Determination of high temperature mechanical properties of thermal barrier coatings by nanoindentation

Abstract

A nanoindentation method is employed to measure the high temperature mechanical properties, including hardness H, Young's modulus E and fracture toughness K c , of 8YSZ (ZrO 2 +8 wt-%Y 2 O 3 ) thermal barrier coatings (TBCs) under as sprayed condition and after subjecting them to thermal oxidation. The tests are conducted on the surfaces of YSZ coatings at temperatures of 250 and 450°C. The expressions for indentation H and E are deduced analytically, and the influence of testing temperature and thermal oxidation on them is discussed. An expression for estimating the fracture toughness of the coatings is also derived. The estimated fracture toughness values for the as sprayed YSZ coatings in terms of stress intensity factor at 250 and 450°C are determined to be 1·58 and 0·84 MPa m 1/2 respectively. For the oxidised YSZ coatings, these values are 1·35 and 1·10 MPa m 1/2 respectively. This study proves that nanoindentation tests can be performed at elevated temperatures for YSZ based TBCs.