Preparation And Mechanical Properties Of Al₂O₃ Ceramics By Hot Oscillating Pressing

High performance ceramics are widely used in industrial equipment because of their many excellent properties.However,ceramics prepared by traditional methods are far from meeting the requirements of modern industrial society.In order to make ceramic products develop towards the direction of high density,high performance and high efficiency,scholars put forward a new sintering technology of adding multiple external physical fields to the traditional sintering method of ceramic products,namely the ceramic sintering technology under the action of multiple coupled physical fields.Hot oscillating pressing is a new type of multi-field coupling sintering technology in which stress field and temperature field interact with each other.By using this sintering technology,scholars have prepared a variety of high-performance materials.In this paper,the sintering behavior and mechanical properties of alumina ceramics,which are widely used,were studied by hot oscillating pressing.The main research work is as follows:1.The densification process of hot oscillating pressing at different sintering temperatures was studied,and the densification process of hot oscillating pressing and hot pressing at 1200℃was compared.Results show that the densification process of hot oscillating pressing is faster and the densification rate is higher than that of hot pressing,because the oscillating pressure provides a greater driving force for sintering,which further promotes the rearrangement of particles in the billet,at the same time,the oscillating pressure effectively breaks the particle agglomeration phenomenon inside the blank body and shortening the material diffusion distance,it accelerates the viscous flow and diffusion creep in the middle and late stage of sintering,promotes the slip of grain boundary,and finally increases the densification rate and speeds up the densification process of the material;2.The effects of different sintering parameters（such as holding time,frequency and amplitude）on the density of alumina ceramics were studied.The frequency of 1 Hz and the amplitude of 40±5 MPa were determined to be the optimal values of the corresponding parameters,and the current hot oscillating pressing process was optimized;3.The effects of sintering parameters（sintering temperature,oscillatory pressure application stage and holding time）on the microstructure of alumina ceramics were investigated.The results of grain growth show that the grain size of HOP samples is smaller and the grain size distribution area is narrower at the same sintering temperature,which indicates that the oscillatory pressure effectively inhibits the grain growth and optimizes the microstructure.In several groups of experiments with different sintering parameters,there are more transgranular fractures in the fracture SEM of HP samples,but less such phenomena in the fracture SEM of HOP samples,indicating that the oscillatory pressure is conducive to strengthening the grain,and then improving the fracture strength of the samples;4.The grain growth kinetics of hot oscillating pressing sintered alumina ceramics was studied.The grain growth activation energy of hot oscillating pressing sintered alumina ceramics(E=547.7±8.5 kJ·mol^-1)is calculated when the grain index is n=3,which is significantly higher than the previously reported grain growth activation energy(E=443kJ·mol^-1).The results show that the oscillatory pressure increases the activation energy of grain growth of alumina ceramics,and explains the reason why the oscillatory pressure effectively inhibits grain growth from the perspective of the activation energy of grain growth;5.The effects of hot oscillating pressing and hot pressing on the sintering behavior and mechanical properties of alumina ceramics at different sintering temperatures were compared.Under the conditions of 1500℃,the properties of HOP samples are the best.The relative density of HOP samples is 99.94%,the hardness is 22±0.152 GPa,the bending strength is 400±10 MPa,and the grain size is 3.989±1.308μm;The relative density of HP sample is 99.62%,the hardness is 20.836±0.697 GPa,the bending strength is 389±11 MPa,and the grain size is 4.994±1.960μm.The results show that the oscillating pressure produces a greater driving force for sintering,which increases the densification rate,speeds up the densification process,reduces the porosity and other defects in the sample,increases the final density of the sample,and improves the mechanical properties of the sample.In addition,the oscillatory pressure increases the activation energy of grain growth of alumina ceramics,further inhibits the grain growth,promotes the grain refinement and homogenization of the samples,and improves the mechanical properties of the samples;6.The effect of oscillatory pressure on the mechanical properties of alumina ceramics was studied,and the relationship between microstructure and mechanical properties was established.The results show that the oscillatory pressure in a single sintering stage of the sample,the oscillatory pressure in the late sintering stage of the sample to improve the mechanical properties of the largest,indicating that the oscillatory pressure is conducive to the elimination of the colsed pores and densification in the late sintering stage.The samples subjected to oscillatory pressure throughout the sintering stage have the best mechanical properties,which indicates that sintering is a continuous process and the resulting chain effect will further improve the properties of the samples.The Weibull modulus of bending strength of HP,HOP-1300 and HOP-ALL samples were calculated to be 9.36,15.04 and15.52,respectively.The results show that HOP-ALL has the best reliability because of the smallest average grain size,the lowest porosity and the most uniform microstructure.