The reactive element effect on thermally grown chromia scale residual stress

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 343; no. 1; pp. 257 - 264
• Main Authors: Chevalier, S, Valot, C, Bonnet, G, Colson, J.C, Larpin, J.P
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.02.2003; Elsevier
• Subjects: Applied sciences; Corrosion; Corrosion mechanisms; Creep; Exact sciences and technology; Fe–30wt.% Cr alloy; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nd 2O 3 coatings; Oxidation rate; Residual stresses; Spallation; Fe–30wt.% Cr alloy; Spallation; Residual stresses; Creep; Oxidation rate; Nd 2O 3 coatings; Oxide layer; Neodymium oxides; Rupture; Fe-30wt.% Cr alloy; MOCVD coatings; Nd2O3 coatings; Experimental study; Non metal coating; X ray diffraction; Stress relaxation; Chromium alloy; Plasticity; Oxidation; Microstructure; Residual stress; Iron base alloys
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(02)00359-3

Uncoated and Nd 2O 3-coated Fe–30wt.% Cr alloys were oxidized at 1000 °C in air under atmospheric pressure. The oxidation rate was decreased by one order of magnitude when a Nd 2O 3 film was applied to the alloy surface before the oxidation test. X-ray diffraction (XRD) was used to determine residual stresses in chromia scales grown on both uncoated and coated samples. Stresses relaxed by chromia scale spallation from the uncoated alloys. For Nd 2O 3-coated samples, even if stresses were released, no scale spallation was observed. In that case, stresses were supposed to relax by the creep of the chromia scale, owing to the modification of the chromia grain morphology. Indeed, large columnar chromia grains grown on uncoated alloys induced oxide scale failure during cooling to room temperature, whereas small equiaxed chromia grains developed on Nd 2O 3-coated alloys, led to stress relaxation by creep of the scale without cracking. It is assumed that this modification of the chromia-scale plasticity is the main factor to improve the spallation resistance of alloys under thermal shocks.