THE THERMAL EXPANSION OF NIOBIUM PENTOXIDE AND ITS EFFECT ON THE SPALLING OF NIOBIUM OXIDATION FILMS

Journal Article · Mon Apr 01 04:00:00 EST 1963 · J. Less-Common Metals

DOI:https://doi.org/10.1016/0022-5088(63)90008-0· OSTI ID:4708245

Douglass, D L

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

• Research Organization: General Electric Co., Pleasanton, Calif.
• NSA Number: NSA-17-023883
• OSTI ID: 4708245
• Journal Information: J. Less-Common Metals, Journal Name: J. Less-Common Metals Vol. Vol: 5
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

BRITTLENESS
COOLING
CRACKS
DEFORMATION
DUCTILITY
EXPANSION
FILMS
LAYERS
METALS, CERAMICS, AND OTHER MATERIALS
NIOBIUM
NIOBIUM OXIDES
OXIDATION
OXIDES
SURFACES
TEMPERATURE
THERMAL STRESSES