The thermal expansion of niobium pentoxide and its effect on the spalling of niobium oxidation films

摘要: Abstract The thermal expansion coefficients of stoichiometric and non-stoichiometric niobium, pentoxide have been determined from 20°–1000°C 20°–500°C, respectively, were found to be significantly smaller than that niobium metal. stresses calculated which are induced during cooling a coherent oxide-coated plate. In the absence volume mismatch oxide metal it was concluded due differences in should not cause spalling when oxidized sample is cooled 600°C. A more realistic appraisal, consistent with experimentally observed spalling, made by consideration very large strains arising coherency voluminous on dense surface layers substrate may deform plastically oxidation at high temperatures, even though appreciable contamination strengthening has occurred. Upon cooling, however, added decreasing plasticity contaminated lead crack initiating propagating into brittle oxide.