高致密度氮化硼及其复相陶瓷的振荡压力烧结及性能研究

The wide application of boron nitride (BN) is limited because of its difficult to densification sintering. And due to limitations in the existing sintering technologies, it is difficult to obtain BN and its multiphase ceramics with submicron or nano-scale crystals and high density (nearly pore-free). Recent some studies have found that the introduction of dynamic oscillatory pressure could effectively eliminate pores and inhibit grain growth, and the density and flexure strength were also significantly improved. Based on this novel idea for sintering, in this project, an oscillatory pressure sintering (OPS) technology is applied to densification sintering of BN and its multiphase ceramics. The effects of oscillatory pressure and frequency on the rearrangement of BN particles, the grain movement, grain boundary migration and pores removal are systematically investigated. The densification route of BN powders is obtained from the measuring-displacement system. Such route, as well as the variation of grain size, can provide us with the Master Sintering Curve (MSC) and kinetic Windows of BN ceramics sintered by OPS. The effects of pressure value and frequency on the microstructure and mechanical behaviors of BN and its multiphase ceramics are investigated in detail, so as to achieve optimized technological parameters. Therefore, this work can reveal the sintering mechanisms of BN and its multiphase ceramics in the process of OPS, and builds the basis for preparing advanced BN and its multiphase ceramics with high density, fine grains, little defects and excellent strength.

氮化硼（BN）难以致密化烧结是限制其广泛应用的关键问题之一，而现有的烧结技术尚难以获得高致密度（几乎无气孔）的亚微米或纳米尺度的BN及其复相陶瓷材料。最近一些研究发现，陶瓷粉末烧结过程中引入动态振荡压力可显著消除陶瓷内气孔等缺陷且细化晶粒，致密度和抗弯强度均大幅提高。基于这一新的烧结思路，本项目将动态振荡压力烧结新技术应用于BN及其复相陶瓷的致密化烧结，系统深入研究振荡压力和频率对BN粉末颗粒的重排、致密化过程中晶粒移动与晶界的迁移以及封闭气孔的排除作用机制；采用实时位移检测系统测量BN粉体的致密化曲线，结合晶粒尺寸变化，得到振荡压力烧结BN陶瓷的MSC曲线和烧结动力学窗口；研究振荡压力振幅、频率对BN及其复相陶瓷微观结构与宏观性能的作用规律，优化烧结工艺参数。本项目的实施，可以深入揭示BN陶瓷振荡压力烧结规律和烧结机理，为高致密度、细晶粒、低缺陷、高强度BN及其复相陶瓷的制备奠定基础。

随着冶金、化工、宇航和新能源等现代化工业和尖端技术的迅猛发展，越来越多陶瓷材料服役于高温等极端环境中，迫切需要发展综合性能优异的高温陶瓷材料。而在这些研究的高温陶瓷材料中，六方氮化硼陶瓷因具有较高的使用温度及较好的综合性能，使氮化硼及其复相陶瓷已被广泛应用在很多耐高温领域。但因氮化硼晶粒为片状，导致氮化硼及其复相陶瓷难以烧结高度致密化，从而极大限制了它的广泛应用。并且目前采用的静态、恒定压力烧结难以实现h-BN及其复相陶瓷的高度致密化。为解决氮化硼及其复相陶瓷高度致密化的难题，本项目采用新型振荡压力烧结，系统研究了振荡压力烧结h-BN及其复相陶瓷的致密化过程及机理，振荡压力下烧结参数的影响，振荡压力烧结h-BN及其复相陶瓷的微观结构，以及振荡压力烧结h-BN及其复相陶瓷的力学性能。. 其中比较突出、具有代表性的成果包括：(1) 相比于热压烧结，采用振荡压力烧结制备的h-BN陶瓷能更有效促进h-BN陶瓷晶粒的定向生长，提高晶粒的定向排列程度，促进晶粒的定向偏转和排列。(2) 振荡压力烧结制备的h-BN陶瓷具有较高的力学性能，相比热压烧结，其抗弯强度提高了约40%，而且烧结过程中振荡压力的引入明显提高了材料致密度、断裂可靠性和热导率。(3) 振荡压力烧结工艺中烧结温度、保温时间、振荡压力振幅以及频率都会影响h-BN及其复相陶瓷的致密化及力学性能，振荡压力的引入对致密化进程产生了显著的活化效果，并明显抑制了晶粒生长。且振荡压力有助于强化晶粒强度，促进气孔缺陷的排出，进而提高力学性能。 (4) 振荡压力烧结制备的Si3N4/h-BN复相陶瓷致密度明显高于常规热压烧结，且与单相h-BN陶瓷相比，添加20vol% Si3N4的Si3N4/h-BN复相陶瓷的抗弯强度提高约2.3倍，断裂韧性提高约1.7倍。项目执行以来，在本领域国内外学术期刊上已发表SCI/EI收录的文章16篇，核心期刊1篇，申请国家发明专利2项。上述研究工作所取得的研究结果能够为h-BN及其复相陶瓷在耐高温领域的应用提供一定的基础数据和关键技术，具有一定的科学意义和实际应用价值。