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Low-temperature sintering 8YSZ microstructure and mechanical properties of

Author: GuoYanJun
Tutor: ZhouHongMing
School: Central South University
Course: Materials Science
Keywords: 8YSZ low-temperature sintering mechanical properties MnO2 TiO2 CuO
CLC: TF046.4
Type: Master's thesis
Year: 2011
Downloads: 90
Quote: 0
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Abstract


As 8 wt.%Y2O3 stablized ZrO2 (8YSZ) has low thermal conductivity, excellent oxidation resistance and good michanical properties, it was widely used in thermal barrier coatings. Electrophoretic deposition and slurry spraying can be used to prepare the 8YSZ thermal barrier coatings, because they have many advantages, the chemical composition and thickness of the coatings can be controlled accurately, low limitation in shape, gently preparation conditions, cheap equipment equipment. Now they have been become a hot research. Recently, a key problem that need to solve for these new preparation techniques is the sintering of 8YSZ, because the sintering temperature of ZrO2 is high, up to more than 1400℃, the sintering temperature is so high that the metal matrix can not stand. So lowering the sintering temperature of 8YSZ is very essential.This paper used 8YSZ as the of research object, the author added sintering aid to low the sintering temperature. Archimedes principle, hardness-testing, devices metal lographic microscope and universal-testing machine employed to measure the relative density, hardness bending strength and fracture toughness of the sintered bulk. SEM, EDS and XRD were also used to analyze the crystallographic phase, microstructure of the sintered bulk. The research content and conclusion are as follows:(1) MnO2 can lower sintering temperature of 8YSZ effectively, the relative density of sintered samples increase as the content of MnO2 increases, the best sintering ability gains when the composition is 8YSZ+3%MnO2, the relative density up to 98.6% when sintering condition is 1300℃,4h, the relative density of undoped sample is only 62.5%. When sintering aid content reaching 5%, the relative density decreases a bit. The relative density of the sintered samples increase as temperature rises; when the sintering temperature is 1300℃, the relative density of 8YSZ+3%MnO2 increase as sintering time increases. The change pattern of the hardness of sintered samples is the same as relative density in the experiment. When the aid content is less than or equal to 3%, the flexural strength of sintered samples increase as the MnO2 content increases and temperature rises. When the aid content more than 3%; the flexural strength of the sintered increase first and then drop when the sintering temperature up to 1400℃. The flexural strength of 8YSZ+3%MnO2 increase as sintering time increases. The change pattern of the fracture toughness of sintered samples is the same as flexural strength in the experiment.(2) The sintering mechanism of MnO2 promote sintering process of 8YSZ was discussed in this paper. The sintering temperature of 8YSZ lowered with MnO2 adding as sintering aid, because solid solution generates as variety valence Mn cation substitute Zr4+, which results crystal lattice distortion, and also many vacancy and extra electro emerge, all this above activate the lattice, lower the activition energy. So the diffuse of granule in the process become faster, the sintering temperature become lower.(3) MnO2-TiO2 can lower sintering temperature of 8YSZ effectively. When used MnO2-TiO2 as sintering aid, the relative density of sintered samples increase as sintering temperature rises, the best sintering ability gains when the composition is 8YSZ+3%MnO2 and 8YSZ+ 3%MnO2+0.5%TiO2. the relative density of 8YSZ+3%MnO2+0.5%TiO2 up to 95% when sintering condition is 1300℃,4h. The relative density of sintered samples decrease as the content of TiO2 increases; when the sintering temperature is 1300℃, the relative density of 8YSZ+3%MnO2+0.5%TiO2 increase as sintering time increases. The change pattern of the hardness, flexural strength and fracture toughness of sintered samples is the same as relative density in the experiment.(4) The sintering mechanism of MnO2-TiO2 promote sintering process of 8YSZ was discussed in this paper. Solid solution generates as variety of Mn valence and Ti valence substitute Zr4+, hich results crystal lattice distortion, and also many vacancy and extra electro emerge, all this above activate the lattice, lower the activition energy. MnO2-TiO2 will also form liquid phase in the process of sintering. All this above two will lower the sintering temperature of 8YSZ. (5) CuO-16.7%TiO2 can lower sintering temperature of 8YSZ effectively. When used CuO-16.7%TiO2 as sintering aid, the relative density of sintered samples increase as sintering temperature rises, the best sintering ability gains when the composition is 8YSZ +0.5%(CuO-16.7%Ti02). The relative density of sintered samples decrease as sintering aid content increase; when the sintering temperature is 1300℃, the relative density of 8YSZ+0.5%(CuO-16.7%Ti02) increase as sintering time increases..The change pattern of the hardness, flexural strength and fracture toughness of sintered samples is the same as relative density in the experiment.(6) The sintering mechanism of CuO-16.7%TiO2 promoting sintering process of 8YSZ was discussed in this paper. A eutectic point exists on the 919℃when the composition is CuO-16.7%TiO2, so liquid phase appear in the process of sintering. Because appearance of liquid phase, there will form large capilarity force, which results granuler slip and rearrangement, the ZrO2 granuler can also realize rapid diffusition through dissolution-precipation, the sintering temperature lowered through this mechanism.

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CLC: > Industrial Technology > Metallurgical Industry > General issues > Smelting of raw materials and ore pretreatment > Ore pretreatment, sintered pellets > Sintering
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