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 z8 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 450uC. 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 450uC 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.
Coated nonmagnetic conductors are subject to material degradation hidden under nonmetallic coating. It is formidable to evaluate the degradation degree and thickness of degradation region without removing the non-conductive coating. In light of this, in this paper the feasibility of pulsed eddy current (PEC) probes for nondestructive assessment of hidden material degradation in coated nonmagnetic conductors was investigated. The characteristics of lift-off intersection (LOI) of signals from PEC probes were utilized in a bid to cancel out the influence of coating thickness on signals. A fast inverse scheme based on LOI was proposed, along with the probe to implement simultaneous evaluation of the degradation degree and thickness. A series of experiments revealed that the proposed probe is high-efficiency and capable of assessing hidden material degradation without much loss of accuracy.
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