Abstract:This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
“…Therefore, vertical crack propagation is promoted by thermal shock. This is consistent with the experimental observation that fast cooling leads to reduced TBC lifetime during thermal cycling in burner rig tests 18 . It is worth noting that the SIF scales with the coating's Young's modulus.…”
Section: Coupled Effect Of Sintering and Thermal Cyclingsupporting
confidence: 89%
“…In the sintering test and real service condition, faster cooling is expected at the coating surface as the engine shuts down (i.e., a thermal shock condition 15, 17, 18 ). The effect of this on the SIF is examined by introducing an intermediate state.…”
Section: Coupled Effect Of Sintering and Thermal Cyclingmentioning
The development of vertical cracks in air plasma sprayed (APS) thermal barrier coatings (TBCs) during thermal cycling and constrained sintering under a temperature gradient is investigated. Microstructural analysis shows that the development of the vertical cracks is associated with multiple processes, including sintering during the hold period and cleavage during cooldown. Inspired by the experimental observations, an image‐based sintering model is used to simulate the development of vertical cracks as the coating sinters while constrained by a substrate. The computational results show that microstructural imperfections can develop into vertical cracks, which then propagate toward the interface. A simple analytical model is presented for the threshold level of in‐plane stress for the onset of propagation of a vertical crack during constrained sintering. By combining the results of these different modeling approaches, the cross‐coupling of the material and geometric parameters, and how this determines the sintering response (microstructure evolution) and vertical crack formation is evaluated. In addition, the growth of vertical cracks by a cleavage mechanism during cooldown is examined and the coupling between sintering, cleavage crack growth, and TBC lifetime is explored.
“…Therefore, vertical crack propagation is promoted by thermal shock. This is consistent with the experimental observation that fast cooling leads to reduced TBC lifetime during thermal cycling in burner rig tests 18 . It is worth noting that the SIF scales with the coating's Young's modulus.…”
Section: Coupled Effect Of Sintering and Thermal Cyclingsupporting
confidence: 89%
“…In the sintering test and real service condition, faster cooling is expected at the coating surface as the engine shuts down (i.e., a thermal shock condition 15, 17, 18 ). The effect of this on the SIF is examined by introducing an intermediate state.…”
Section: Coupled Effect Of Sintering and Thermal Cyclingmentioning
The development of vertical cracks in air plasma sprayed (APS) thermal barrier coatings (TBCs) during thermal cycling and constrained sintering under a temperature gradient is investigated. Microstructural analysis shows that the development of the vertical cracks is associated with multiple processes, including sintering during the hold period and cleavage during cooldown. Inspired by the experimental observations, an image‐based sintering model is used to simulate the development of vertical cracks as the coating sinters while constrained by a substrate. The computational results show that microstructural imperfections can develop into vertical cracks, which then propagate toward the interface. A simple analytical model is presented for the threshold level of in‐plane stress for the onset of propagation of a vertical crack during constrained sintering. By combining the results of these different modeling approaches, the cross‐coupling of the material and geometric parameters, and how this determines the sintering response (microstructure evolution) and vertical crack formation is evaluated. In addition, the growth of vertical cracks by a cleavage mechanism during cooldown is examined and the coupling between sintering, cleavage crack growth, and TBC lifetime is explored.
“…Figure 4 (a) shows photographs of a military helicopter operating in a desert environment, leading to the engine components covered with the re-solidified CMAS sand, and the resulting damage (Fig. 4 b) (Ref 21 , 22 ). Fig.…”
The market needs for increased engine efficiency and environmentally friendly solutions remain the key drivers for the aerospace industry. These efficiency gains will be achieved by meeting the challenges of higher engine operating temperatures, weight reduction, and novel surface solutions for increased component longevity. A critical question to address is if the thermal spray (TS) industry can continue to meet the challenges and demands seen by the airlines and the engine manufacturers. In addition to non-aerospace influences, the COVID-19 pandemic has dramatically affected the landscape of industry growth, not only directly on airlines but also on the associated supply chain. This article reviews this market, its suppliers, and identifies the challenges and opportunities for future growth. Primary focus is on technology and what will be required to bring about reliable, robust, and cost-effective TS solutions into the marketplace. Several issues affecting the global landscape of the aerospace industry are discussed including (1) sustainability, (2) technology, (3) cost of ownership, (4) evolving marketplace, (5) workforce and behavior, and (6) supply chain vitality. An important question to address is if the TS industry can accelerate development with its supply chain and have the ability to commercialize technology more efficiently. Despite the market setbacks from the pandemic and previous issues with the Boeing 737 MAX fleet, the aerospace industry is poised to make significant advancements. These will create new opportunities for thermal spray technology in materials, equipment, and processes. To deliver on them, the implementation of Industry 4.0 along with the investment in human resources is more critical than ever. Based on the findings, the authors project a bright long-term future for both the aerospace and thermal spray industries.
“…Vaben et al used custom-made burner rig to simulate TBC in thermal cyclic condition at 1500 • C, which was equipped with 1050 • C cooling air to determine the effects of transient cooling [58]. Transient cooling during the high temperature exposure of TBC will accelerate the failure.…”
Section: Thermal Cyclic Test Rigmentioning
confidence: 99%
“…TBC was tested under cyclic conditions either by using a custom-made test rig that was equipped with the cooling air system [58][59][60][61]65], that was not equipped with the cooling air system [68], or a commercial test rig that was not equipped with the cooling air system [62,64]. These showed that there are a number of studies have developed test rigs that are capable of simulating TBC-assisted cooling air system.…”
Thermal barrier coating (TBC) and cooling air systems are among the technologies that have been introduced and applied in pursuing the extensive development of advanced gas turbine. TBC is used to protect the gas turbine components from the higher operating temperature of advanced gas turbine, whereas cooling air systems are applied to assist TBC in lowering the temperature exposure of protected surfaces. Generally, a gas turbine operates in three main operational modes, which are base load, peak load, and part peak load. TBC performance under these three operational modes has become essential to be studied, as it will provide the gas turbine owners not only with the behaviors and damage mechanism of TBC but also a TBC life prediction in a particular operating condition. For TBC under base load or so called steady-state condition, a number of studies have been reviewed and discussed. However, it has been found that most of the studies have been conducted without the assistance of a cooling air system, which does not simulate the TBC in advanced gas turbine completely. From this review, the studies on TBC-assisted cooling air system to simulate the advanced gas turbine operating conditions have also been summarized, which are limited to test rig simulations under thermal cyclic mode where thermal cyclic represents peak and part peak load conditions. The equipment used to simulate the gas turbine operating condition, test temperatures, and durations are parameters that have been taken into consideration under this review. Finally, a test rig that is capable of simulating both TBC and cooling air effects at a high operating temperature of advanced gas turbines for prolonged exposure under steady-state condition has been proposed to be developed.
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