Isothermal oxidation and TGO growth behaviors of YAG/YSZ double-ceramic-layer thermal barrier coatings

This study places great emphasis on the relationship between the TGO chemical composition and the TGO growth rate and the mechanical property of thermal barrier coatings upon isothermal oxidation. The results indicate that the control of the θ-Al2O3α-Al2O3 phase transformation can have significant effects on the subsequent isothermal oxidation during the earlier stage of isothermal oxidation. The formation of (Al, Cr)2O3 oxide sub-layer originated from the textured and larger grain of α-Al2O3 can influence the potential TBCs lifetime. Additionally, the potential longer oxidation lifetime of TBCs that subjected to the appropriate vacuum heat pre-treatment can be attributed to the larger absorptive energy of the TGO area prior to its fully microcrack imperfection propagation. Most importantly, TBCs delamination was determined by the steady-state energy release rate in ceramic topcoat and TGO, the TGO and the interface, as well as the formation and development of the microstructure and composition of imperfections in the vicinity of the interface.

Download Full-text

Understanding the Failure Mechanism of Thermal Barrier Coatings Considering the Local Bulge at the Interface between YSZ Ceramic and Bond Layer

Materials ◽

10.3390/ma15010275 ◽

2021 ◽

Vol 15 (1) ◽

pp. 275

Author(s):

Zhi-Yuan Wei ◽

Hong-Neng Cai

Keyword(s):

Crack Propagation ◽

Thermal Barrier Coatings ◽

Local Stress ◽

Ceramic Layer ◽

Thermal Barrier ◽

Interface Morphology ◽

Barrier Coatings ◽

Coating Failure ◽

Bond Layer ◽

Tgo Growth

The TC/BC interface morphology in APS TBC is one of the important factors leading to crack propagation and coating failure. Long cracks are found near the bulge on the TC/BC interface. In this study, the TBC model with the bulge on the interface is developed to explore the influence of the bulge on the coating failure. Dynamic TGO growth and crack propagation are considered in the model. The effects of the bulge on the stress state and crack propagation in the ceramic layer are examined. Moreover, the effects of the distribution and number of bulges are also investigated. The results show that the bulge on the interface results in the redistribution of local stress. The early cracking of the ceramic layer occurs near the top of the bulge. One bulge near the peak or valley of the interface leads to a coating life reduction of about 75% compared with that without a bulge. The increase in the number of bulges further decreases the coating life, which is independent of the bulge location. The results in this work indicate that a smooth TC/BC interface obtained by some possible surface treatments may be an optional scenario for improving coating life.

Download Full-text

NONDESTRUCTIVE IMPEDANCE SPECTROSCOPY EVALUATION OF THE BOND COAT OXIDATION IN THERMAL BARRIER COATINGS

Surface Review and Letters ◽

10.1142/s0218625x07010494 ◽

2007 ◽

Vol 14 (05) ◽

pp. 935-943 ◽

Cited By ~ 4

Author(s):

L. YANG ◽

Y. C. ZHOU ◽

W. G. MAO ◽

Q. X. LIU

Keyword(s):

Impedance Spectroscopy ◽

Thermal Barrier Coatings ◽

Bond Coat ◽

Equivalent Circuit Model ◽

Isothermal Oxidation ◽

Thermally Grown Oxide ◽

Thermal Barrier ◽

Air Plasma ◽

Barrier Coatings ◽

Plasma Sprayed

In this paper, the impedance spectroscopy technique was employed to examine nondestructively the isothermal oxidation of air plasma sprayed (APS) thermal barrier coatings (TBCs) in air at 800°C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also used to characterize the microstructure evolution of TBCs. After oxidation, the thermally grown oxide (TGO), which was mainly composed of alumina as confirmed by EDX, formed at the upper ceramic coat/bond coat interface, the lower bond coat/substrate interface, and the bond coat. Impedance diagrams obtained from impedance measurements at room temperature were analyzed according to the equivalent circuit model proposed for the TBCs. Various observed electrical responses relating to the growth of oxides and the sintering of YSZ were explained by simulating the impedance spectra of the TBCs.

Download Full-text

Microstructure and Oxidation Resistance of Thermal Barrier Coatings with Different Ceramic Layer

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.320.31 ◽

2021 ◽

Vol 320 ◽

pp. 31-36

Author(s):

Marek Góral ◽

Tadeusz Kubaszek ◽

Barbara Kościelniak ◽

Marcin Drajewicz ◽

Mateusz Gajewski

Keyword(s):

Thermal Barrier Coatings ◽

Bond Coat ◽

Ceramic Layer ◽

Thermal Barrier ◽

Elemental Mapping ◽

Stabilized Zirconia ◽

Barrier Coatings ◽

Bond Coats ◽

All Ceramic ◽

Zirconia Oxide

Thermal barrier coatings are widely used for protection of gas turbine parts against high temperature oxidation and hot corrosion. In present work the microstructural assessment of TBCs produced by atmospheric plasma spray (APS) method was conducted. Three types of ceramic powders were used: magnesia- stabilized zirconia oxide (Metco 210), yttria stabilized zirconia oxide (YSZ -Metco 204) and fine-grained YSZ – Metco 6700. As a base material the Inconel 713 was used as well and CoNiCrAlY was plasma sprayed (APS) as a bond coat. The thickness of all ceramic layers was in range 80 – 110 μm. The elemental mapping of cross-section of magnesia-stabilized zirconia showed the presence of Mg, Zr and O in outer layer. In the YSZ ceramic layer the Y, Zr and O were observed during elemental mapping. The isothermal oxidation test was conducted at 1100 °C for 500 h in static laboratory air. On all samples the delamination and spallation of ceramic layers was observed. Chemical composition analysis of coatings showed the presence of two areas: the first one contained elements from bond coats: Ni, Cr, Al, Co and second area contained O, Cr Co and O that suggest the scale formation. The obtained results showed the total degradation of all ceramic layers as a result of internal stresses in bond-coat. Microscopic analysis showed the areas with complete degradation of bond coats and formation of thick oxides layer.

Download Full-text