Study of the structure and mechanical properties in 8 mol% yttria-stabilized zirconia coating manufactured by suspension plasma spraying

RESUMEN: El estudio de recubrimientos nanoestructurados fabricados mediante proyección térmica ha generado un gran interés en las últimas dos décadas debido a su considerable mejora en sus propiedades sobre todo en las propiedades físicas y mecánicas. Esta mejora resulta de reducir los tamaños de grano de su materia prima a escalas de 100 a 1000 veces más bajas comparadas con los recubrimientos convencionales microestructurados. Así, estos recubrimientos con estructuras a nivel nano y/o submicrométrica están empezando a ser usados en la industria gracias a sus sobresalientes propiedades y es fundamental el estudio de sus propiedades mecánicas para determinadas aplicaciones. En la actualidad, la indentación es la principal técnica de caracterización de recubrimientos y películas delgadas, a pesar de estar altamente influenciada por los defectos propios del recubrimiento en la vecindad de la indentación. La nanoindentación y la microindentación se presentan como la mejor opción para evaluar el comportamiento mecánico de estos recubrimientos nanoestructurados. Por esta razón, en este trabajo se analizó el efecto de la estructura de un recubrimiento de circona estabilizada con 8% en mol de itria (8YSZ) elaborado por proyección térmica por plasma a partir de suspensiones nanométricas (SPS) y su relación con sus propiedades mecánicas (dureza y módulo de elasticidad) medidas por las técnicas de nanoindentación y microindentación. El análisis de la estructura de la sección transversal mostró que el recubrimiento exhibe una estructura bimodal, la cual está compuesta por una zona con partículas nanométricas semifundidas (ZS) y lamelas con mayor grado de fusión (ZF). Los ensayos de nanoindentación mostraron una distribución de Weibull bimodal de sus propiedades mecánicas, la cual característica de este tipo de recubrimientos; mientras que la dureza (HV) y el módulo de elasticidad evaluados por microindentación, presentaron una distribución monomodal. Estos resultados de microindentación estuvieron influenciados por el área de contacto en las zonas indentadas en la estructura bimodal del recubrimiento. Palabras clave: Recubrimiento por plasma a partir de suspensiones (SPS), estructura, indentación, Distribución Weibull, recubrimiento 8YSZ.ABSTRACT: The study of nanostructured coatings manufactured by thermal spraying has generated a great interest in the last two decades due to their considerable improved properties especially in the physical and mechanical properties. This improvement is to reduce grain sizes of their raw materials at scales of 100-1000 times lower compared to conventional coatings (microstructured). Thus, these coatings structured at the nano and sub micrometric scale start to be used in the industrial applications and, it is essential to study their mechanical properties for certain applications. Currently, the indentation is the main technique for characterizing thin films and coatings, despite being highly influenced by the defects of the coating in the vicinity of the indentation. Nanoindentation and microindentation is presented as the best option for evaluate the mechanical behavior of nanostructured coatings. For this reason, in this work the study of the effect of the structure of the 8 mol% yttria-stabilised zirconia coating (8YSZ) manufactured by suspension plasma spraying (SPS) and the relationship with its mechanical properties (hardness and elastic modulus) measures for nanoindentation and microindentation techniques was analyzed. Analysis of the structure of the cross section of coating exhibit a bimodal structure, which is composed by a zone with semi-molten nanoparticles (ZS) and lamellaes with a higher grade of fusion (ZF). Nanoindentation tests showed a bimodal Weibull distribution of the mechanical properties (hardness and elastic modulus) which is related to the two zones (ZF and ZS) present in the coat-ing, while hardness (HV) and elastic modulus measured by microhardness, showed a monomodal distribu-tion. These results of microhardness were influenced by the contact area of the indentation in zones com-posed of the bimodal structure of the YSZ coating. Keywords: Suspension plasma spraying (SPS), structure, indentation, Weibull distribution, 8YSZ coating

The history of hydrogeology at the University of Warsaw in the 60 years of its existence

W artykule przedstawiono zwięzłą historię hydrogeologii na Uniwersytecie Warszawskim na przestrzeni ostatniego sześćdziesięciolecia oraz sylwetki najwybitniejszych uczonych ze świata hydrogeologii, związanych z Wydziałem Geologii UW. Zestawiono tytuły prac doktorskich, które odzwierciedlają różnorodność problematyki hydrogeologicznej. Przedstawiono zespoły badawcze, ich liderów oraz spektrum badań. Zamieszczono również biogramy profesorów, którzy odeszli.The paper shows a brief history of hydrogeology at the University of Warsaw over the past six decades. The profiles of leading scholars in the field of hydrogeology, associated with the Faculty of Geology, are presented. The titles for doctoral dissertations are summarized, which reflect the diversity of hydrogeological sciences. The paper presents research teams, their leaders, and the spectrum of research. It also provides biographies of professors who have passed away

Evolution of Polish hydrogeology

In Poland, hydrogeology as a separate scientific discipline came into being at the end of the 19th century. The first geologists were interested in springs, saline, mineralised waters of therapeutic use and dewatering of mines. Until World War I, in the early stages of hydrogeological developments, a different attitude towards groundwater problems was clearly notable in all three annexed Polish territories. The next stage of the development of Polish hydrogeology is dated to the years 1918-1939. In those times, the major focus of hydrogeological investigations was on building structures to extract artesian groundwater; mineral groundwater in the Polish spas; building municipal water intakes; and on Quaternary aquifers, widespread in Poland. Early hydrogeological handbooks were published at those times. The contemporary stage of Polish hydrogeology started in 1945, after World War II. In the early 1950s, the Department of Hydrogeology and Engineering Geology was established at the Central Board of Geology (CUG in Polish), which belonged to the Polish government as a separate ministry up to 1970. Hydrogeological companies with technology and development sections were founded in big cities. Nowadays, academic centres exist in Warsaw, Cracow, Wrocław, Gdańsk, Sosnowiec, Poznań, Kielce and Toruń. About 1400 persons with academic diplomas, 160 doctors and 22 professors of hydrogeology are active at present in the field of hydrogeology. The principal fields of Polish hydrogeology comprise the following: mine dewatering, recognition of groundwater resources and their protection, construction and exploitation of water intakes, hydrogeological cartography, mineral and thermal water resources, regional hydrogeology for physical planning, groundwater modelling and groundwater pollution, migration of pollutants and forecasting of groundwater changes. Up to the late eighties, political censorship was the main difficulty for the development of Polish hydrogeology, especially in publications related to sensitive information of groundwater occurrence and resources

Sintering of Fine Particles in Suspension Plasma Sprayed Coatings

Suspension plasma spraying is a process that enables the production of finely grained nanometric or submicrometric coatings. The suspensions are formulated with the use of fine powder particles in water or alcohol with some additives. Subsequently, the suspension is injected into plasma jet and the liquid additives evaporate. The remaining fine solids are molten and subsequently agglomerate or remain solid, depending on their trajectory in the plasma jet. The coating’s microstructure results from these two groups of particles arriving on a substrate or previously deposited coating. Previous experimental studies carried out for plasma sprayed titanium oxide and hydroxyapatite coatings enabled us to observe either a finely grained microstructure or, when a different suspension injection mode was used, to distinguish two zones in the microstructure. These two zones correspond to the dense zone formed from well molten particles, and the agglomerated zone formed from fine solid particles that arrive on the substrate in a solid state. The present paper focuses on the experimental and theoretical analysis of the formation process of the agglomerated zone. The experimental section establishes the heat flux supplied to the coating during deposition. In order to achieve this, calorimetric measurements were made by applying experimental conditions simulating the real coatings’ growth. The heat flux was measured to be in the range from 0.08 to 0.5 MW/m2,depending on the experimental conditions. The theoretical section analyzes the sintering during the coating’s growth, which concerns the fine particles arriving on the substrate in the solid state. The models of volume, grain boundary and surface diffusion were analyzed and adapted to the size and chemistry of the grains, temperature and time scales corresponding to the suspension plasma spraying conditions. The model of surface diffusion was found to best describe the sintering during suspension plasma spraying. The formation of necks having the relative size equal to 10% of particle diameter was found to be possible during the thermal cycles occurring at the coatings’ deposition. Transmission electron microscopic observations of the agglomerated zone hydroxyapatite coating confirm the sintering of some of the fine grains

Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying

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