快速升温对材料烧结和合成的影响研究
发布时间：2018-11-20 20:19
【摘要】：新型的快速升温热处理技术(放电等离子烧结(SPS),“闪烧”Flash-Sintering等)在材料成型、烧结、合成等方面表现出了诸多不同于传统高温热处理技术的特性,如降低烧结温度、缩短烧结/合成时间、细化晶粒和改善烧结体性能等。但当前较多学者对于上述特性的内在规律存在较多的争议,这严重地制约了上述技术的发展。从大量的研究结果和理论推测看,不同于传统加热方式的快速升温过程可能是导致上述新特性出现的关键性因素。快速升温可影响、改变材料在烧结致密化、合成过程的热动力学,从而影响材料组成、结构及性能。为了验证这一推测,本课题利用多种工艺,实现了不同升温速度的快速热处理工艺,研究和揭示了升温速度对几类典型材料热处理动力学过程的影响。主要研究结果如下:以氧化铝为烧结致密化对象,研究了升温快慢对烧结致密化和晶粒生长热动力学的影响。结果发现:在无压条件下,快速升温过程能极大地抑制传统烧结初期的表面扩散所导致的颈部生长及烧结激活能的低效率损耗等,从而使坯体在烧结中期保留了较强的烧结活性和物质扩散速度,提高了烧结致密化速率,但这种快速物质扩散也导致了烧结过程中晶粒的快速生长,晶粒尺寸分布变宽;在压力作用下,颗粒的塑性流动和重排致密化速率有明显提高,并明显地抑制了快速升温对致密化、晶粒长大规律的促进作用。同时,我们探索了高温、快速升温条件下的无压氧化铝烧结致密化技术。结果显示,高的烧结温度和升温速率能进一步促进、放大升温速度对致密化和晶粒生长的促进作用。在最高温度为1750℃,全过程3min内可实现氧化铝的完全致密化,这为陶瓷材料的超快速致密化烧结技术提供了基础。以钛酸钡陶瓷和莫来石为对象,研究了快速升温热处理过程对材料在高温下的相变和化学反应动力学的影响。结果发现,较快的升温速度可抑制高温热处理中钛酸钡从低温立方相向高温六方相的转变。当升温速度达到一定程度后,合成产物为富铝莫来石、且晶体形貌出现明显变化,升温速度改变了晶体的形核-生长动力学被认为是出现上述特性的主要原因。
[Abstract]:The new rapid heating treatment technology (SPS), "flash sintering" Flash-Sintering et al.) shows many characteristics different from the traditional high temperature heat treatment technology in material forming, sintering and synthesis, such as lowering the sintering temperature. The sintering / synthesis time is shortened, the grain size is refined and the properties of the sintered body are improved. However, there are many controversies about the inherent laws of the above characteristics, which seriously restrict the development of the above technology. From a large number of research results and theoretical speculation, the rapid heating process different from the traditional heating mode may be the key factor leading to the emergence of the new characteristics. The rapid heating can affect the sintering densification of the material and the thermal kinetics of the synthesis process, thus affecting the composition, structure and properties of the material. In order to verify this hypothesis, the rapid heat treatment process with different heating rates has been realized by using a variety of processes, and the effect of the heating rate on the heat treatment kinetics of several typical materials has been studied and revealed. The main results are as follows: taking alumina as the sintering densification object, the effect of the temperature rise rate on the sintering densification and the thermal kinetics of grain growth was studied. The results show that under the condition of no pressure, the rapid heating process can greatly restrain the neck growth caused by the surface diffusion in the early stage of traditional sintering and the low efficiency loss of the activation energy of sintering, etc. Thus, during the middle stage of sintering, the billet retained strong sintering activity and material diffusion speed, and increased the sintering densification rate, but this rapid material diffusion also led to the rapid growth of grain size distribution in the sintering process. Under pressure, the plastic flow and rearrangement densification rate of particles are obviously increased, and the accelerating effect of rapid heating on densification and grain growth is obviously inhibited. At the same time, we have explored the sintering densification technology of pressureless alumina under the condition of high temperature and rapid heating. The results show that high sintering temperature and heating rate can further promote the densification and grain growth. The complete densification of alumina can be realized in the whole process of 3min at the maximum temperature of 1750 鈩，
本文编号：2345901
[Abstract]:The new rapid heating treatment technology (SPS), "flash sintering" Flash-Sintering et al.) shows many characteristics different from the traditional high temperature heat treatment technology in material forming, sintering and synthesis, such as lowering the sintering temperature. The sintering / synthesis time is shortened, the grain size is refined and the properties of the sintered body are improved. However, there are many controversies about the inherent laws of the above characteristics, which seriously restrict the development of the above technology. From a large number of research results and theoretical speculation, the rapid heating process different from the traditional heating mode may be the key factor leading to the emergence of the new characteristics. The rapid heating can affect the sintering densification of the material and the thermal kinetics of the synthesis process, thus affecting the composition, structure and properties of the material. In order to verify this hypothesis, the rapid heat treatment process with different heating rates has been realized by using a variety of processes, and the effect of the heating rate on the heat treatment kinetics of several typical materials has been studied and revealed. The main results are as follows: taking alumina as the sintering densification object, the effect of the temperature rise rate on the sintering densification and the thermal kinetics of grain growth was studied. The results show that under the condition of no pressure, the rapid heating process can greatly restrain the neck growth caused by the surface diffusion in the early stage of traditional sintering and the low efficiency loss of the activation energy of sintering, etc. Thus, during the middle stage of sintering, the billet retained strong sintering activity and material diffusion speed, and increased the sintering densification rate, but this rapid material diffusion also led to the rapid growth of grain size distribution in the sintering process. Under pressure, the plastic flow and rearrangement densification rate of particles are obviously increased, and the accelerating effect of rapid heating on densification and grain growth is obviously inhibited. At the same time, we have explored the sintering densification technology of pressureless alumina under the condition of high temperature and rapid heating. The results show that high sintering temperature and heating rate can further promote the densification and grain growth. The complete densification of alumina can be realized in the whole process of 3min at the maximum temperature of 1750 鈩，
本文编号：2345901
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