Thermal barrier coatings (TBCs) play a pivotal role in protecting the hot structures of modern turbine engines in aerospace as well as utility applications. To meet the increasing efficiency of gas ...turbine technology, worldwide research is focused on designing new architecture of TBCs. These TBCs are mainly fabricated by atmospheric plasma spraying (APS) as it is more economical over the electron beam physical vapor deposition (EB-PVD) technology. Notably, bi-layered, multi-layered and functionally graded TBC structures are recognized as favorable designs to obtain adequate coating performance and durability. In this regard, an attempt has been made in this article to highlight the structure, characteristics, limitations and future prospects of bi-layered, multi-layered and functionally graded TBC systems fabricated using plasma spraying and its allied techniques like suspension plasma spray (SPS), solution precursor plasma spray (SPPS) and plasma spray –physical vapor deposition (PS-PVD).
As one of the promising methods that can be employed to fabricate high-performance thermal barrier coatings (TBCs), suspension plasma spraying (SPS) or solution precursor plasma spraying (SPPS) has ...received significant attention in academic research. Enhanced performances have been shown in the SPS-/SPPS-coatings due to their special microstructures, such as uniformly distributed micro-pores, vertical cracks or columnar structures. Since there are more complexities than conventional plasma spraying methods, many works have been devoted to study the mechanism and properties of SPS-/SPPS-coatings during the past decades. In this work, the latest development of SPS or SPPS is reviewed in order to discuss some key issues in terms of preparation of suspension or solution precursor, injection mode of liquid phase, interaction between liquid and plasma jet, microstructure of as-sprayed coatings and corresponding deposition mechanism. Meanwhile, the potential application of SPS or SPPS in some new-type TBCs is introduced at the end of this paper.
•HfC coatings modified with different TaC content were prepared by supersonic atmosphere plasma spraying.•Appropriate amount of TaC greatly enhanced the ablation performance of HfC coating.•Finite ...Element Analysis was employed to acquire the temperature distribution on the coating surface.•The scale composed of HfO2, Ta2O5 and Hf6Ta2O17 can effectively impede oxygen diffusion and resist airflow scouring.
HfC coatings modified with different TaC contents were designed and successfully deposited on SiC-coated carbon/carbon (C/C) composites by supersonic atmosphere plasma spraying. The phase composition, morphology, and ablation resistance were surveyed, and the structural evolution of the oxide layer was studied as well. Results indicated that HfC coating with 10 vol.% TaC exhibited superior ablation resistance compared with the other compositions, as proved by the ablation rates and surface morphologies. The optical HfC/TaC volume fraction offers an oxide layer with adequate unmelted particles (HfO2 and Hf6Ta2O17) withstanding airflow scouring and moderate liquid phase (Ta2O5) impeding oxygen infiltration.
A Perspective on Plasma Spray Technology Vardelle, Armelle; Moreau, Christian; Themelis, Nickolas J. ...
Plasma chemistry and plasma processing,
05/2015, Volume:
35, Issue:
3
Journal Article
Peer reviewed
Plasma spraying is often assumed to be a mature technology in which all the important phenomena have been observed and described adequately. However, the intricate interactions between the ...electrically conducting fluid and electromagnetic, thermal and acoustics phenomena that affect the operation of the plasma torch are not fully understood as yet. Also, variants of the plasma spray process are emerging and raise new scientific questions. These technologies include the spraying of liquid feedstock in the form of submicrometric particles or chemical precursors in a solvent and, coatings formed by vapor condensation onto the substrate. These relatively novel techniques make possible the production of thinner coatings than in air plasma spraying with a fine and even nanostructured microstructure. This paper attempts to define some of the current important issues and research priorities in the plasma spray field.
MCrAlY coatings are widely preferred in materials used at high temperature applications exposed to oxidation and hot corrosion. The coating process used in the production of thermal spray coatings ...directly affects the microstructure and lifetime of the coating. In this study, a CoNiCrAlY metallic bond coat was deposited on Inconel 718 superalloy substrate material using APS, SSAPS, D-gun, HVOF and CGDS spraying techniques. The produced coatings were subjected to isothermal oxidation tests at 1000 °C for different exposure times. Porosity, surface roughness, XRD, SEM, EDX-elemental mapping analysis were used to investigate and determine the microstructures and the changes in the dimensions of thermally grown oxide (TGO) layer as a function of time and temperature. The obtained data were compared before and after the oxidation tests, and the findings were evaluated considering other related studies within the literature. The results show that CGDS CoNiCrAlY coatings exhibited better oxidation resistance than the coatings produced by the other techniques.
•CoNiCrAlY coating systems were successfully produced by on Inconel 718 substrate using APS, SSAPS, D-gun, HVOF and CGDS techniques.•Changes in the dimensions of TGO layer, microstructural properties and chemical compatibilities of CoNiCrAlY coatings were comparatively investigated as functions of time and temperature.•It was determined that CoNiCrAlY coatings with produced by CGDS technique exhibit superior properties as compared to other techniques.
Recently, nanostructured thermal barrier coatings have received considerable attention because of some superior properties in comparison with their conventional counterpart. In this study, ...nanostructured 8 wt% yttria‐stabilized zirconia (n‐YSZ) coatings were deposited by atmospheric plasma spraying, and the degradation behavior caused by molten calcium‐magnesium‐aluminon‐silicate (CMAS) attack was investigated. Results showed that the thermo‐chemical reaction product between CMAS and YSZ (both powders and coatings) is different with the change of CMAS content. At low CMAS concentration, a cubic phase is generated by the diffusion of Ca into YSZ grains. As compared to the conventional YSZ, less C‐ZrO2 is detected for n‐YSZ. When CMAS reaches a certain concentration (eg 15 mg/cm2), disruptive phase transformation from tetragonal to monoclinic will occur and the reaction is more readily for n‐YSZ. Two different chemical reaction mechanisms governing the CMAS content effect were proposed. It should be noted that the nanozone in the coatings plays an important role in the CMAS degradation process, which enhances CMAS infiltration rate and accelerates the chemical reaction, leading to a poor CMAS resistance of the nanostructured coating than that of the conventional counterpart.
a) When mCMAS/mYSZ ≤0.2, the melt reacts with YSZ fellow a grain boundary attack mechanism and a c‐ZrO2 phase is generated by the diffusion of Ca into the YSZ grains; b) When CMAS increases to a certain concentration, a dissolution‐precipitation reaction occurs instead, in which the original YSZ grains can reprecipitate as Y‐lean m‐ZrO2 after being dissolved by the molten CMAS.
In the present study, TiN/Fe-based amorphous composite coatings with various proportions were fabricated by reactive plasma spraying successfully. The Fe-based amorphous coated with TiH2 powders were ...prepared as feedstock. TiN as reinforcement phases was formed during reactive plasma spraying. The properties investigation indicate that the introduction of TiN does not affect the amorphous forming ability of Fe-based amorphous. And the corrosion resistance and abrasive property are improved due to the introduction of TiN in the composite coatings. The results show that the 15% TiN/Fe-based amorphous composite coating has the most stable performance and is also superior wear-resistant and corrosion resistant.
•TiN/Fe-based amorphous coatings were gained by reactive plasma spraying.•The composite coatings with various proportion component were obtained.•The corrosion resistance of coatings is improved due to the introduction of TiN.•The abrasive property of the composite coating is enhanced.•The 15% TiN/Fe-based amorphous composite coating possesses the best properties.
MCrAlY bond coats with high oxidation resistance are essentially important for improving the life-time of thermal barrier coatings (TBCs). In this study, highly oxidation resistant MCrAlY bond coats ...were prepared by a cost-effective approach involving air plasma spraying (APS) followed by a controlled atmosphere heat treatment (a diffusion treatment performed in a furnace filled with Ar). The results confirmed that a pure α-Al2O3 thermally grown oxide (TGO) was successfully formed on the surface of the heat-treated APS bond coats during isothermal oxidation. The oxidation resistance of the resulting APS bond coats was as high as that of low-pressure plasma sprayed bond coats, which are very expensive. The high oxidation resistance of the APS bond coats fabricated in this study can be attributed to the structural changes of the interface between the splats inside the coating. During the controlled atmosphere heat treatment, the lamellar oxides present between the splats within the as-sprayed APS bond coats converted into isolated oxide particles, and the metal elements could diffuse freely within the coating after the healing of the interface between the lamellar splats. The effect of the changes in the interfacial microstructure of the bond coats on the growth of the TGO was discussed.
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•Controlled atmosphere heat treatment inhibited the formation of mixed-oxide TGO.•TGO growth on heat-treated APS bond coats was as slow as that on LPPS bond coats.•Effect of the changes in the interface microstructure on TGO growth was discussed.
This paper focuses on the oxidation behavior of novel double-ceramic-layer thermal barrier coatings (DCL TBCs) deposited by atmospheric plasma spraying (APS) and suspension plasma spraying (SPS). ...Four kinds of APS-SPS DCL TBCs with dense/porous columnar structured or vertically cracked microstructures were prepared. The oxidation behavior of the APS-SPS DCL TBCs were tested and the underlying mechanisms were further discussed. Results showed that the developed APS-SPS DCL TBCs have a better oxidation resistance than the single layer SPS TBC that was tested for comparison. In the long-term oxidation, the thermally grown oxide (TGO) can be divided into two layers, the outer mixed oxide and inner Al2O3 layer, in which the growth rate of mixed oxide in TGO changed during oxidation. In terms of the oxidation rate and oxidation lifetime, segmented APS-SPS TBCs has a slightly better performance than the columnar APS-SPS TBCs. Among the four different APS-SPS TBCs, the segmented dense APS-SPS TBCs with low vertical crack density appears to have more potential to be used for industrial application.
