On ultra‐high temperature oxidation of Cr–Cr₃Si alloys: Effect of germanium

Abstract

The oxidation behavior of Cr–Cr3(Si1−XGeX) alloys with the composition range Cr85GeXSi1−X (0 < X < 15) was studied at 1350 °C. Thermogravimetric measurements showed improved oxidation kinetics by alloying up to 2 at% of Ge, but a significant weight loss was observed when higher Ge was added. Phase analysis and composition of the spalled oxide scales and subscale alloy substrates revealed that eskolaite (Cr2O3) forms the protective scale, while SiO2 (cristobalite) is locally formed below the chromia scale. Addition of up to 2 at% altered the morphology of locally formed silica and subsequently affected the spallation of chromia scale. The morphological observations of the different chromia scales are discussed for all alloys oxidized at 1350 °C.

Kinetics of volatilization of high temperature corrosion products and its application to chlorine corrosion

“…This approach can be applied to many other interesting cases of high temperature corrosion dominated by volatile corrosion products despite halogens such as CrO 3 [37,38], CrO 2 (OH) [39][40][41][42], or SiO and Si(OH) 4 [4,5,43] evaporation at very high temperature.…”

Hot corrosion Type II of FeCr‐based model alloys for boiler and heat exchanger applications

“…If the chromium supply by outward diffusion is not sufficient to form or maintain a chromium oxide scale, iron will also be oxidized and the observed multilayered scale will form. The insufficient chromium supply is often believed to originate from local failures of the oxide scale or local depletion of the alloy from the oxide former . The layered iron and chromium oxide scale is observed to be thicker than the pure chromium oxide scale.…”

“…The insufficient chromium supply is often believed to originate from local failures of the oxide scale or local depletion of the alloy from the oxide former. [34,44,45] The layered iron and chromium oxide scale is observed to be thicker than the pure chromium oxide scale. This is attributed to a higher growth rate of this layered scale in comparison to the chromium oxide scale.…”

Oxidation of Cr3Si-Cr7C3/SiC/SiC Coated C/SiC Composite in Wet Air

“…The very low weight loss indicating the consumption of carbon was limited to the subsurface region. At 1300 ºC, enhanced oxidation of the coating led to the rapid closure of the narrow microcracks in the outer layer of the Cr 3 Si-Cr 7 C 3 /SiC/SiC coating due to thermal expansion of the formed SiO 2 and Cr 2 O 3 [25,26]. Moreover, presence of SiO 2 scale was favorable to inhibit the diffusion of both Cr and O, leading to oxidation process slowed and a relative compact oxide scale formed underneath the external oxide scale [27].…”