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Thermal Fracture Resistance of Ceramic Coatings Applied to Metal: I, Elastic Deformation
Author(s) -
LAUCHNER J. H.,
BENNETT D. G.
Publication year - 1959
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1959.tb14083.x
Subject(s) - materials science , thermal shock , composite material , coating , ceramic , thermal expansion , residual stress , fracture (geology) , stress (linguistics) , base metal , philosophy , linguistics , welding
A study was made of the resistance to thermal fracture of four ceramic coatings of the cobalt‐bearing ground‐coat type applied to enameling‐grade iron specimens. The study was made of coated‐metal systems in the unsteady state, symmetrically cooled, and in the absence of viscous or plastic flow. Determinations were made of the elastic characteristics of the coating‐metal composites, the effective coefficient of linear expansion, the temperature at which the coating and base metal were at dimensional equilibrium, and the temperature differential sufficient to induce coating fracture when water quenched. Coating‐metal thickness ratios were correlated with the maximum specimen temperature withstood in water quenching without coating fracture. Studies indicated that ceramic coatings, after receiving a given thermal treatment, fracture when subjected to a thermal shock by a critical temperature differential. When no residual coating stress is present, thermal shock resistance is inversely related to the thermal expansion characteristics of the coating. The critical stress at which coating fracture occurs may be expressed as the sum of thermal and residual stresses developed in annealed systems in which viscous or plastic flow does not occur. Residual compressive stress in a coating is a major factor in improved thermal shock resistance. Increased thermal shock resistance is gained by decreased coating thickness.