Shrinkaging Behaviour And Its Mechanism Of Zirconia Ceramic During The Sintering

Due to the high hardness, poor tenacity and the difficulty of processing for ceramics, near net shape has always been one of the hot points for the research work of material science workers. However, in the process of experiment and production, it is common that anisotropic shrink occur in the green body during sintering. Previous works mainly focused on the influence of powder shape, molding craft and sintering environment on the dimensional accuracy of the green body. But the influence of the shape and dimension of the specimens or green bodies on sintering deformation has seldom been mentioned. Therefore, in this thesis, we approach this issue from a three-dimensional vision. In order to thoroughly understand the influence of shape and dimension of green bodies on sintering deformation, one-dimensional (thin rod shape), two-dimensional (lamelliform shape) as well as three dimensional (rectangle and complicated shape) specimens are systematically studied. The main research achievements are as follows:The concept of anisotropic shrinkage factor is introduced to quantitatively characterize the shrinkaging behaviour of the ceramics. The anisotropic shrinage factor M=the shrinkage of the length/the shrinkage of the diameter (or the width or height) during the sintering.In the research of one-dimensional (clavate) specimens, the shrinkage of the length is found to be greater than that of the diameter, and the shrinkage monotone increases with the increase of the length-diameter ratio. A linear relationship is found between the length-diameter ratio, the shrinkage and the shrink anisotropic factor. The higher the temperature, the greater the shrinkage and the shrink anisotropic factor. The phenomenon of the anisotropic shrink of the clavate specimen is attributed to the influence of the interface energy, but the process of densifying and nodulizing can accelerate it as well.In the research of two-dimensional specimens, in the premise of avoiding to the largest extent the sintering anisotropic shrink created by other factors such as the powder particles and the technological parameters, the behavior of anisotropic shrink becomes more obvious with the increase of the length-width ratio. Besides, the shrinkage of solid specimens is bigger than that of the specimens with holes inside, and the shrinkage of the holes is bigger than that of the green body. When the diameter is equal to the length, the shrinkage of the round holes is bigger than that of the square holes. It is found that smaller holes have bigger shrinkage, which is also attributed to the interface energy.In the research of three-dimensional specimens of rectangular bars, it is found that the shrinkage of the length is the greatest, the shrinkage of the height is the smallest and that of the width is between the two above. Both the shrinkage and the shrink anisotropic factor are linear to the length-width ratio and the length-height ratio. Besides, in the case of the same length-width ratio and length-height ratio, the higher the sintering temperature, the greater the shrinkage and the shrink anisotropic factor. By comparing the shrink behavior of MSZ and YSZ, it is found that their trend of sintering anisotropic shrink is in accordance with each other. However, because of the difference of the property, they are found to have different shrinkage and shrink anisotropic factors. For the specimens with the complicated shape of switch box which contains holes, the sintering anisotropic shrink is found in the whole specimen and the shrinkage of the length is bigger than that of the width and thickness. Besides, the shrinkage of the holes inside is bigger than that of the specimens. The smaller the holes, the bigger the shrinkage. The interface energy and the interface tension are important reasons that lead to the anisotropic shrinkage.By utilizing the picture processing and data mining technics, the arrangement and distribution state of the powder particles in the curtain coating paste can be studied quantitatively. Especially, we intuitively described the arrangement rules of the powder particles by using the particle morphology ratio and the distribution diagram of the angle of orientation. For the specimens prepared using nonspherical micron powder and nano powder with the same length-width ratio, the former is found to have more obvious sintering anisotropic shrink. In addition to the factor of length-width ratio, the arrangement state of the powder particles is another important reason that give rise to the anisotropic shrinkage during the sintering.