致密超细晶氧化铝纳米晶陶瓷的制备与断裂韧性研究

Alumina ceramic is the most widely used ceramic. But its brittleness limits its wider applications. Nanocrystalline microstructure can give alumina nanocrystalline ceramic good toughness through plastic deformation mechanisms such as grain boundary/triple junction diffusion, grain gliding, and grain rotation. As disperse fine α alumina nanoparticles smaller than 15 nm are unusually difficult to prepare, efforts to produce dense alumina nanocrystalline ceramic with grains smaller than 50 nm had not succeeded. The applicant has broken through the bottleneck problem of preparing disperse fine (<10 nm) α alumina nanoparticles and successfully sintered dense (99.7%) fine-grained (36 nm) alumina nanocrystalline ceramic. Based on our these results, the present project will optimize the improved two-step sintering process and pressurelessly sinter dense (>99.5%) fine-grained (≤33 nm) alumina nanocrystalline ceramic. Ultrahigh pressure hot pressing sintering will be applied to sinter dense (>99.5%) ultrafine-grained (≤15 nm) alumina nanocrystalline ceramic. The variation in fracture toughness and hardness of alumina nanocrystalline ceramic with grain size will be studied. The toughening and hardening mechanisms in alumina nanocrystalline ceramic will be revealed. Finally, alumina nanocrystalline ceramic with high fracture toughnesses (≥15MPa√m) will be developed. Alumina nanocrystalline ceramic of high fracture toughnesses has a vast application prospect in civil and defense fields.

氧化铝陶瓷是应用最广的陶瓷，但脆性限制了其更广泛应用。纳米晶微结构可通过晶界和三叉晶界扩散、晶粒滑动、晶粒转动等机制发生塑性变形，赋予氧化铝纳米晶陶瓷良好韧性。由于分散细小(<15nm)α氧化铝纳米颗粒的制备异常困难，致密细晶(<50nm)氧化铝纳米晶陶瓷的制备是不成功的。申请者在突破分散细小(<10nm) α氧化铝纳米颗粒制备瓶颈难题和成功烧结致密(99.7%)细晶(36nm)的氧化铝纳米晶陶瓷的基础上，本项目拟优化改进的两步烧结法工艺，无压烧结致密(>99.5%)细晶(≤33nm)氧化铝纳米晶陶瓷。超高压热压烧结制备致密(>99.5%)超细晶(≤15nm)氧化铝纳米晶陶瓷。研究氧化铝纳米晶陶瓷断裂韧性和硬度随晶粒尺寸的变化规律，揭示超细晶氧化铝纳米晶陶瓷的韧化和强化机理，开发高断裂韧性(≥15MPa√m)氧化铝纳米晶陶瓷。高断裂韧性氧化铝纳米晶陶瓷在国防、民用领域具有广阔的应用前景。

陶瓷的脆性限制了其更广泛应用。本项目研究高断裂韧性氧化铝纳米晶陶瓷。无压两步烧结制备相对密度>99.5%、晶粒尺寸33 nm的致密细晶Al2O3纳米晶陶瓷。高压和超高压热压烧结制备相对密度>99.5%、晶粒尺寸≤15 nm的致密超细晶Al2O3纳米晶陶瓷。分析陶瓷纯度、晶体结构、平均晶粒尺寸及其分布。分析晶界和三叉晶界体积分数随晶粒尺寸的变化。分析致密Al2O3纳米晶陶瓷的强化机制。分析Al2O3纳米晶陶瓷断裂韧性随晶粒尺寸的变化规律，分析韧化机制。.制备了完全分散、高纯、最细小（平均尺寸3.3 nm）、尺寸分布窄、比表面积最高（253 m2/g）、等轴的α-Al2O3纳米颗粒。发现超细α-Al2O3纳米颗粒在室温长时间存放发生明显颗粒长大。超细α-Al2O3纳米颗粒低温退火时展示极低的长大激活能（0.25 eV），坯体烧结时展示较低的晶界扩散激活能。超细α-Al2O3纳米颗粒在室温展示以0.01 s-1的应变速率发生90%形变的赝弹性行为。无压两步烧结制备了无压烧结条件下晶粒最细（30 nm）、晶粒尺寸超均匀、致密Al2O3纳米晶陶瓷。高压两步热压烧结、真空处理制备了至今晶粒最细（9.2 nm）、近乎致密（98.8%）的Al2O3纳米晶陶瓷。Al2O3纳米晶陶瓷硬度随平均晶粒尺寸d变化，在d>84 nm时，符合正常Hall-Petch关系。暗示硬化机理为细晶强化。细晶致密Al2O3纳米晶陶瓷的断裂韧性高达4.8 MPam，是常规多晶氧化铝陶瓷断裂韧性的最高值。对Al2O3纳米晶陶瓷显微压痕应变区域的微结构分析表明，韧化机理为借助晶界滑动和晶粒旋转的塑性变形。.本项目部分成果被Science报道。本项目的完成推进了Al2O3纳米晶陶瓷的研究，为开发韧性Al2O3陶瓷迈步出了关键一步。