Passive filler loaded polysilazane‐derived glass/ceramic coating system applied to AISI 441 stainless steel, part 1: Processing and characterization

Abstract

This study describes an oxidation and corrosion resistant environmental barrier coating (EBC) applied to an AISI 441 stainless steel substrate. For this purpose, four polymer-derived ceramic (PDC) coating systems were developed. These coating systems consisted of a bond coat applied by dip coating, and a top-coat that was loaded with passive fillers and deposited by spray coating. The microstructures of the coatings were investigated using optical microscopy and scanning electron microscopy, including energy dispersive spectroscopy (EDS). X-ray powder diffraction (XRD) was used to investigate the phase composition of the coatings. The optimized composite top coatings were prepared from the preceramic polymer HTT1800, filled with yttria-stabilized zirconia and a specially tailored Al 2 O 3 -Y 2 O 3 -ZrO 2 (AYZ) passive filler, and commercial barium silicate glasses were used as sealing agents. After thermal treatment in air at 750°C, uniform and crack-free composite coatings on stainless steel substrates were developed, with thicknesses of up to 93 μm. Oxidation tests, which were performed at 850°C in synthetic air, showed that every tested coating system remained undamaged by oxidation and showed good bonding to the metal substrate. K E Y W O R D Senvironmental barrier coating, high-temperature oxidation, passive filler, polymer-derived ceramics

Passive filler loaded polysilazane‐derived glass/ceramic coating system applied to AISI 441 stainless steel, part 2: Oxidation behavior in synthetic air

“…The process begins with a pretreatment of the steel substrates and the preparation of the coating slurry. The bond coat is then applied via dip coating and fixed by pyrolysis before the composite top coat is spray‐coated and again pyrolyzed in air 30 . The details of the coatings selected for detailed oxidation testing are summarized in Table 1.…”

PDC Glass/Ceramic Coatings Applied to Differently Pretreated AISI441 Stainless Steel Substrates

“…To overcome these unwanted problems, the coatings that consist of only liquid polymer have to be loaded with beneficial components called fillers. The fillers are active [16,17] or passive, and include a large variety of materials, including YSZ [18], Si 3 N 4 [19], Al 2 O 3 [20] and NbC [21] or commercial glasses [22]. The fillers partially or completely compensate the shrinkage, close the pores and increase the coating thickness [23].…”

Oxidation‐Resistant Environmental Barrier Coatings for Mo‐Based Alloys: A Review

“…Moreover, they prevent the formation of defects, as they provide opportunities for a release of gaseous products that have formed during pyrolysis (e.g., N 2 , NH 3 , CH 4 , and O 2 ). [86,89,90] Active fillers are usually based on metals, intermetallics, carbon, or reactive ceramics, such as Si, B, MoSi 2 , or AlN. They fully or partially compensate the shrinkage of the PDC precursor during the polymer-to-ceramic conversion by expansion www.advancedsciencenews.com www.aem-journal.com due to reactions of the filler particles with their environment and the formation of new phases.…”

“…[86] Active fillers serve to provide a stabilizing network of filler reaction products, to increase the ceramic yield, and to provide an inner surface, which is required for material transport during polymer decomposition. [89] The microstructural changes during the polymer-to-ceramic conversion with and without fillers are visualized in Figure 28.…”