Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Song, Dowon; Paik, Ungyu; Guo, Xingye; Woo, Ta-Kwan; Lu, Zhe; Jung, Sung-Hoon; Lee, Je-Hyun; Jung, Yeon‐Gil

doi:10.1016/j.surfcoat.2016.07.112

Cited by 27 publications

(15 citation statements)

References 25 publications

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“…The most severe microstructural degradation was observed in sample A, which showed large crack formations because of the repeated thermal shocks. Vertical cracks initiated from the surface because of rapid volume shrinkage during N 2 quenching, and they grew into large cracks through preexisting splats or pores under repeat of thermal shock, which was observed similarly in previous work [44]. Large horizontal cracks were generated near the interface because there was thermal stress from CTE mismatch between the top and bond coats, which could result in the failure of TBCs.…”

Section: Thermal Durability Evaluationsupporting

confidence: 67%

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

Song

Paik

et al. 2019

Coatings

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In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents.

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Section: Thermal Durability Evaluationsupporting

confidence: 67%

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

Song

Paik

et al. 2019

Coatings

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“…12 the is the elastic modulus of the ceramic materials. In our previous study [33], The E values which were measured by nano-indentation for YGYZ top coat, and the RP-YSZ and HP-YSZ buffer layers, which were determined to be 113.9 ± 23.8 GPa, 123.0 ± 23.8 GPa and 121.0 ± 21.7 GPa, respectively.…”

Section: Accepted Manuscriptmentioning

confidence: 96%

Effect of thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings

Lyu

Choi

et al. 2019

Surface and Coatings Technology

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2019). Effect of thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings. Surface and Coatings Technology. AbstractThe effects of thermal cycling frequency and buffer layer on the crack generation and thermal fatigue behaviors of Yb-Gd-Y-stabilized zirconia (YGYZ)-based thermal barrier coatings (TBCs) were investigated through thermally graded mechanical fatigue (TGMF) test. TGMF tests with low-(period of 10 min) and high-frequency (period of 2 min) cycling were performed at 1100 o C with a 60 MPa tensile load. Different cycling frequencies in TGMF test generate two kinds of crack propagation modes. The sample with low-frequency cycling condition shows penetration cracks in the YGYZ top coat, and multiple narrow vertical cracks are generated in high-frequency cycling. To enhance the thermomechanical properties, different buffer layers were introduced into the TBC systems, which were deposited with the regular (RP) or high-purity 8 wt% yttria stabilized zirconia (HP-YSZ) feedstock. The purity of the feedstock powder used for preparing the buffer layer affected the fracture behavior, showing a better thermal durability for the TBCs with the HP-YSZ in both frequency test conditions. A finite element model is developed, which takes creep effect into account due to thermal cycling. The model shows the high stresses at the interfaces between different layers due to differential thermal expansion. The failure mechanisms of YGYZ-based TBCs in TGMF test are also proposed. The vertical cracks are preferentially created, and then the vertical and horizontal cracks will be propagated when the vertical cracks are impeded by pores and micro-cracks.

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“…The buffer layer is introduced between the top and bond coats, which can reduce stresses generated at the interface due to the CTE mismatch between the top and bond coats during cyclic thermal exposure. In addition, in a previous study [13], layered LZO-based TBCs were already investigated through furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock tests.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Fracture behavior and thermal durability of lanthanum zirconate-based thermal barrier coatings with buffer layer in thermally graded mechanical fatigue environments

Lyu

Kim

Lee

et al. 2017

Surface and Coatings Technology

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The effects of buffer layer on the fracture behavior and lifetime performance of lanthanum zirconate (La 2 Zr 2 O 7 ; LZO)-based thermal barrier coatings (TBCs) were investigated through thermally graded mechanical fatigue (TGMF) tests, which are designed to simulate the operating conditions of rotating parts in gas turbines. To improve the thermal durability of LZO-based TBCs, composite coats consisting of two feedstock powders of LZO and 8 wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing different volume ratios (50:50 and 25:75, respectively). The composite coat of 50:50 volume ratio was employed as the topcoat, and two types of buffer layers were introduced (25:75 volume ratio in LZO and 8YSZ, and 8YSZ only). These TBC systems were compared with a reference TBC system of 8YSZ. The TGMF tests with a tensile load of 60 MPa were performed for 1000 cycles, at a surface temperature of 1100 C and a dwell time of 10 min, and then the samples were cooled at room temperature for 10 min in each cycle. For the single-layer TBCs, the composite topcoat showed similar results as for the reference TBC system. The triple-layer coating (TLC) showed the best thermal cycle performance among all samples, suggesting that the buffer layer was efficient in improving lifetime performance. Failure modes were different for the TBC systems. Delamination and/or cracks were created at the interface between the bond and topcoats or above the interface in the single-layer TBCs, but the TBCs with the buffer layer were delaminated and/or cracked at the interface between the buffer layer and the topcoat, independent of buffer layer species. This study allows further understanding of the LZO-based TBC failure mechanisms in operating conditions, especially in combined thermal and mechanical environments, in order to design reliable TBC systems.

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Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Cited by 27 publications

References 25 publications

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

Effect of thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings

Fracture behavior and thermal durability of lanthanum zirconate-based thermal barrier coatings with buffer layer in thermally graded mechanical fatigue environments

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