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Microstructure, mechanical and thermal properties of YSZ thermal barrier coatings deposited by axial suspension plasma spraying

Poliarus Olena, Morgiel Jerzy, Żórawski Wojciech, Góral Anna, Pomorska Małgorzata, Wojciechowski Krzysztof T., Cherniushok Oleksandr

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no., e89, 2023

EN

Yttrium-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are indispensable elements of present-day turbine propulsion systems. The ones deposited with atmospheric plasma spraying (APS) are characterized by required low thermal conductivity, but they are unable to survive frequent thermomechanical loading and therefore their application is limited to parts remaining stationary. Expanding capability of TBCs is sought in various areas, but the one realized through modification of most proliferated apparatus used for plasma spraying (PS) (from radial to axial injection) and substituting micrometric powders with the nano-structured suspension needs least changes in the industry established procedures and offers the highest property improvement. The present experiment covered the deposition of ZrO2-8Y2O3 YSZ TBC using both atmospheric and suspension PS processes. They were performed with commercial micrometric and nano-structured YSZ (8% Y2O3) powders. The coatings morphology and microstructure were characterized with 3D profilometry, scanning and transmission electron microscopy (SEM/TEM) methods. Finally, the coating’s hardness and heat conductivity were measured. This complex approach allowed to state that PS of micrometric t’-ZrO2 powder having an admixture of m-ZrO2 phase is capable of only partial improvement in its homogenization. However, the suspension PS process of nano-structured powder eliminated any traces of the monoclinic phase from the coating. The TEM microstructure observations indicated that the suspension PS coating is built by in-flight solidified droplets as well as by the melted ones flattened on arrival. A surface layer of liquefied material on solid droplets increases their adhesion to surface asperities promoting pseudo-columnar growth of the coating. The preservation of monotonic slow increase of thermal conductivity during heating of the suspension PS coating means, that its pseudo-columnar microstructure is better suited to withstand high strains during such treatment.

2

Al2O3-TiO2 coatings deposition by intermixed and double injection SPS concepts

Nowakowska Monika, Sokołowski Paweł, Tesař Tomáš, Mušálek Radek, Kiełczawa Tomasz

Materials Science Poland

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2021

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Vol. 39, No. 4

599--614

EN

This work focuses on the study on the novel hybrid method of simultaneous spraying from two different materials (Al2O3 and TiO2) by means of suspension plasma spraying (SPS) using submicron powder and water suspension. The goal was to attempt the deposition of intermixed alumina-titania coatings, namely: Al2O3 + 3 wt.% TiO2, Al2O3 + 13 wt.% TiO2, and Al2O3 + 40 wt.% TiO2. Such compositions are already used but in the form of conventionally plasma sprayed coatings, with micrometer-sized powder. Meanwhile, the injection of feedstocks with submicron-sized particles has not been established yet. In particular, this paper uses two routes of feedstock injection, (i) with the use of an intermixed suspension and (ii) a double injection of separate suspensions. The attention was paid to the characterization of the feedstock materials, description of deposition parameters as well as the morphology, microstructure, and phase composition of the obtained coatings. Among all coatings, Al2O3 + 40 wt.% TiO2 sprayed with double injection contained the most homogeneously distributed and melted splats. The results from this work demonstrate the possibility of coating deposition both by intermixed and double injection concepts but also the need for the further application-relevant optimization, related to the presence of intercolumnar gaps in the microstructure of the coatings.

3

Mechanical Properties and Sliding Wear Resistance of Suspension Plasma Sprayed YSZ Coatings

Łatka Leszek, Szala Mirosław, Macek Wojciech, Branco Ricardo

Advances in Science and Technology. Research Journal

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2020

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Vol. 14, no 4

307--314

EN

In this work, the yttria stabilised zirconia ZrO2 + 8 wt% Y2 O3 (YSZ) coatings were studied. The coatings were manufactured by using a relatively new method based on liquid feedstock, called suspension plasma spraying (SPS). The main aim of the study was to investigate the influence of one of the fundamental process parameters, stand-off distance, on the YSZ coating mechanical properties, namely adhesion, cohesion, hardness, and dry sliding wear resistance. Moreover, the coating surface morphology and microstructure were investigated. Despite the fact that in the SPS method, the heat flux into the substrate is much higher than in conventional atmospheric plasma spraying (APS), for the stand-off distances as short as 40 mm, the structure has not been damaged by thermal stresses. The results revealed that shorter spray distance leads to obtaining the coatings characterised by higher cohesion and adhesion to the substrate as well as higher hardness and resistance to sliding wear. The wear mechanism of both YSZ coatings relies on the adhesive mode, which is intensified by severe coating material delamination.

4

Thermal barrier coatings manufactured by suspension plasma spraying - a review

Łatka L.

Advances in Materials Science

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2018

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Vol. 18, nr 3(57)

95--117

EN

Thermal barrier coatings (TBC) is one of the most intensively studied of coatings’ applications area. From 1970’s TBC are developed in two independent ways: (i) development in new materials, with lower thermal conductivity, better erosion resistance and better thermal shock resistance or (ii) development in new deposition techniques. On this field besides conventional atmospheric plasma spraying (APS) and almost conventional (because of very common use) EB-PVD method, in the past 20 years two new techniques have been developed, namely suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS). In this paper only SPS method was described, as well as, new materials, which could be used in industrial applications of TBC. Moreover, the key issues, like suspension preparation, type of suspension injection, interaction between liquid droplets and plasma jet and deposition mechanism were described.

5

Mikrostruktura powłok Al2O3 natryskanych plazmowo z zawiesin

Żórawski W.

Inżynieria Powierzchni

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2014

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nr 4

19--22

PL

W pracy przedstawiono wyniki badań mikrostruktury powłoki natryskanej plazmowo z zawiesin zawierającej nanometryczne i submikronowe ziarna Al2O3. Natryskana powłoka charakteryzowała się mikrostrukturą bi-modalną, składającą się z obszarów całkowicie przetopionych oraz z obszarów częściowo przetopionych zawierających połączone ze sobą nanoziarna proszku Al2O3.

EN

This paper presented results of microstructure researches of the plasma sprayed coating with application of Al 2O3 powder suspension containing nanometric i submikron grains. The sprayed coating showed a bi-modal structure composed of both fully melted region and partially melted regions included connected nanograins of Al2O3 powder.

6

Warstwy drobnoziarniste otrzymywane metodą natryskiwania plazmowego zawiesin

Tomaszek R., Pawłowski L., Znamirowski Z., Zdanowski J.

Elektronika : konstrukcje, technologie, zastosowania

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2005

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Vol. 46, nr 6

26-27

PL

Przedstawiono wyniki badań mikrostruktury warstw otrzymanych metodą natryskiwania plazmowego zawiesin. Powierzchnię i przekroje warstw analizowano za pomocą skaningowego mikroskopu elektronowego (SEM). Struktura krystaliczna proszku tworzącego zawiesinę oraz produkty transformacji fazowych w warstwie zostały przebadane dyfraktometrem rentgenowskim (XRD).

EN

The paper deals with microstructural characterization of suspension plasma sprayed coatings. Surface and sections of the coatings were investigated using scanning electron microscope (SEM). Crystal structure of initial powder/suspension and resulted phase transformations in coatings were analyzed using X-Ray diffraction.