GPa量级压力下陶瓷的致密化机理与结构微观动力学

GPa-scale ultrahigh pressure sintering technology is one of the most important research scopes for advanced new ceramic materials. It can not only resolve the contradiction between high density and fine grain structure during ceramic sintering, but also lead to unique microstructure and fantastic properties. However, the lack of deep study on the densification mechanisms and microstructure evolution behaviors during ultrahigh pressure sintering of ceramics will inhibit the development of new materials. In traditional sintering theory, atomic diffusion is still considered as the dominate densification mechanism in pressure sintering. But in the previous study, we found that the plastic deformation and creep etc. caused by high pressure could dramatically improve the densification. The related unique microstructure could contribute to the high properties such as hardness and strength. Based on the new phenomenon, in this subject we propose to systematically study the densification behavior, microstructure evolution and properties of typical ceramics under different pressure scales from 0 MPa to several GPa. Combined with the modeling results, the dominate densification mechanism of ultrahigh pressure and high temperature sintering technology, and the relationship between dominate sintering mechanism and properties will be well revealed. It is believed that this subject will accelerate the developments of new sintering theory, advanced technology and high-performance materials.

GPa量级压力的极端条件不仅可以解决陶瓷材料高密实度与细晶粒不能兼顾的难题，还赋予其独特的显微结构和超常的性能,是先进陶瓷新材料发展的重要方向。但目前对于GPa量级压力下陶瓷的致密化机理和结构微观动力学研究还较少且缺乏深度。传统理论认为在压力烧结中扩散依然是陶瓷烧结的主导机制，但在前期的工作中我们发现由压力所引起的塑性变形、蠕变等机制对于陶瓷致密化有显著的贡献，出现的特殊显微结构对材料硬度、强度等性能的提高有积极的作用。针对这些新现象，本项目提出利用GPa量级超高压（大腔体压机）、百MPa量级高压（热等静压）和无压烧结等手段，将塑性变形、原子扩散等致密化机理进行分别强化，通过研究几种典型陶瓷材料的致密化行为、结构演化规律和性能特性，结合烧结模型和动力学计算，来揭示GPa量级压力条件下陶瓷烧结机理本质，并建立烧结机理与产品性能之间的关系，在陶瓷烧结理论方面取得进展，促进新技术和新材料的发展。

传统无压烧结陶瓷材料通过原子扩散实现粉体的致密化，但在烧结末期晶粒会不可避免地出现长大现象，这会降低陶瓷材料的力学性能。GPa量级超高压烧结技术不仅可以解决传统无压烧结过程中结构陶瓷晶粒长大、产生晶内孔以及不能实现完全致密化等难题，也能够通过激活塑性变形致密化机制，赋予陶瓷材料独特的显微结构和优异性能。本项目对比研究了GPa量级超高压、百MPa量级高压以及传统无压烧结技术中特种陶瓷的致密化行为、显微结构和性能演化规律，探索了烧结机理，建立了烧结机理与材料性能之间的关系，取得了系列成果。选取氧化物、碳化物陶瓷作为研究对象，采用百MPa高压，在相对较低的温度下烧结出完全致密且晶粒有限长大的陶瓷材料。对比了微观结构演化规律、晶界能和内应力相较于无压烧结的变化。通过GPa量级超高压技术，制备了致密的硼化物、碳化物超高熔点陶瓷，研究了极端烧结条件下的陶瓷致密化机制及其对陶瓷烧结的促进作用，系统性测试和表征了超高压制备的陶瓷材料内部的微观结构、晶界、晶粒大小和综合性能。从微观尺度描述了超高压烧结陶瓷材料的结构与性能之间的关系，探讨陶瓷材料在超高压领域烧结的实用性和科学性。本项目的研究成果，有望促进和引导高性能结构陶瓷及其烧结新技术的新发展。