纳米陶瓷烧结颗粒重排行为研究

In classic sintering theory, the contribution of particle rearrangement is limited to only ~3% compact shrinkage in early stage and the followed process is exclusively dominated by atom-diffusion mechanisms. This viewpoint has been prevailing in both academia and engineering, therefore, rather limited attention has been paid to the behaviors of particle rearrangement during ceramic sintering. However, it was found that the period validity of particle rearrangement could be intensively enhanced to ~93% of density in nanoceramic sintering process. Moreover, the intensive particle rearrangement showed strong influences on the microstructural development and sintering behaviors during high-density ranges. In present project, spark plasma sintering technique will be selected for the investigation of particle rearrangement behaviors in nanoceramic sintering using zircoina nanoceramics as examples. By special modes designing, each possible influence from electric filed, heating rate and pressure will be peeled to identify its contribution to the intensive particle rearrangement. Based on these understandings, the kinetic explanations for the intensive particle-rearrangement behaviors of nanoceramic sintering will be proposed. Furthermore, the sintering process of nanoceramics will be divided by the basic densification unit, atom and grain, by which the active stage(s) and contributions of particle rearrangement will be clearly identified. The research findings of present project will be expected to be a supplement to classic sintering theory, as well as providing inspirations for the utilization of particle-rearrangement kinetics in general nanoceramic fabrications.

经典理论认为颗粒重排在烧结中的作用仅限于初期~3%，原子扩散是后续陶瓷烧结行为的唯一主导机制。目前的研究与材料制备延续这一传统思想，对颗粒重排机制在烧结中的作用并未引起足够的重视。申请人的研究显示纳米陶瓷烧结中颗粒重排行为不仅能够延伸至~93%密度，而且对于高密度阶段烧结体微观结构调控与密实化行为有重要的影响。项目以氧化锆为研究体系，选择放电等离子烧结手段，开展纳米陶瓷烧结颗粒重排行为研究。通过模具设计，实现电场、升温速率、压力等影响因素的分离；通过明晰不同烧结工艺参数对颗粒重排行为的影响，解释纳米陶瓷烧结过程中颗粒重排异于传统理论行为的动力学成因。研究提出以晶粒与原子两种密实化基础单元为依据，对纳米陶瓷烧结进行阶段划分，明确颗粒重排机制在纳米陶瓷烧结过程中的作用阶段，以及对于烧结行为的贡献。本项目的研究对于完善普适陶瓷烧结理论，指导颗粒重排机制在广泛陶瓷制备中的应用具有重要意义。

以纳米氧化锆为研究体系，选择放电等离子烧结（Spark Plasma sintering, SPS）手段，对纳米陶瓷烧结过程中“颗粒重排”进行研究。采用综合烧结曲线（Master Sintering Curve, MSC）对不同工艺条件下的SPS过程研究的结果显示：无法用单一有效激活能数值对SPS烧结全过程进行拟合，表明SPS烧结过程存在多个密实化机理主导不同的烧结阶段。不同SPS工艺参数条件下3Y-TZP纳米陶瓷“密实化速率-相对密度”研究结果显示：在压力20~100 MPa、升温速率≥50 °C/min范围，密实速率拐点稳定出现在78±4%相对密度；并以次密度阈值提出“增强颗粒重排”作为主要密实化机理主导SPS早期烧结行为的阶段划分。通过SPS模具设计，将SPS烧结过程中对于“增强颗粒重排”可能的影响因素，如电场/等离子、升温速率、压力等因素逐一进行分离，并分别研究其对于3Y-TZP纳米陶瓷SPS烧结过程“微观结构均匀化”的贡献。在微观结构表征中引入“最大气孔尺寸”参量，通过对比分析不同工艺与参数条件下烧结体“相对密度-晶粒尺寸-最大气孔尺寸”的演变，得出结论：辅助压力的使用是SPS烧结过程能够通过“增强颗粒重排”机制实现微观结构自发均匀化的关键影响因素；并且相对传统烧结的慢速升温过程，在SPS快速升温的条件下，“增强颗粒重排”能够更加充分发挥其对于微观结构均匀化的调控作用。基于上述结果，研究以“原子”和“晶粒”两种密实化基本单位，对3Y-TZP纳米陶瓷的SPS烧结过程进行了阶段划分，明确了不同烧结阶段的主导密实化机理。