Wettability, surface tension, and reactivity of the molten manganese/zirconia-yttria ceramic system
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I.
INTRODUCTION
PLASMA-SPRAYED ceramic coatings are employed as the surface protection films of metallic materials, which are used under severe environments such as high temperature and corrosion. The corrosion resistance and the mechanical strength decrease due to the presence of open pores, which exist in ceramic coatings. One approach to improving the performance of ceramic coatings is to eliminate the pores by infiltrating molten metal. Infiltration is governed by the wettability of ceramic coatings by molten metal and the surface tension of molten metal. It is also important to know reactivity, because the reaction between ceramics and molten metal exerts an influence on wettability. Nevertheless, little research has been done on interfacial phenomena and reactions between molten manganese and the zirconia ceramics. Furthermore, there are no data on the wettability of zirconia ceramics having a smooth surface by molten manganese. In this article, the wettability and reactivity of the molten manganese/zirconia ceramics system and the surface tension of molten manganese are studied as contributing to making ceramic coatings dense. II.
EXPERIMENTS
A. Materials Ceramic substrates and metallic manganese samples were prepared as follows. Zirconia substrates containing Y2O3 of 3 or 8 mol pct were sintered at 1673 K. It was confirmed from X-ray diffractometer (XRD) analysis that the ZrO2-3 mol pct Y2O3 and ZrO2-8 mol pct Y2O3 substrates were composed of tetragonal and cubic structures, respectively. These substrates were processed to be 17 mm in length and width and 3 mm
N. SHINOZAKI, Assistant Professor, and K. MUKAI, Professor, are with the Department of Materials Science and Engineering, Faculty of Engineering, Kyushu Institute of Technology, Kita-kyushu, 804, Japan. M. SONODA, formerly Graduate Student, Department of Materials Science and Engineering, Kyushu Institute of Technology, is Engineer with Sankyu Co. Ltd., Kita-kyushu, 804, Japan. Manuscript submitted January 27, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
in thickness. The surfaces of the substrates were polished with 1500 emery paper. Electrolytic manganese of 99.9 mass pct purity was processed to a hexagonal plate of 0.4 g with 1-mm thickness, and the surfaces were polished. Five strips of manganese were used in each experiment. B. Experimental Procedure A fundamental measure of wettability is the contact angle. The contact angle between molten manganese and zirconia substrate and the surface tension of molten manganese on the substrate were measured by the sessile drop method. A schematic view of the apparatus used for the experiments is shown in Figure 1. At first, five strips of manganese were piled on a zirconia substrate, and they were set in a reaction tube made of alumina. The tube was evacuated and then argon gas was supplied. Argon gas was supplied continuously during the process of experimentation. Zirconia substrate and manganese samples were heated at a rate of 500 K/h and were maintained at a temperature of 1573 K for up to 3 h
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