Microstructure and indentation mechanical properties of YSZ nanostructured coatings obtained by suspension plasma spraying

[EN] A commercial nanosuspension of yttria-stabilised zirconia (YSZ) was successfully deposited on austenitic stainless steel substrate by suspension plasma spraying technique (SPS). A SG-100 torch with internal radial injection was used for the spraying. The pneumatic system transported the feed suspension from the containers to the plasma torch. In order to study the effect of the spraying parameters, a factorial model was used to design the experiments, changing both spraying translation speed and suspension flow rate. The coating microstructure was characterised by FEG-SEM. All coatings displayed a two-zone microstructure formed by nanometre-sized particles surrounded by fully molten areas. Moreover, crystalline phases were determined by XRD and Raman spectroscopy. Mechanical properties were also determined using nanoindentation technique. Nanoindentation tests showed a bimodal distribution of the mechanical properties (hardness and Young's modulus) which is related to the two zones (molten and partially molten) present in the coatings. (C) 2012 Elsevier B.V. All rights reserved.This work has been supported by the Spanish Ministry of Science and Innovation (project MAT2009-14144-C03) and the Research Promotion Plan of the Universitat Jaume I, action 2.1 (ref. E-2011-05) and action 3.1 (ref. PREDOC/2009/10). The authors are grateful to Leszek Łatka for his help in plasma spray experiments.Carpio, P.; Rayón Encinas, E.; Pawlowski, L.; Cattini, A.; Benavente Martínez, R.; Bannier, E.; Salvador Moya, MD.... (2013). Microstructure and indentation mechanical properties of YSZ nanostructured coatings obtained by suspension plasma spraying. Surface and Coatings Technology. 220:237-243. https://doi.org/10.1016/j.surfcoat.2012.09.047S23724322

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

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