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

Abstract

This article features the oxidation behavior of ferritic stainless steel grade AISI 441 coated with protective polymer‐derived ceramics (PDC). Two PDC compositions are studied with respect to their oxidation resistance in a flow‐through atmosphere of synthetic air at temperatures of up to 1000°C. The coatings contain a combination of six passive fillers: Y‐containing ZrO2, glass microspheres, alumina‐yttria‐zirconia (AYZ) powder, and three commercial glasses. They are pyrolyzed in air for 1 hour at 800°C with heating and cooling rates of 3 K/min. Detailed microstructural examination of the oxide products formed at the surface of samples after exposure to air at 900°C, 950°C, and 1000°C for 1‐48 hours is analyzed. Both uncoated steel and steel coated with two of the protective systems described in part 1 of this article are investigated. Fe, Cr2O3, TiO2, and a spinel of the composition (Mn,Cr)3O4 are identified at the oxidized surface of the steel substrate using X‐ray diffraction. A significant weight gain of the unprotected steel is measured after all experiments, while oxidation tests of the coated steel show a negligible weight gain after 900°C and 950°C. During the early stages of coating oxidation, the monoclinic‐to‐tetragonal ratio in the zirconia filler is shifted toward the monoclinic modification. Longer exposures and higher temperatures lead to the formation of yttrium aluminum garnet (YAG) due to glass microsphere crystallization and solid state reactions in the AYZ powder. The crystallization of the three commercial glasses functioning as sealants leads to the formation of Ba(AlSiO4)2 also known as hexacelsian, which subsequently transforms to celsian. YZr8O14 is also formed. The protective effect of the PDC coatings applied to the stainless steel is demonstrated up to 950°C.

High-Temperature Oxidation Resistance of PDC Coatings in Synthetic Air and Water Vapor Atmospheres

“…After oxidation tests, Fe, TiO 2 (PDF-96-900-4143), Cr 2 O 3 (96-901-4037), FeTiO 3 (PDF-96-900-0908), SiO 2 (PDF-96-900-1579), and spinel (Mn,Cr) 3 O 4 (PDF-96-900-5292) were identified from XRD patterns of uncoated steel substrates exposed to synthetic air ( Figure 1 a). These data agree with our previous results, where we performed oxidation tests in an atmosphere of ambient air at temperatures of 900, 950, and 1000 °C [ 32 ]. In this work [ 32 ], stainless steel substrate was covered by the passivation Cr 2 O 3 layer after oxidation, with a TiO 2 and a (Mn,Cr) 3 O 4 spinel non-protective upper layer, while no Fe 2 O 3 was detected by XRD and EDXS.…”

“…The weight gain of steel after oxidation tests increased with increasing temperature. A more detailed study of steel oxidation is described in our previous works [ 30 , 32 ]. Slight weight losses were detected for the C2c and D4 coated steels when tested in synthetic air at 900 °C.…”

“…The oxidation and corrosion resistance of PDC coatings have been studied in several works [ 29 , 30 , 31 ]. In our previous studies [ 32 ], we developed double-layer PDC coatings for steel substrates with thermal stability up to 950 °C using passive fillers. Testing these coatings in an oxidative atmosphere (ambient air) at 1000 °C revealed their unsatisfactory oxidation protection behavior.…”

A Simple Method for a Protective Coating on Stainless Steel against Molten Aluminum Alloy Comprising Polymer-Derived Ceramics, Oxides and Refractory Ceramics

“…Active or passive fillers are, therefore, added to limit shrinkage. In the literature based on oxygen corrosion, the addition of glass in the PDC slurry can be noticed [ 17 , 18 , 19 ]. This glass improves the adhesion of the PDC-containing layer to the substrate and thus improves the corrosion protection of the metal.…”

“…This glass improves the adhesion of the PDC-containing layer to the substrate and thus improves the corrosion protection of the metal. Al 2 O 3 [ 17 ] or Al 2 O 3 -Y 2 O 3 -ZrO 2 [ 18 , 19 ] passive fillers are also blended to minimize the shrinkage and for its good antioxidation properties at high temperature. These, although interesting, composite PDCs have not been evaluated in the presence of molten aluminum.…”