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Abstract

Abstract information

English title:	Yttria-stabilized zirconia thermal barrier coatings deposited by atmospheric plasma spraying at CENAPROT: process analysis and infiltration behavior against volcanic ashes
Spanish title:	Recubrimientos barrera t�rmica de zirconia estabilizada con itria depositados por proyecci�n t�rmica en CENAPROT: An�lisis del proceso y comportamiento de infiltraci�n de cenizas volc�nicas
English abstract:	Thermal barrier coatings have enabled the increase of the operational temperature of turbine engines used in air transportation. Increasing the gas turbine temperature critical conditions of safety associated with phase stability for most widely used material 7-8 wt% Yttria stabilized zirconia is reached. In addition to the inherent physicochemical restrictions of Yttria stabilized zirconia at high temperatures, its interaction with siliceous airborne particles at temperatures above 1200 �C has conducted to sediments of calcium-magnesium-aluminum-silicates found in failed engines and represent a major concern since the last decades. The high-temperature isothermal infiltration behavior of volcanic ashes and the corresponding phase stability Yttria stabilized zirconia thermal barrier coatings produced by atmospheric plasma spray are presented here. Three volcanic ashes from the Eyjafjallaj�kull, Colima and Popocatepetl and volcanoes have been used in this work. Also, three sets of /YSZ coatings with low (~ 10%), medium (~ 20%), and high (~ 30%) porosity levels obtained from an optimization process by the design of experiments at CENAPROT are analyzed. Preceding the infiltration experiments, physicochemical characterization of the volcanic ashes were carried out including thermal analyses by differential scanning calorimetry, structural studies by X-ray diffraction, and inductively coupled plasma optical emission spectrometer chemical composition measurements. Thermal barrier coatings infiltration tests were carried out isothermally at 1250 �C for different times. Results showed that for the three thermal barrier coatings porosity levels infiltration depth follows a behavior that can be explained with a parabolic function. Also, higher infiltration kinetics was detected for volcanic ashes with lower SiO2 content. Following these observations, an empirical mathematical model describing isothermal volcanic ashes infiltration on APS-thermal barrier coatings is proposed. For such a model, further asymptotic and linear fittings were performed in order to determine the correlation of infiltration with the chemical composition of the volcanic ashes (expressed in terms of basicity index) and with the microstructure of the coating (expressed in terms of the porosity). The extent of chemical degradation inflicted by volcanic ashes on the Yttria stabilized zirconia coatings is directly related to their silica content. In general, for greater SiO2 values, a higher content of monoclinic ZrO2 was observed. For all volcanic ashes, maximum m-ZrO2 values are seen at intermediate annealing times (2 h - 5 h). This behavior can be correlated with the t-YSZ  m-ZrO2 transformation which occurs with more intensity below 5 h of heat treatment. m-ZrO2 formation takes place at high rates until a maximum content is reached limited by local chemistry conditions of the melt. After that, the formation of ZrSiO4 follows at expense of the m-ZrO2. At such point, there is a competing m-ZrO2 and ZrSiO4 formation which includes local chemistry changes in the melt affecting the viscosity. Such local chemistry becomes more similar for all VAs as time increases, therefore exhibiting higher infiltration similitude as time increases.
Spanish abstract:	Los recubrimientos de barrera t�rmica han permitido aumentar la temperatura de funcionamiento de los turbomotores utilizados en el transporte a�reo. Al aumentar la temperatura de la turbina de gas, se alcanzan las condiciones cr�ticas de seguridad asociadas a la estabilidad de fase del material m�s utilizado, la circonia estabilizada con itria. Adem�s de las restricciones fisicoqu�micas inherentes a la circonia estabilizada con itria a altas temperaturas, su interacci�n con las part�culas sil�ceas del aire a temperaturas superiores a 1200 �C ha conducido a sedimentos de silicatos de calcio-magnesio-aluminio que se encuentran en los motores averiados y representan una gran preocupaci�n desde las �ltimas d�cadas. En este trabajo se estudia la infiltraci�n de cenizas volc�nicas en recubrimientos de barreras t�rmicas a base de zirconia estabilizada con itria, as� como la correspondiente estabilidad de fases a alta temperatura. Para ello se utilizaron muestras de cenizas de los volcanes Eyjafjallaj�kull, Colima y Popocat�petl. As� mismo se realiza el an�lisis del efecto de la microestructura de los recubrimientos de barreras t�rmicas estudiando recubrimientos con baja (~10%), media (~ 20%) y alta (~ 30%) porosidad obtenidos a partir de un proceso de optimizaci�n del proceso por dise�o de experimentos en CENAPROT. Previo a los experimentos de infiltraci�n se estudi� el comportamiento t�rmico, estructural y qu�mico de las cenizas mediante calorimetr�a de barrido diferencial, difracci�n de rayos-X, y espectrometr�a de emisi�n �ptica por plasma acoplado inductivamentente, respectivamente. Los experimentos de infiltraci�n se llevaron a cabo isot�rmicamente a 1250 �C a diferentes tiempos. Los resultados muestran que para todas las microestructuras, la infiltraci�n de las tres cenizas volc�nicas sigue un comportamiento parab�lico. As� mismo, se observ� mayor efecto de infiltraci�n de las cenizas volc�nicas con menor contenido de SiO2. Siguiendo dichas observaciones se plantea un modelo matem�tico que describe el fen�meno de infiltraci�n en funci�n del tiempo. Adicionalmente se realizan an�lisis lineales y asint�ticos para correlacionar la infiltraci�n con la composici�n qu�mica de las cenizas volc�nicas y con la microestructura de los recubrimientos de barreras t�rmicas. Se observa que el grado de degradaci�n qu�mica causada, observada mediante la formaci�n de m-ZrO2, est� relacionada con el contenido de SiO2 en las cenizas volc�nicas. Para mayores contenidos de SiO2 se observa una mayor degradaci�n del recubrimiento. Con las tres cenizas analizadas se observa un contenido m�ximo de m-ZrO2 en tiempos entre 2 h y 5 h. Este comportamiento puede relacionarse con la transformaci�n t-YSZ  m-ZrO2 en los recubrimientos de barreras t�rmicas, que ocurre con mayor intensidad a tiempos menores a 5 h. A tiempos cercanos a 5 h se alcanza un contenido m�ximo de m-ZrO2. Despu�s dicho tiempo se inicia la formaci�n de ZrSiO4 a costa de m-ZrO2. En ese punto se da la competencia en la formaci�n de ambas fases para mantener el equilibrio qu�mico local. Este equilibrio incluye variaciones en la composici�n qu�mica de las cenizas volc�nicas fundidas que afectan su viscosidad. Debido a ello a partir de ese punto la viscosidad de las cenizas volc�nicas es similar y por lo tanto el comportamiento de infiltraci�n muestra mayor similitud a medida que incrementa el tiempo.
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Authors

Name	Institution	Email
Juan Munoz Saldana	Cinvestav-Queretaro	jmunoz@cinvestav.mx
Marco Antonio Rivera Gil	Cinvestav	marivera@cinvestav.mx
Uwe Schulz	Deutsches Zentrum f�r Luft und Raumfahrt	uwe.schulz@dlr.de
David Lozano Mandujano	Cinvestav	davidlozano@cinvestav.mx
Ravisankar Naraparaju	Deutsches Zentrum f�r Luft und Ramufahrt	ravisankar.naraparaju@dlr.de
Gerardo Tr�paga Martinez	Cinvestav	trapaga@cinvestav.mx

Presentation

Room:	Earth
Date:	2 June 2021
Hour:	14:30 - 15:00

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5+1 IMRMPT
5+1 International Meeting for Researchers in Materials and Plasma Technology

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