Boldin Maksim S, Popov Alexander A, Lantsev Evgeni A, Nokhrin Aleksey V, Chuvil'deev Vladimir N
Materials Science Department, Research and Development Institute of Physics and Technology, National Research Lobachevsky State University of Nizhny Novgorod, Gagarin Ave. 23/3, 603022 Nizhny Novgorod, Russia.
Materials (Basel). 2022 Mar 15;15(6):2167. doi: 10.3390/ma15062167.
The article presents the results of the investigation of the mechanism of the densification behavior of alumina-based ceramics during spark plasma sintering. The role of the heating rates and additives were investigated. The first (initial) stage of sintering was investigated by the Young-Cutler model. The second (intermediate) stage of sintering was investigated as a process of plastic deformation of a porous body under external pressure. It was shown that, at the initial stage, the formation of necks between the particles is controlled by grain boundary diffusion (the activation energy is ≈ 20 kT). At this stage, accommodation of the shape of the alumina particles is also occurring (an increase in the packing density). The accommodation process facilitates the shrinkage of the powder, which is reflected in a decrease in the effective activation energy of shrinkage at low heating rates (10 °C/min) to ≈ 17 kT. At heating rates exceeding 10 °C/min, the intensity of the processes of accommodation of alumina particles turns out to be much slower than the existing diffusion processes of growth of necks between the alumina particles. It was shown that the grain boundary sliding mechanism that occurs in the second stage of sintering can play a decisive role under conditions of spark plasma sintering with a high heating rate. The found value of the activation energy at the second stage of sintering is also close to the activation energy of grain-boundary diffusion of alumina ( ≈ 20 kT). The influences of the second phase particles of MgO, TiO, and ZrO on densification behavior of alumina-based ceramics were investigated. Since at the first stage of sintering the densification relates with the formation of necks between the particles of alumina, the additives (0.5% vol) have no noticeable effect on this process. It was also shown that the second phase particles which are located at the grain boundaries of alumina are not involved in the slip process during the second sintering stage. Analysis shows that additives act only in the final (third) stage of spark plasma sintering of alumina.
本文介绍了对氧化铝基陶瓷在放电等离子烧结过程中致密化行为机制的研究结果。研究了加热速率和添加剂的作用。烧结的第一（初始）阶段采用Young-Cutler模型进行研究。烧结的第二（中间）阶段作为多孔体在外部压力下的塑性变形过程进行研究。结果表明，在初始阶段，颗粒间颈部的形成受晶界扩散控制（激活能约为20kT）。在此阶段，氧化铝颗粒的形状也在调整（堆积密度增加）。这种调整过程促进了粉末的收缩，这在低加热速率（10℃/min）下收缩有效激活能降至约17kT中得到体现。当加热速率超过10℃/min时，氧化铝颗粒的调整过程强度比氧化铝颗粒间颈部生长的现有扩散过程慢得多。结果表明，在高加热速率的放电等离子烧结条件下，烧结第二阶段发生的晶界滑动机制可能起决定性作用。在烧结第二阶段发现的激活能值也接近氧化铝晶界扩散的激活能（约20kT）。研究了MgO、TiO和ZrO第二相颗粒对氧化铝基陶瓷致密化行为的影响。由于在烧结的第一阶段致密化与氧化铝颗粒间颈部的形成有关，添加剂（0.5%体积分数）对该过程没有明显影响。还表明，位于氧化铝晶界处的第二相颗粒在第二烧结阶段不参与滑动过程。分析表明，添加剂仅在氧化铝放电等离子烧结的最终（第三）阶段起作用。
