward and outward diffusion of elements occurred in the HVOF coating resulting in Kirdendall voids at the coatingsteel interface. The laser clad sample performed significantly better in conditions of the KCl-deposit-induced corrosion. In addition to the oxides, CoCl 2 was detected in the HVOF sample and K 3 CrO 4 was detected in the laser clad sample. Thermodynamic calculations and kinetic simulations were carried out to interpret the oxidation and diffusion behaviours of coatings.

Preparation of MCrAlY–Al2O3 Composite Coatings with Enhanced Oxidation Resistance through a Novel Powder Manufacturing Process

“…Thermodynamic calculation of oxidation products as a function of effective partial pressures of O 2 at 900°C was carried out by Thermo-Calc Ò software (Version 2017b) with TCS Ni-based superalloys (TCNi8.1) database following CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) ( Ref 27,28). The use of Thermo-Calc Ò on alumina-forming and chromia-forming alloys systems has been validated by our previous work (Ref 29,30) and others (Ref [31][32][33][34][35][36][37][38].…”

Experimental and thermodynamic investigations on the chlorine-induced corrosion of HVOF thermal sprayed NiAl coatings and 304 stainless steels at 700 °C

“…The flow rates of kerosene and oxygen were 415 mL/min and 800 L/min, respectively; nitrogen was used a carrier gas for the powder. The dimensions of the samples for the corrosion tests were 10 mm × 10 mm, same with our previous studies [28,29]. It is worth noting that since the samples were not fully coated with NiAl coatings, the sample edges may act as an initiation for the corrosion attack.…”

“…Thermo-Calc ® calculation is a useful tool to study the selective oxidation behaviour of alloys, especially those complex multicomponent alloys [37]. The application of Thermo-Calc ® to provide insight into the alumina-forming and chromia-forming alloys systems has been validated by our previous work [28] and others [38][39][40][41][42][43][44][45]. All calculations were based on fixed concentrations, pressures and temperatures, so as to match the isothermal corrosion test used in the present study.…”

Microstructure and Electrochemical Corrosion Behaviors of Laser‐Cladded 2205 Duplex Stainless Steel

“…Compared with spray coating, electroplating, and vapor deposition, laser cladding requires a low dilution and produces a fine microstructure and good adhesion to the substrate. Therefore, it is widely used in the aerospace, mould, and electrical industries …”