The In-situ Measurements And Densification Mechanism Of Sintering ZrO₂

One of the key factors of how to make high-powered ceramic material is the control of the sintering process. And the ultimate goal of the sintering process is being able to predict the densification process of the body under different heating scheme. This study bases on the experiences of sintering Yttria stabilized zirconia compacts fabricated by cold isostatic pressing in an in-situ measurement instrument under constant heating rate and pressureless condition, and analysis the process of Sintering densification and the grain's growing. The main contents of the research are as follows.The cold isostatic pressing of ZrO₂ were 180 Mpa, 280 Mpa, 550 Mpa. And the heating rates were 2?/min, 5?/min, 8?/min, respectively. The images were saved by the in-situ measurement instrument and processing the shrinkage data. Then we can establish the control sintering curve. we can also simplified calculation process by using VBA program to make a sintering time surface figure, and then we can predict the time needed for a certain density of sintered density, and get the MSC fitting curve.After establishing the MSC, we can obtain the sintering activation energy at 180 Mpa, 280 Mpa, 550 Mpa. They were successfully calculated to be 685.7k J/mol, 661.1 k J/mol, 652.3 k J/mol, respectively. This shows that the greater molding pressure, the lower sintering activation energy of the body, the better sintering will be get. The primary reason is the large openings are disappeared because of high pressure.To make further on the base of the control sintering curve, we extended the master sintering curve?EMSC? and successfully modeled the relationship between the temperature and the relative density in the sintering process under constant heating rate, not just to predict the ultimate density. The results show that in 180 Mpa molding pressure, the experimental data of different heating rates are very accordant to the simulated data. Besides that, in order to prove the EMSCE are accurate in any conditions, we added two simulation curves?1 ? / min with 10 ? / min? compared to the original plan, the sintering curve trends are basically identical.Non-isothermal densification process can be divided into three stages: initial, intermediate and final stages. Densification process mainly happened in the middle stage, but seldom in the initial stage and final stage. The bigger the density of green body is, the greater dense the sintered body is. This phenomenon is especially clear in the former process of sintering, to late the difference becomes smaller, the sintered density reached one point, which means they are completely density. The process of grain's growing can be divided into two stages by a density of 90%, when the body density is less than 90%, grain growth speed is slow, the pore in the body belongs to trepanning, hinder the grain's boundary to move; When body density is greater than 90%, the rapid rate of grain growth is accelerated, because the body is basic density, the pore in the body are mainly obturators, will not hinder the movement of the grain boundary, so the grain naturally began to increase.Study on the densification mechanism. On the basis of the traditional sintering theory, we used the regression analysis method, determined the densification mechanism in the process of the ZrO₂ sintering process is mainly the grain boundary diffusion.