Strength and toughness measurement of thin brittle coatings on substrates Part II. Experimental determination

Abstract A method is demonstrated to measure the ultimate tensile strength, fracture toughness, Weibull modulus and surface energy of micron-sized ceramic coatings on substrates. The properties of chemically vapor-deposited coatings of Al 2 O 3 , Al 2 O 3 + ZrO 2 and TiN were measured on SiC, Si 3 N 4 and WC-6Co substrates. The fracture stresses of these coatings are 190–2200 MPa, the fracture toughnesses are 0.4-3.8 MPa m 1 2 , the Weibull moduli are 10–29, and the surface energies are 0.3–13 J m −2 . This work has shown that the tensile strength of thin brittle coatings can be significantly higher than bulk values and the fracture toughness of a coating can be significantly lower than bulk values.