tailieunhanh - Substrate and Coating Erosion_8

Tham khảo tài liệu 'substrate and coating erosion_8', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 230 5 Substrate and Coating Erosion Fig. Debonding of a polymer layer from a metal substrate adapted from Engel and Pedroza 1983 . a Blunt spherical indenter b Sharp conical indenter level. A large normal compressive stress is exerted through the polymer film which is dragged into the contact zone. Ritter and Rosenfeld 1990 distinguished three basic types of debonding shown schematically in Fig. . Type I occurs when the deformations in the coating remain elastic up to debonding. In type II the coating deformations underneath the indenter are predominantly plastic at debonding but the substrate is not penetrated. Type III occurs when the indenter has penetrated the coating before debonding occurs so that part of the indentation load is supported directly by the substrate. The failure type for a given system coating substrate will depend on the properties of the coating coating thickness adhesion strength and indenter geometry. Blunt indenters and thick poorly adhering coatings favour type I whereas sharp indenters and thin well-adhering coatings favour the types II and III Ritter and Rosenfeld 1990 . Plastic deformations of the substrate metal tend to cause pile-up around the rim of the crater and further out along the surface a tensile load between film and substrate arises. Separation between coating and steel substrate occurs for the following condition Debonding of Organic Coatings 231 ƠT ƠB The polymer film departed from the substrate along the rim of the indented crater but it rejoined the substrate beyond an annulus of debonded space where the tensile stress was insufficient to prevent anchorage. For very sharp indenters a hole on the bottom of the indentation could be observed frequently Engel and Pedroza 1983 . Indentation radius a in Fig. as well as debonding radius b in Fig. had almost linear relationships to the indentation force in the range between 2 and 27 N. Examples are shown in Fig. . Engel 1985 considered the .