Crack-Growth Behavior in Thermal Barrier Coatings with Cyclic Thermal Exposure

Abstract

Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs' failure mechanisms. Initial cracks were introduced on the coatings' top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior.

Effect of Deposition Voltage on Layer Thickness, Microstructure, Cu/Ni Sheet Resistivity of Deposition Results by Magnetic Field Electroplating Assisted Technique

“…Third, analyze the microstructure by looking at the peak x-ray intensity data generated through the XRD test. Crystal size ( s g ) determine by the Debye-Scherrer equation that shows in equation (11).…”

“…Fourth, determine the distance between Bragg planes ( d ) through equation (12 Then determine the thickness of the formed Ni layer (  ) using equation (11). The graph of the relationship between the thickness of the nickel layer formed and the deposition voltage shown in Figure 3.…”

“…This is because by increasing the element of Ni on the Cu substrate will increase the amount of Ni crystals formed. By increasing the intensity of nickel diffraction the resistivity of thin film will increase because the higher intensity of diffraction indicates a more orderly arrangement of atoms [11].…”

“…Then the average crystal size is determined from the crystal size for the first and second Ni diffraction peaks. The crystal size for each diffraction peak is determined by equation (11). The relationship of the average Ni crystal size to the deposition voltage is shown in the Figure 7.…”

Effects of Al Sputtering Film on the Oxidation Behavior of NiCrAlY Bondcoat

“…Thermal barrier coatings (TBCs) are widely employed to thermally protect gas turbine engines. The detailed functions of TBCs include the improvement of the efficiency, durability, and properties in high temperature operation environments [1][2][3][4]. TBCs generally comprise three layers, including a ceramic topcoat, an interlayer bondcoat, and a superalloy substrate.…”