Research

12 pages, 4185 KiB

Open AccessArticle

Room- and high temperature Wear Resistance of MCrAlY Coatings Deposited by Detonation Gun (D-gun) and Supersonic Plasma Spraying (SSPS) Techniques

by Mehmet Kilic, Dervis Ozkan, Mustafa Sabri Gok and Abdullah Cahit Karaoglanli

Coatings 2020, 10(11), 1107; https://doi.org/10.3390/coatings10111107 - 19 Nov 2020

Cited by 17 | Viewed by 2470

Abstract

In this study, CoNiCrAlY metallic coatings were deposited on an Inconel 718 nickel-based superalloy substrate material using the detonation gun (D-gun) and supersonic plasma spraying (SSPS) techniques. The microstructural and mechanical properties in addition to their room and high temperature wear behavior of [...] Read more.

In this study, CoNiCrAlY metallic coatings were deposited on an Inconel 718 nickel-based superalloy substrate material using the detonation gun (D-gun) and supersonic plasma spraying (SSPS) techniques. The microstructural and mechanical properties in addition to their room and high temperature wear behavior of the produced coatings were evaluated. The wear tests were performed at room temperature (rt), 250 and 500 °C using 2N and X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses of the worn coatings were performed to assess their wear performance. The coatings produced with D-gun process exhibited higher hardness and lower porosity (550 ± 50 HV_0.25 hardness and 1.2 ± 1.0% porosity) than SSPS coatings (with 380 ± 30 HV_0.25 hardness and 1.5 ± 1.0% porosity) which resulted in better room- and high temperature wear performance for D-gun coatings. The worn surfaces of both coatings exhibited formation of tribological layers and superficial microstructural changes by varying temperature and load conditions. Increasing load and temperature resulted in increased wear loss whereas increasing temperature resulted in reduced COF values for both coatings. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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15 pages, 32859 KiB

Open AccessArticle

Interaction of Strontium Zirconate Plasma Sprayed Coating with Natural Silicate (CMAS) Dust—Origin of Luminescent Phases

by Pavel Ctibor

Coatings 2020, 10(8), 738; https://doi.org/10.3390/coatings10080738 - 28 Jul 2020

Cited by 3 | Viewed by 2127

Abstract

Strontium zirconate (SrZrO₃) commercial powder was plasma sprayed using a high-feedrate water-stabilized plasma system (WSP) torch. Coatings with a thickness of about 1 mm were produced. Now, we are concentrating on a topic never addressed for pure SrZrO₃ coatings: how [...] Read more.

Strontium zirconate (SrZrO₃) commercial powder was plasma sprayed using a high-feedrate water-stabilized plasma system (WSP) torch. Coatings with a thickness of about 1 mm were produced. Now, we are concentrating on a topic never addressed for pure SrZrO₃ coatings: how the coatings interact with natural dust, known as calcium-magnesium-aluminum-silicate (CMAS). We selected various regimes of thermal treatment where SrZrO₃ coatings were exposed to CMAS, and studied chemical changes, phase changes and the microstructure evolution of the influenced coatings. Microhardness of the exposed coatings was monitored as well. The results would help to understand, how the excellent refractory material SrZrO₃ interacts with natural silicates. We kept in mind that pure SrZrO₃ is not optimal for a thermal barrier application because of high-temperature phase transformations, but to study the CMAS-induced phenomena in more complex compositions, for example La₂Zr₂O₇-SrZrO₃, is difficult and interpretations have not been completed currently. The value of the actual research is in the separation of the phenomena typical just for SrZrO₃. A potential for newly developed phases to serve as a sacrificial components of various barrier-coating systems is discussed. Several physical aspects of the newly developed components are discussed as well, namely the luminescence. Here the dust-based phases shifted down the temperature at which luminescence can occur in pure SrZrO₃ ceramics. The entire thickness of influenced layers was relatively high, around 300 µm. The amorphous component, predominant after short-term CMAS exposure, was subsequently crystallized to various phases, namely SrSiO₃ and monoclinic as well as tetragonal zirconia. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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15 pages, 7985 KiB

Open AccessArticle

Experimental and Modeling Studies of Bond Coat Species Effect on Microstructure Evolution in EB-PVD Thermal Barrier Coatings in Cyclic Thermal Environments

by Zhe Lu, Guanlin Lyu, Abhilash Gulhane, Hyeon-Myeong Park, Jun Seong Kim, Yeon-Gil Jung and Jing Zhang

Coatings 2019, 9(10), 626; https://doi.org/10.3390/coatings9100626 - 28 Sep 2019

Cited by 9 | Viewed by 3586

Abstract

In this work, the effects of bond coat species on the thermal barrier coating (TBC) microstructure are investigated under thermal cyclic conditions. The TBC samples are prepared by electron beam-physical vapor deposition with two species of bond coats prepared by either air-plasma spray [...] Read more.

In this work, the effects of bond coat species on the thermal barrier coating (TBC) microstructure are investigated under thermal cyclic conditions. The TBC samples are prepared by electron beam-physical vapor deposition with two species of bond coats prepared by either air-plasma spray (APS) or high-velocity oxygen fuel (HVOF) methods. The TBC samples are evaluated in a variety of thermal cyclic conditions, including flame thermal fatigue (FTF), cyclic furnace thermal fatigue (CFTF), and thermal shock (TS) tests. In FTF test, the interface microstructures of TBC samples show a sound condition without any delamination or cracking. In CFTF and TS tests, the TBCs with the HVOF bond coat demonstrate better thermal durability than that by APS. In parallel with the experiments, a finite element (FE) model is developed. Using a transient thermal analysis, the high-temperature creep-fatigue behavior of the TBC samples is simulated similar to the conditions used in CFTF test. The FE simulation predicts a lower equivalent stress at the interface between the top coat and bond coat in bond coat prepared using HVOF compared with APS, suggesting a longer cyclic life of the coating with the HVOF bond coat, which is consistent with the experimental observation. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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11 pages, 15119 KiB

Open AccessEditor’s ChoiceArticle

Thermal Stability of YSZ Coatings Deposited by Plasma Spray–Physical Vapor Deposition

by Zefei Cheng, Jiasheng Yang, Fang Shao, Xinghua Zhong, Huayu Zhao, Yin Zhuang, Jinxing Ni and Shunyan Tao

Coatings 2019, 9(8), 464; https://doi.org/10.3390/coatings9080464 - 24 Jul 2019

Cited by 19 | Viewed by 3397

Abstract

The plasma spray–physical vapor deposition (PS–PVD) process has received considerable attention due to its non-line of sight deposition ability, high deposition rates, and cost efficiency. Compared with electron beam–physical vapor deposition (EB–PVD), PS–PVD can also prepare thermal barrier coatings (TBCs) with columnar microstructures. [...] Read more.

The plasma spray–physical vapor deposition (PS–PVD) process has received considerable attention due to its non-line of sight deposition ability, high deposition rates, and cost efficiency. Compared with electron beam–physical vapor deposition (EB–PVD), PS–PVD can also prepare thermal barrier coatings (TBCs) with columnar microstructures. In this paper, yttria-stabilized zirconia (YSZ) coatings were fabricated by PS–PVD. Results showed that the as-deposited coating presented a typical columnar structure and was mainly composed of metastable tetragonal (t′-ZrO₂) phase. With thermal exposure, the initial t′ phase of YSZ evolved gradually into monoclinic (m-ZrO₂) phase. Significant increase in hardness (H) and the Young’s modulus (E) of the coating was attributed to the sintering effect of the coating during the thermal exposure, dependent on exposure temperature and time. However, the values of H and E decreased in the coatings thermally treated at 1300–1500 °C for 24 h, which is mainly affected by the formation of m-ZrO₂ phase. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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10 pages, 9930 KiB

Open AccessEditor’s ChoiceArticle

High Temperature Anti-Friction Behaviors of a-Si:H Films and Counterface Material Selection

by Qunfeng Zeng and Liguo Qin

Coatings 2019, 9(7), 450; https://doi.org/10.3390/coatings9070450 - 18 Jul 2019

Cited by 8 | Viewed by 3427

Abstract

In the present paper, the influence of self-mated friction materials on the tribological properties of hydrogenated amorphous silicon films (a-Si:H films) is studied systemically at high temperature. The results are obtained by comparing the tribological properties of a-Si:H films under different friction pair [...] Read more.

In the present paper, the influence of self-mated friction materials on the tribological properties of hydrogenated amorphous silicon films (a-Si:H films) is studied systemically at high temperature. The results are obtained by comparing the tribological properties of a-Si:H films under different friction pair materials and temperatures. The a-Si:H films exhibit super-low friction of 0.07 at a temperature of 600 °C, and ceramic materials are appropriate for anti-friction behaviors of a-Si:H films at high temperature. The results of tribotests and observations of the fundamental friction mechanism show that super-low friction of a-Si:H films and ceramic materials of the friction system are involved in high temperature oxidation; this also applies to the tribochemical reactions of a-Si:H films, steel and iron silicate in open air at elevated temperature in the friction process. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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12 pages, 5756 KiB

Open AccessArticle

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

by Dowon Song, Taeseup Song, Ungyu Paik, Guanlin Lyu, Yeon-Gil Jung, Baig-Gyu Choi, In-Soo Kim and Jing Zhang

Coatings 2019, 9(6), 365; https://doi.org/10.3390/coatings9060365 - 04 Jun 2019

Cited by 10 | Viewed by 4183

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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15 pages, 5152 KiB

Open AccessArticle

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

by Dowon Song, Taeseup Song, Ungyu Paik, Guanlin Lyu, Yeon-Gil Jung, Baig-Gyu Choi, In-Soo Kim and Jing Zhang

Coatings 2019, 9(6), 358; https://doi.org/10.3390/coatings9060358 - 31 May 2019

Cited by 26 | Viewed by 3369

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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9 pages, 3282 KiB

Open AccessArticle

Hot Corrosion Behavior of BaLa₂Ti₃O₁₀ Thermal Barrier Ceramics in V₂O₅ and Na₂SO₄ + V₂O₅ Molten Salts

by Hui Liu, Jin Cai and Jihong Zhu

Coatings 2019, 9(6), 351; https://doi.org/10.3390/coatings9060351 - 29 May 2019

Cited by 23 | Viewed by 2965

Abstract

BaLa₂Ti₃O₁₀ ceramics for thermal barrier coating (TBC) applications were fabricated, and exposed to V₂O₅ and Na₂SO₄ + V₂O₅ molten salts at 900 °C to investigate the hot corrosion behavior. [...] Read more.

BaLa₂Ti₃O₁₀ ceramics for thermal barrier coating (TBC) applications were fabricated, and exposed to V₂O₅ and Na₂SO₄ + V₂O₅ molten salts at 900 °C to investigate the hot corrosion behavior. After 4 h corrosion tests, the main reaction products resulting from V₂O₅ salt corrosion were LaVO₄, TiO₂, and Ba₃V₄O₁₃, whereas those due to Na₂SO₄ + V₂O₅ corrosion consisted of LaVO₄, TiO₂, BaSO₄ and some Ba₃V₄O₁₃. The structures of reaction layers on the surfaces depended on the corrosion medium. In V₂O₅ salt, the layer was dense and had a thickness of 8–10 μm. While in Na₂SO₄ + V₂O₅ salt, it had a ~15 μm porous structure and a dense, thin band at the bottom. Beneath the dense layer or the band, no obvious molten salt was found. The mechanisms by which the reaction layer forms were discussed. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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13 pages, 3449 KiB

Open AccessArticle

A Novel Method for nZEB Internal Coverings Design Based on Neural Networks

by José A. Orosa, Diego Vergara, Ángel M. Costa and Rebeca Bouzón

Coatings 2019, 9(5), 288; https://doi.org/10.3390/coatings9050288 - 27 Apr 2019

Cited by 3 | Viewed by 2633

Abstract

Research from the International Energy Agency about indoor ambiences and nearly zero energy buildings (nZEB) in the past has been centred on different aspects such as the prediction of indoor conditions as a function of the weather using laboratory material properties for simulations [...] Read more.

Research from the International Energy Agency about indoor ambiences and nearly zero energy buildings (nZEB) in the past has been centred on different aspects such as the prediction of indoor conditions as a function of the weather using laboratory material properties for simulations and real sampled data for validation. Thus, it is possible to use real data for defining behavioural groups of indoor ambiences as a function of real vapour permeability of internal coverings. However, this method is not suitable for modelling it and predicting its behaviour under weather changes, which is of interest to improve the method of selection and use of building construction materials. In this research, artificial intelligence procedures were employed as the first model of permeable coverings material behaviour to provide a newer understanding of building materials and applications for the generation of new control procedures between the mechanical and electronic point of view of building construction materials. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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12 pages, 3625 KiB

Open AccessArticle

Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation

by Sung Yong Chang and Ki-Yong Oh

Coatings 2019, 9(4), 229; https://doi.org/10.3390/coatings9040229 - 31 Mar 2019

Cited by 7 | Viewed by 4317

Abstract

In this study, the contribution of high thermomechanical fatigue to the gas turbine lifetime during a steady-state operation is evaluated for the first time. An evolution of the roughness on the surface between the thermal barrier coating and bond coating is addressed to [...] Read more.

In this study, the contribution of high thermomechanical fatigue to the gas turbine lifetime during a steady-state operation is evaluated for the first time. An evolution of the roughness on the surface between the thermal barrier coating and bond coating is addressed to elucidate the correlation between operating conditions and the degradation of a gas turbine. Specifically, three factors affecting coating failure are characterized, namely isothermal operation, low-cycle fatigue, and high thermomechanical fatigue, using laboratory experiments and actual service-exposed blades in a power plant. The results indicate that, although isothermal heat exposure during a steady-state operation contributes to creep, it does not contribute to failure caused by coating fatigue. Low-cycle fatigue during a transient operation cannot fully describe the evolution of the roughness between the thermal barrier coating and the bond coating of the gas turbine. High thermomechanical fatigue during a steady-state operation plays a critical role in coating failure because the temperature of hot gas pass components fluctuates up to 140 °C at high operating temperatures. Hence, high thermomechanical fatigue must be accounted for to accurately predict the remaining useful lifetime of a gas turbine because the current method of predicting the remaining useful lifetime only accounts for creep during a steady-state operation and for low-cycle fatigue during a transient operation. Full article

(This article belongs to the Special Issue Science and Technology of Thermal Barrier Coatings)

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