超高温Al2O3/GAP/ZrO2共晶陶瓷激光立体成形及其非规则生长与转变机制

Directionally solidified oxide eutectic in-situ composite ceramics present excellent high-temperature strength, superior oxidation and creep resistance, as well as outstanding microstructural stability at elevated temperatures, which have been considered to be the most promising ones for new generations of ultra-high-temperature structural materials serviced at high-temperature oxidizing atmosphere over a long period of time. However, the development and application of the materials are greatly restricted due to the low solidification rate, redundant procedure of preparing sintered precursor, high cost and difficulty of preparing large and complexly shaped specimens for the present eutectic ceramic preparation methods. Laser solid forming (LDF) is an advanced additive fabrication technique, which can rapidly prepare metal parts with different shapes and size, and specially with high density up to 100%. In the present proposal, rapid one-step fabrication of the novel Al2O3/GAP/ZrO2 ternary ultra-high- temperature eutectic in-situ composite ceramic with free of cracks and sintering procedure, and with ultra-fine microstructure is developed by combining the oxide composite ceramic design and LDF technique. The ternary Al2O3/GAP/ZrO2 eutectic ceramics is prepared directly from the oxide powders using modified LDF method by high temperature preheating, and accurately controlling and optimizing the forming process. The mutual operation rule of the laser beam, oxide powders and matrix is investigated. The intrinsic irregular eutectic growth and transformation mechanism, and the strengthening and toughening mechanism of the ternary composite ceramic are systematically revealed. On the basis, the relationship of LDF parameter- microstructure control-material performance is estabised. The fundamental investigation of this project is to provide theoretical foundation and technical support for developing new ultra-high-temperature oxide eutectic ceramics with large size, high density, high strength and toughness, and to further enrich and develop eutectic solidification theory.

氧化物共晶陶瓷以其优异的高温力学性能被认为是新一代超高温氧化性气氛中长期工作的新型先进结构材料。目前定向凝固方法制备共晶陶瓷存在凝固速率低、需制备烧结预制体、成本高及难以获得大尺寸和形状复杂试件等问题。激光立体成形是一种先进的增材制造技术，能不受尺寸和形状限制快速高效制备致密度近乎100%的高性能金属零件。本项目拟将激光立体成形快速凝固技术与氧化物复相陶瓷成分设计相结合，以氧化物共晶粉末为原料，采用激光立体成形技术，通过高温预热、精确控制和优化激光立体成形凝固过程，一步制备无需预烧结、无裂纹、组织超细化的高强高韧性Al2O3/GAP/ZrO2超高温共晶复相陶瓷，探明激光束、陶瓷粉末及基材的相互作用，揭示三元高熔化熵小平面相非规则共晶生长与转变机制及共晶陶瓷强韧化机理，建立激光成形参数-组织控制-性能的相互关系，为开发大尺寸、高致密、高强高韧性超高温氧化物陶瓷及其制备技术提供理论和技术支撑。

氧化物共晶陶瓷以其优异的高温力学性能被认为是新一代超高温氧化性气氛中长期工作的新型先进结构材料。本项目突破共晶陶瓷传统方法熔化难、成形尺寸和形状限制等瓶颈，利用激光立体成形技术一步制备了无需预烧结、组织细化的高强韧Al2O3/GAP/ZrO2超高温共晶复相陶瓷，揭示了三元高熔化熵小平面相非规则共晶生长与转变机制及共晶陶瓷强韧化机理，建立激光成形参数-组织控制-性能之间的相互关系，为开发大尺寸、高致密、高强高韧性超高温氧化物陶瓷及其制备技术提供了理论和技术支撑。主要研究结果如下：..1)获得了氧化物共晶陶瓷激光立体成形送给粉末的选择，粉末的均匀混合和改性方法，建立了陶瓷粉末造粒和预烧制工艺，探明了送给粉末的形貌特征和微观结构。.2)建立了具有自主知识产权适于氧化物共晶陶瓷激光立体成形的表面气氛加热系统。设备最高加热温度1400oC，有效抑制了共晶陶瓷在激光立体成形冷却过程中裂纹和孔洞的产生。.3)探明了激光功率、扫描速率、送粉率以及层厚等工艺参数对共晶复合陶瓷成形质量的影响规律。在优化的成形工艺参数下，获得了表面光滑、内部致密的Al2O3/GAP二元和Al2O3/GAP/ZrO2三元共晶陶瓷。.4)激光立体成形Al2O3/GAP/ZrO2共晶复合陶瓷由无规则连续分布的 a-Al2O3，GAP及c-ZrO2三相组成，形成原位镶嵌的三维连续网状结构，属典型的非规则共晶组织。随凝固速率的增加，共晶组织由象形文字结构转变为象形文字与胞状组织共存的结构，且出现明显的规则化趋势。.5)揭示了非规则共晶的生长机制。Al2O3/GAP/ZrO2共晶呈现典型的小平面/非小平面非规则共晶生长，Al2O3相以小平面方式生长，GAP和ZrO2相以非小平面生长。在高的生长速率下，共晶存在小平面向非小平面生长方式的转变。.6)Al2O3/GAP/ZrO2共晶陶瓷平均室温断裂韧性为7.06 MPa.m1/2。Al2O3/GAP共晶陶瓷弯曲强度达到1.14GPa。1500oC热暴露250小时，组织未发生明显变化，表现出优异的组织稳定性和抗氧化性能。..本项目相关研究结果发表学术论文20篇，其中SCI收录19篇，包括本领域TOP1期刊J Eur Ceram Soc 3篇和Scripta Mater 3篇。获授权发明专利14项。参加国际学术会议4次，其中特邀报告1次。