Wyniki 1-8 spośród 8 dla zapytania: authorDesc:"Anna JASIK"


  W artykule przedstawiono przykład zastosowania obliczeń numerycznych metodą elementów skończonych, jako narzędzia charakteryzującego rozkład temperatury w powłokowych barierach cieplnych o różnego rodzaju ceramicznych warstwach izolacyjnych. Dokonano analizy rozkładu temperatury w powłokach o różnej grubości. Założono zastosowanie konwencjonalnego tlenku cyrkony modyfikowanego tlenkiem itru (8YSZ) oraz nowego typu materiału ceramicznego z grupy tzw. pirochlorów o wzorze La2Zr2O7. Słowa kluczowe: rozkład temperatury, powłokowa bariera cieplna, MES MODELLING OF TEMPERATURE DISTRIBUTION IN THE THERMAL BARRIER COATINGS The paper presents an example of application of numerical calculations using finite element method as a tool of temperature distribution characterization in thermal barrier coatings based on different type pf outer ceramic insulation layers. The paper shows the results of the temperature distribution in ceramic layers with different thickness. As an outer layer the conventional yttria stabilized zirconia (8YSZ) and pyrochlore type material with formula La2Zr2O7 were used. Keywords: temperature distribution, TBC, FEM Wprowadzenie Konieczność zwiększenia sprawności turbin silników lotniczych, a także turbin gazowych stacjonarnych, wymaga poszukiwania rozwiązań, które umożliwiłyby podniesienie temperatury pracy krytycznych części silników wykonanych z nadstopów niklu podczas eksploatacji [5]. Zwiększenie sprawności osiąga się głównie poprzez wzrost temperatury gazów na wylocie z turbiny. W silnikach lotniczych temperatura gazów w komorze spalania osiąga wartość 1500°C [7], podczas gdy temperatura topnienia stopów niklu wynosi ok. 1450°C. Jednym z rozwiązań przyjętych dla zwiększenia sprawności turbin mogłoby być wykorzystanie wysokotopliwych stopów metali: niobu lub molibdenu, jednakże ich wadą jest duża skłonność do korozji. Wobec tego opracowano inny skuteczny sposób, jakim są powłokowe bariery cieplne (TBC — the[...]

The numerical analysis of stress and temperature distribution in a double-ceramic-layer (DCL) type of La2Zr2O7/8YSZ thermal barrier coatings (TBC) in as-sprayed state DOI:10.15199/40.2018.12.3

  1. Introduction When designing multiple devices and machines, designers seek to find a number of solutions to improve the quality, durability and efficiency of both the existing and new designs. The problem of degradation of the working surface of parts of machines and devices, which is connected with the deterioration of their usefulness, may be an example. The wear can be caused by a number of different physical and chemical processes occurring during operation [1-3]. One of the most common cases of wear or damaged to working surface is their degradation under high temperatures. In order to protect the surfaces of components against high temperatures, insulating ceramic coatings are applied to the working surfaces of machine parts and devices. In the case of fixed and variable temperature fields, thermal barrier coatings (TBC) can perform the role of protective coatings. One of the most important stages in the design of ceramic coatings on the surface of machines and devices is the assessment of their effort during operation. TBC can cause a remarkable decrease in the substrate temperature. Therefore, due to the lowered thermal gradient in the substrate, a considerable increase in the fatigue life is anticipated [4]. The action of fixed and variable temperature fields results in deformation and strain known in the literature as thermal stress [5]. Thermal stresses induced in ceramic coatings may affect their durability, as well as have a decisive importance in the quality of work of these coatings. Hence, it is very important to correctly determine the states of their effort at the heat load [5-7]. Due to the complex structure of the coating in the micro scale and the lack of accurate experimental determination of temperatures in the ceramic layer itself, the process is more complicated. Thermal barrier coatings play an important role in reducing temperature of high temperature components and protecting them (e.g. superalloy[...]

The influence of bond-coat thickness on the temperature distribution and stress level in thermal barrier coatings system DOI:10.15199/40.2019.2.2

  1. Introduction One of the solutions used to protect the surface of elements against high temperatures is the use of ceramic coatings obtained by applying them by thermal spraying processes on the working surfaces of elements of machines and equipment. Thermal Barrier Coatings (TBC) can be used as protective coatings in the case of constant and variable temperature fields. The following issues are closely related to the problems of evaluation of the critical stress-strain state of elements with applied ceramic coatings subjected to thermal loads: - heat exchange, - presentation of temperature field distribution of the tested ceramic coatings through the use of numerical calculation methods, - strength of materials, taking into account loads originating from the temperature field. Strength analysis of the tested objects with ceramic coatings subjected to thermal loads requires knowledge of the properties of the analysed object, including knowledge of the properties of the materials of both the object and the coating. For this reason the presence of this issue in the literature is also extensively examined. Starting from the basics of ceramic materials science in papers [1-8] to the evaluation of mechanical properties in [1,4,9]. Depending on the material used, ceramic coatings are characterised by different parameters that determine their application. These papers primarily focused on ceramic coatings constituting thermal barriers used mainly in combustion engines and jet engines. Thermal Barrier Coatings are the basic method of surface protection, which, together with internal air cooling, makes it possible to increase the durability of components in the hot section of gas turbines of aircraft engines [10]. The use of this type of coatings also makes it possible to increase the temperature of exhaust gases, and thus to improve the efficiency of gas turbines, both stationary and aircraft types [11]. PhD Anna Jasik - is an ass[...]

Degradation of La2Zr2O7thermal barrier coatings DOI:10.15199/40.2018.6.3

  1. Introduction TBC coatings found wide application as protective coatings for elements of a hot section of gas turbines such as combustion chambers, which, on the one hand, enables an increase in durability of such elements in conditions of complex stresses and high temperature [4,11]. On a standard basis, commercially used layers are deposited on a monolayer system based on the ZrO2 phase, which was modified with yttrium oxide, Y2O3, which ensures high strength properties for the whole TBC system. However, these layers have limited durability, as a result of sintering, and exhibit phase changes in the ceramic layers, due to the long- -lasting impact of a high temperature [2,8]. The newest solutions in this area are related to deposition of new ceramic materials, such as zirconates of rare earth elements as insulating materials in TBC systems. Those ceramic materials are characterized by e.g. better thermal properties (i.e. mainly lower thermal conductivity coefficient), higher resistance against outer corrosion or erosion environments, with simultaneously worse e.g. thermal-chemical compatibility with oxides that comprise the TGO zone or a value of linear extension so low, that direct application of a homogeneous layer would make it fall offof the surface of an interlayer [1,6- 7,9-10,13]. In order to meet the demand of highly stringent operating environments, it is essential to develop new materials for TBC. Recently, the compound with pyrochlore phase, i.e. lanthanum zirconate, exhibited some very interesting properties, making it a promising candidate for TBC materials. The earlier works indicated that this material has excellent thermal stability (up to its melting point 2573 K), low thermal conductivi- Artykuł naukowy DOI: 10.1[...]

Degradation of La2Zr2O7+8YSZ composite TBC systems during oxidation at temperature of 1100°C DOI:10.15199/40.2019.4.1

  1. Introduction Thermal barrier coating (TBC) systems are one the most modern materials and technological solutions in area of materials and surface engineering. They are usually used to protection of hot-section components of stationary and aircrafts gas turbine engines such as combustion chamber and vanes. This system typically consists the Ni-based superalloy substrate, a bond coat based also on the superalloys with high oxidation/corrosion resistance and an insulating ceramic topcoat built usually from zirconia - based ceramic. A thin thermally grown oxide (TGO) layer is formed also between bond coat and ceramic layer, and this area is the most important from destruction processes point of view [3,7,4]. The mostly used ceramic materials dedicated to insulation layer is yttria-stabilized zirconia with addition of 6-8% wt. of yttria (8YSZ) with metastable tetragonal type of lattice. The thermal conductivity of 8YSZ ceramic( 2.2 W/mK) is a referential values for other new ceramic dedicated for low-k TBC systems [4]. The widely investigated materials for replacement of the 8YSZ are the rare-earth pyrochlore zirconates with overall formula RE2Zr2O7 (where RE is a rare-earth lanthanide) and pyrochlore type of lattice. Generally the thermal conductivity of these materials is as low as 1.5 W/mK, and can be still reduced. Undesirable features of those materials is a very low fracture toughness which strongly limited durability of whole system especially in the terms of thermal cyclic life [1,2,6,8,9,12,16,17]. The most important parameters related with development of TBC systems are related with decreasing of thermal conductivity and increasing of fracture thoroughness. The fracture toughness can be improved by modifying the chemistry of materials and modifying the morphology and microstructure or ‘design architecture’ (e.g., composite or multilayer). Previous research on composites and multilayers thermal barrier syst[...]

Modelowanie fizyczne szkliwienia powierzchni powłokowych barier cieplnych typu Gd2Zr2O7 podczas obróbki laserowej

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Powłokowe bariery cieplne (TBC - thermal barier coatings) są stosowane w celu ochrony powierzchni metalicznych w gorącej sekcji turbin gazowych. Ma to zapewnić zwiększenie trwałości i bezpieczną eksploatację w warunkach długotrwałej pracy silnika w wysokiej temperaturze. Zazwyczaj powłoki tego typu stanowi system dwóch warstw. Zewnętrznej, natryskiwanej plazmowo w powietrzu, ceramicznej warstwy izolującej na bazie częściowo stabilizowanego tlenkiem itru tlenku cyrkonu oraz warstwy wewnętrznej, podkładowej natryskiwanej plazmowo w próżni z proszków typu Ni(Co)CrAlY. Zewnętrzna, porowata warstwa ceramiczna spełnia rolę izolacji cieplnej, natomiast wewnętrzna warstwa podkładowa zapewnia z jednej strony odporność na utlenianie i korozję wysokotemperaturową, z drugiej kompensuje różnice w wartościach współczynnika liniowej rozszerzalności cieplnej warstwy ceramicznej i stopu podłoża [1, 2]. Podstawową cechą morfologiczną warstwy ceramicznej jest obecność porów i pęknięć wertykalnych oraz horyzontalnych. Rolą celowo kreowanej siatki pęknięć i porów jest zwiększenie zdolności izolacyjnych warstwy ceramicznej, ale także zmniejszenie naprężeń wewnętrznych. Z drugiej strony obecność pęknięć i porów obniża podstawowe właściwości mechaniczne, a także negatywnie wpływa na odporność na utlenianie i korozję wysokotemperaturową całego systemu TBC [1÷4]. Obecność pęknięć i porów ułatwia penetrację warstwy ceramicznej przez powietrze i agresywne gazy robocze oraz ciekłe osady solne, co ułatwia proces degradacji warstw TBC. Infiltracja powietrza wewnątrz powłoki powoduje przyspieszoną degradację warstwy podkładowej i przyrost grubości tlenków TGO (thermally grown oxides). W konsekwencji następuje przyspieszone pękanie i odpadanie warstwy ceramicznej [5]. Proces infiltracji może zostać spowolniony przez przetopienie powierzchni warstwy ceramicznej za pomocą wiązki laserowej. Operacja ta pozwala na zmniejszenie chropowatości warstwy wierzchniej,[...]

Surface condition of La2Zr2O7 based TBC system after hot corrosion in molten sulfate Na2SO4 salts DOI:10.15199/40.2019.3.4

  1. Introducion Resistance against degradation under aggressive liquid deposit conditions is one of the most important aspects in determining the overall durability of thermal barrier coatings systems. This problem is also an area of intensive investigations related to designing new ceramic materials that demonstrate resistance against liquid deposits. The presence of these sediments is the result of impurities located in the fuel, such as sulfur, phosphorus, calcium, potassium, sodium and vanadium among others [3]. At high operating temperatures, the liquid deposits “stick" to the working surface of high-temperature elements in a turbine. Then, they melt and react with the surface material (metallic substrate or coatings, as well as PhD Anna Jasik - is an assistant professor in the Faculty of Materials Engineering and Metallurgy of the Silesian University of Technology. In 1999 she graduated from the Faculty of Metallurgy at the Silesian University of Technology, then in the years 1999-2005 she was a PhD student in the field of Materials Science and Metallurgy. The scope of her scientific interests includes new ceramic materials with very good insulating properties, especially on the basis of zirconium oxide modified with oxides of rare earth elements. She does research in the field of numerical simulations using the finite element method (FEM) of state of stress and temperature distribution in multilayer thermal sprayed coatings, primarily in coating thermal barriers (TBC). She is the author and co-author of many scientific publications in this area published in recognized journals of national and international range. E-mail: anna.jasik@polsl.pl Grzegorz Moskal, DSc, PhD, Eng. Associated Prof. - born in 1975 y. in Chorzow. An employee of the Faculty of Materials Science and Metallurgy of the Silesian University of Technology. In 1999 he was graduated in Faculty of Materials Engineering and Metallurgy and in the years 1999-2004 he[...]

The influence of yttrium addition on thermogravimetric behaviour of new Co-10Al-5Mo-2Nb Co-based superalloy DOI:10.15199/40.2018.11.1

  1. Introduction Creep resistant alloys were the most important group of materials and they decide about development direction of materials science in area of chemical and phase constituent designing, modelling and casting technology. Last decades showed that there are impassable limit such as melting temperature and in consequence the further development of those alloys seemed impossible. However, if it is not possible to exceed the melting temperature barrier, it is possible to increase the temperature range of the exploitation of alloys by modifying the alloys microstructure and introducing phases with more stability. The best cachet of such actions is development of new type of Co-based superalloys strengthened by L12 phase, the same like in γ/γ` Ni-based superalloys. This new group of alloys based not on the solid solution and carbide hardening effect such as Haynes 188 and Alloy 255, but is hardened by cubical precipitation of γ`- Co(Al,X)3 phase with L12 type of lattice (where X=W, Mo, Nb, Ta) [1-4]. This group of alloys is basing on Co-Al-W or Co-Al-(Mo,Nb,Ta) systems and the most intensively investigated are alloys such as Co-9Al-9W and Co-7Al-5Mo-2Nb (at. %), as an tungsten-fee alloys [1,4]. This structure is very similar to γ/γ` that is obtained for Ni-based superalloys. The consequences of this differences are related with mainly better creep properties of new L12 strengthened superalloys, but with lower oxidation resistance than conventional Co-based superalloys [5,6]. The oxidation properties of new Co-based superalloys at temperature above 800°C is steel relatively poor what is related with formation of complex multilayered oxide scale based on CoO, CoAl2O4 and CoWO4 oxides [7-16]. The oxidation resistance of Co- Al-W alloys improved by different alloying elements in many publications and revealed beneficial effect of Cr, Si, Ta, B etc. [8-11,13,16]. But in the case of tungsten free alloys [...]

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