Film Thickness Dependency of Interfacial Strength Evaluation for Thin Film Coating Structure by Nanoindentation Method

概要

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Nanoindentation tests were conducted for polyimide (PI) coating / Si substrate specimens and the energy release rates were evaluated as the interfacial strength. The energy release rate due to coating delamination was obtained from the load-displacement curve by the method proposed by Omiya et al. Three specimens that have different thickness and another kind of specimen which is the same as the thinnest coating but with an additional layer were prepared. The dependencies on the coating thickness and delamination propagation rate were investigated. The interfacial strength of the only thinnest coating case is underestimated, since small scale yielding conditions were not satisfied. The value of the interfacial strength between PI coating and Si substrate increases with increasing of the delamination propagation rate. The value becomes constant when the delamination propagation rate exceeds around 7.0×10-3 mm/s. By considering the unloading curve, the corrected evaluation method for interfacial strength was proposed. The interfacial strength evaluated by the corrected method converge for all specimens cases.