Abstract
In order to evaluate the interfacial strength between coating film and substrate, a new equation was proposed by expanding the Kendall's equation to the case where the substrate material was in plastic deformation, and the tensile tests were carried out on steel specimens with thermally-sprayed ceramic film and heat-resistant paint film.
When a specimen with partially delaminated film is under tensile load, the interfacial energy between film and substrate, 2γ12 is expressed by the following equation;
2γ12=[P-bB2σys{1-(Ep/Ee)}]2/2b2·B1E1/B2Ep(B1E1+B2Ep)
where P is the load at the beginning of delamination, b is the width of specimen, B1 and B2 are the thickness of film and substrate, E1 is the elastic constant of film, Ee, Ep and σys are the elastic constant, plastic constant, and yield strength of substrate, respectively. The above equation is applicable also for the specimen with smooth film without precrack or partially delaminated portion as long as the cracking of film occurs before the delamination. The interfacial energy of ceramic film obtained by experiment reveals a maximum at a certain film thickness and decreases with an increase in film thickness. The interfacial energy of heat-resistant paint reveals almost the same behavior as the ceramic film, but the film thickness at maximum interfacial energy is much smaller than that of ceramic film.
