In Situ Measurement of the Toughness of the Interface Between a Thermal Barrier Coating and a Ni Alloy

Abstract

A flexural test for the in situ measurement of the delamination toughness of the interface between a thermally grown oxide and a bond coat in the presence of a thermal barrier coating (TBC) has been implemented. To accomplish the testing, a section of the substrate was removed by microelectro-discharge machining and a precrack introduced through the TBC by center point loading. This was followed by application of an asymmetric single-point load to extend a delamination along the interface. A displacement and strain mapping method was used to locate the delamination and to ascertain its extension. To relate the energy release rate and mode mixity to the crack extension and the loads, a finite-element method was implemented. The ensuing fracture resistance was found to vary along the interface with values in the range of 25-95 J/m 2 .

Lifetime Assessment for Thermal Barrier Coatings: Tests for Measuring Mixed Mode Delamination Toughness

“…Jones et al 11 sliced a planar section of a electron beam deposited TBC system on a turbine blade substrate. Then these authors used a focused ion beam to cut a broad notch under the coating system creating a trilayer bridge consisting of the bond coat, the TGO and the topcoat.…”

Room temperature plasticity in thermally grown sub-micron oxide scales revealed by micro-cantilever bending

“…Conventional indirect measurements of oxide scale behavior have traditionally been limited to thicker oxide scales, often in the range 5-50 µm, in which the probability of defect occurrence is high. More recently, test methods using bi-layer beams extracted from macroscopic specimens have been used to measure in-plane elastic properties [11] and delamination toughness [12] of thermal barrier coatings. With the advancement of technologies such as focused ion beam (FIB) milling and micro-mechanical testing methods, the use of direct tests at the micro-to nano-scale, such as micropillar compression, has become possible [13][14][15].…”

Influence of isothermal and cyclic oxidation on the apparent interfacial toughness in thermal barrier coating systems

“…The resistance to spallation is intimately related to the capacity of interfaces of the complex TBC system to sustain crack initiation and propagation, which can be evaluated by measuring the interfacial toughness. Several methods have been proposed to achieve interfacial fracture toughness measurement for various substrate/coating systems, including "four point bending test" [3], "barb test" [4], "buckling test" [5], "micro-bending test" [6] and various indentation techniques [7][8][9][10][11]. This paper proposes to implement the Vickers hardness technique to estimate the interfacial toughness in EB-PVD TBCs as well as its evolution upon various isothermal and cyclic aging conditions.…”