Effects of Heat Exposure Time and Temperature on the Delamination Behavior of Air Plasma-Sprayed Thermal Barrier Coatings under Shear Loading

Abstract

The delamination behavior of air plasma-sprayed thermal barrier coatings (APS-TBCs) exposed to heat in air at different temperatures was evaluated under mode II loading conditions. The TBC layer, BC layer, and substrate were composed of 8 mass% Y 2 O 3 partially stabilized ZrO 2 , NiCoCrAlY alloy, and Inconel 738 nickel base superalloy. The heat exposure was performed at 1173 K or 1423 K for 10 to 200 h. During the heat exposure, the thickness of thermally grown oxide (TGO) increased and the hardness of the bond coat (BC) layer near the TGO decreased with increasing heat exposure time. The delamination toughness decreased monotonically with increasing heat exposure time when the TBCs were heat exposed at 1173 K. In this case, delamination occurred at the TBC layer. The average thickness of the remaining TBC on the substrate side decreased with increasing exposure time. As for the TBCs exposed at 1423 K, the delamination toughness increased over the rst 50 h, but then began to decrease with further exposure time. The delamination pathway has transferred to near the TGO layer. The fraction of TBC layer fracture decreased, whereas those of the TBC/TGO interface and TGO/BC interface fracture increased with increasing exposure time. The change in delamination toughness may have been caused by the interaction between the TGO thickening and the reduction of BC layer hardness. The increase in TGO thickness decreased the delamination toughness due to an increase in residual stresses. The decrease in hardness of the BC layer near the TGO may have increased the delamination toughness by increasing the plastic dissipation.

Microstructural Change and Fracture Behavior under Different Heat Exposure Conditions on Thermal Barrier Coatings Deposited on TiAl Intermetallic Compound

“…When the TBCs was heat exposed at 1073 K and 1173 K, shear strength tends to decrease with increasing heat exposure time after showing the maximum shear strength with 10 h heat exposure. This tendency is similar for TBCs using nickel base superalloy as substrate [6,8]. The increase in shear strength, which relates to the delamination toughness [6][7][8] was probably an effect of plastic dissipation due to the decrease in yield stress of the BC layer by heat exposure.…”

“…This tendency is similar for TBCs using nickel base superalloy as substrate [6,8]. The increase in shear strength, which relates to the delamination toughness [6][7][8] was probably an effect of plastic dissipation due to the decrease in yield stress of the BC layer by heat exposure. The decrease in shear strength might be due to the increase in the residual stress of the TBCs by the formation and growth of the TGO layer.…”

“…Change of chemical composition in each layer is measured by energy dispersive X-ray analysis and electron probe micro analysis. In order to understand the delamination behavior under shear loading, shear strength of the TBCs is measured by pushout test method [6,7]. After the tests, fracture surfaces were observed.…”

Research Progress of Failure Mechanism of Thermal Barrier Coatings at High Temperature via Finite Element Method

“…The structure and mechanical properties of functionally graded coatings are continuous, with the composition of the coatings due to the gradient change between the ceramic layer and the metallic substrate. This continuous structure can effectively alleviate the thermal stress between the ceramic layer and the metallic substrate, and effectively improve the thermal shock resistance of the coating [24]. Functionally graded TBCs have excellent thermal shock resistance compared with double-layer TBCs, but the preparation is difficult and the repeatability limits the practical application of functionally graded TBCs.…”

Comparison of Microstructure and Tribological Properties of Plasma, High Velocity Oxy-Fuel and Detonation Sprayed Coatings from an Iron-Based Powder

“…The particle molten and spread state are mainly influenced by spray temperature, particle collision speed 26) and base material temperature. 27) It's generally known that the plasma spray temperature is between 6000°C³10000°C, 8) HVOF spray temperature is about 2800°C, 28) detonation spray temperature is about 3000°C. 29) The melting point of Fe-based alloy powder is below 2000°C.…”