【摘要】：新型的快速升溫?zé)崽幚砑夹g(shù)(放電等離子燒結(jié)(SPS),“閃燒”Flash-Sintering等)在材料成型、燒結(jié)、合成等方面表現(xiàn)出了諸多不同于傳統(tǒng)高溫?zé)崽幚砑夹g(shù)的特性,如降低燒結(jié)溫度、縮短燒結(jié)/合成時間、細(xì)化晶粒和改善燒結(jié)體性能等。但當(dāng)前較多學(xué)者對于上述特性的內(nèi)在規(guī)律存在較多的爭議,這嚴(yán)重地制約了上述技術(shù)的發(fā)展。從大量的研究結(jié)果和理論推測看,不同于傳統(tǒng)加熱方式的快速升溫過程可能是導(dǎo)致上述新特性出現(xiàn)的關(guān)鍵性因素。快速升溫可影響、改變材料在燒結(jié)致密化、合成過程的熱動力學(xué),從而影響材料組成、結(jié)構(gòu)及性能。為了驗證這一推測,本課題利用多種工藝,實(shí)現(xiàn)了不同升溫速度的快速熱處理工藝,研究和揭示了升溫速度對幾類典型材料熱處理動力學(xué)過程的影響。主要研究結(jié)果如下:以氧化鋁為燒結(jié)致密化對象,研究了升溫快慢對燒結(jié)致密化和晶粒生長熱動力學(xué)的影響。結(jié)果發(fā)現(xiàn):在無壓條件下,快速升溫過程能極大地抑制傳統(tǒng)燒結(jié)初期的表面擴(kuò)散所導(dǎo)致的頸部生長及燒結(jié)激活能的低效率損耗等,從而使坯體在燒結(jié)中期保留了較強(qiáng)的燒結(jié)活性和物質(zhì)擴(kuò)散速度,提高了燒結(jié)致密化速率,但這種快速物質(zhì)擴(kuò)散也導(dǎo)致了燒結(jié)過程中晶粒的快速生長,晶粒尺寸分布變寬;在壓力作用下,顆粒的塑性流動和重排致密化速率有明顯提高,并明顯地抑制了快速升溫對致密化、晶粒長大規(guī)律的促進(jìn)作用。同時,我們探索了高溫、快速升溫條件下的無壓氧化鋁燒結(jié)致密化技術(shù)。結(jié)果顯示,高的燒結(jié)溫度和升溫速率能進(jìn)一步促進(jìn)、放大升溫速度對致密化和晶粒生長的促進(jìn)作用。在最高溫度為1750℃,全過程3min內(nèi)可實(shí)現(xiàn)氧化鋁的完全致密化,這為陶瓷材料的超快速致密化燒結(jié)技術(shù)提供了基礎(chǔ)。以鈦酸鋇陶瓷和莫來石為對象,研究了快速升溫?zé)崽幚磉^程對材料在高溫下的相變和化學(xué)反應(yīng)動力學(xué)的影響。結(jié)果發(fā)現(xiàn),較快的升溫速度可抑制高溫?zé)崽幚碇锈佀徜^從低溫立方相向高溫六方相的轉(zhuǎn)變。當(dāng)升溫速度達(dá)到一定程度后,合成產(chǎn)物為富鋁莫來石、且晶體形貌出現(xiàn)明顯變化,升溫速度改變了晶體的形核-生長動力學(xué)被認(rèn)為是出現(xiàn)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，

本文編號：2345901