振荡压力烧结法制备高性能结构陶瓷及烧结机理研究

With the advancement of major projects and extreme serving conditions, the mechanical performances of structural ceramics, such as strength, toughness and reliability, are becoming daily more important. Here, a novel oscillatory pressure sintering (OPS) was proposed, by applying an oscillatory pressure with controllable value and frequency during sintering. In this work, we chosen zirconia and silicon nitride as object, and investigated their densification, grain growth, defect removal, strength and toughness under OPS process. The densification route was obtained from the measuring-displacement system. Such route, as well as the variation of grain size, could provide us with the Master Sintering Curve (MSC) and kinetic Windows of OPS. The effect of pressure value and frequency on the microstructure and mechanical behaviors was investigated in detail, so as to achieve optimized technological parameters. Thus, this work could reveal the sintering mechanisms of OPS process, and build the basis for preparing advanced structure ceramics with high density, fine grains, little defects and excellent strength.

本项目针对重大工程和极端环境对结构陶瓷强度、韧性和可靠性提出的日益苛刻的要求，拟在陶瓷材料烧结过程中施加振幅与频率可控的振荡压力，发展全新的振荡压力烧结法。区别于传统的无压烧结、热压烧结，振荡压力烧结法提供较高的烧结驱动力：(1)提高颗粒堆积密度，缩短物质扩散、迁移路径；(2)赋予材料多种烧结机制，加速致密化进程；(3)促进晶界处闭气孔的排出，降低缺陷浓度。本课题拟选择典型的固相烧结陶瓷氧化锆、液相烧结陶瓷氮化硅为研究对象，开展振荡压力烧结材料致密化进程、晶粒生长、缺陷消除、强韧化等的研究：采用实时位移检测系统测量粉体的致密化曲线，结合材料的晶粒尺寸变化，得到振荡压力烧结陶瓷的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，可以深入揭示振荡压力烧结规律和烧结机理，为高密度、细晶粒、低缺陷、高强度结构陶瓷的制备奠定基础。

结构陶瓷的烧结致密化是制备高性能陶瓷部件的关键技术之一，也是目前材料界研究的前沿和热点。目前常用的烧结技术（HP、SPS、FAST等），尚无法满足诸多重大工程和关键技术对低缺陷、高强度、高可靠性陶瓷部件的需求。针对这一技术瓶颈，我们提出了振荡压力烧结（Oscillatory Pressure Sintering, OPS；Vibration-assisted Hot Pressing, VAHP）新思想，通过对待烧粉体\坯体施加振幅与频率可控的振荡压力，克服了恒定压力烧结技术在颗粒重排、晶粒生长、气孔排出方面的缺陷，将传统的静态烧结发展为动态烧结。.研究了振荡压力烧结氧化锆陶瓷的致密化、晶粒生长及力学行为。振荡压力促进了氧化锆颗粒重排，在加速物质扩散、塑性流动的同时促进气孔排出，从而缩短了物质扩散路径，因此与低密度无压烧结氧化锆（PS，98.1%）相比，OPS氧化锆的体积密度达到99.7%。TEM、SEM分析表明OPS氧化锆陶瓷中发生显著的晶粒细化（283nm），而PS氧化锆、HP氧化锆的平均晶粒尺寸分别为460nm、307nm；同时，OPS氧化锆晶粒的长轴与短轴被控制在较窄的尺寸区间内。致密度的提高和晶粒尺寸的细化提高了OPS氧化锆的强度和韧性，PS、HP和OPS氮化硅的平均断裂强度分别为998MPa、1224MPa和1556MPa。.采用振荡压力烧结法制备了高强度、高韧性氮化硅陶瓷，研究了OPS 氮化硅溶解-析出过程中氮化硅相变、β-Si3N4晶粒生长及材料的强韧化机理。高温阶段施加振荡压力促进了液相中的颗粒的重排、物质迁移以及晶界处闭气孔排出，因而加速了材料的致密化，OPS氮化硅的密度达到3.36g/cm3。振荡压力提供了较高的扩散动力，OPS氮化硅沿直径方向上的生长速率明显加快，β-Si3N4晶粒的平均长径比降低。TEM研究表明氮化硅晶界处位错累积，同时β-Si3N4晶粒表面出现塑性条纹。HP氮化硅的弯曲强度和断裂韧性分别为936MPa、9.64MPa·m1/2；而振荡压力引起的致密度和晶粒尺寸的变化使OPS氮化硅的弯曲强度和断裂韧性分别达到1247MPa、10.04MPa·m1/2。.