Tensile Test Specimens with a Circumferential Precrack for Evaluation of Interfacial Toughness of Thermal-Sprayed Coatings

• Published in: Journal of thermal spray technology 2008-06, Vol.17 (2), p.228-233
• Main Authors: Kishi, Akio, Kuroda, Seiji, Inoue, Tadanobu, Fukushima, Takeshi, Yumoto, Hisami
• Format: Article
• Language: English
• Subjects: Adhesion; Adhesion tests; Analytical Chemistry; Applied sciences; Carbon; Characterization and Evaluation of Materials; Chemistry and Materials Science; Circumferences; Coatings; Corrosion and Coatings; Exact sciences and technology; Flat surfaces; Fracture toughness; Fractures; INT; Machines; Manufacturing; Materials Science; Mathematical analysis; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Peer Reviewed; Processes; Production techniques; Surface treatment; Surfaces and Interfaces; Thin Films; Tribology
• ISSN: 1059-9630; 1544-1016
• DOI: 10.1007/s11666-008-9168-2

A new testing procedure to evaluate the interfacial toughness of thermal-sprayed coatings has been developed. The newly designed test specimen is a modification of the pin test with an artificially introduced weak interface, which is expected to open up easily under tensile loading and act as a circumferential precrack along the interface between a coating and the substrate. This configuration makes it possible to calculate the stress intensity factor K Int at the tip of the precrack, which can be expressed as , where σ 0 is the apparent average stress, a the crack length, R the specimen radius, and F I the geometrical correction function. Finite-element analysis was carried out to calculate the correction function F I for various values of a / R. In the experiments, the flat surface of a pin was grit-blasted and a ring-shaped area from the periphery was covered with carbon using a pencil and set into a mating dice. SUS316L stainless steel was plasma-sprayed onto the flat surface of the pin and the dice. Then, tensile load was applied to the pin to break the weak interface containing the carbon and finally the unmodified coating-substrate interface. The load required to pull out the pin was measured for various specimen parameters such as a and R . The results indicate that the adhesion of the tested coatings can be represented by interface toughness of 1.9 ± 0.1 MPa m 1/2 . As a consequence, this testing procedure can be considered as a viable method to evaluate adhesion of a thermal-sprayed coating on a substrate.