Al2O3p/钢分级构型复合材料的常压铸渗和强韧性调控

In the project, hierarchical structure is applied to fabricate Al2O3p/steel composites, accomplished with activation of superfine ceramic and metallic powders, to solve the problems of poor infiltration capability and bad comprehensive properties of strength and toughness of the composites. The method is described as below. First, Al2O3p in micrometer size are mixed uniformly with active powder, then pressed to form ball preforms in millimeter scale, furthermore, many balls form the final preform, finally, steel melt is poured and infiltrate into the preform to form the composites with hierarchical structure. The hierarchical structure of Al2O3p provides coarse way between the balls to facilitate melt infiltration, and also improve the comprehensive properties. The active ceramic powder on the surface of Al2O3p reacts chemically with the steel melt, so changes the infiltration mechanism, facilitates melt infiltration. The active metallic powder can adjust the chemical composition and mechanical properties of the matrix in the ball.areas. So, the cooperation effect between two matrices (matrix inside and outside of the ball area) provides a way to control the comprehensive properties of the composites.. The project researches the infiltration behavior of the melt and the comprehensive properties of strength and toughness of the composites, focuses on the effects of the hierarchical structure parameters, the activation effect of the powders on the infiltration depth and the comprehensive properties of the composites. Also, finite element simulation of computer, TEM, nanoindentation, 3D CT scanning technology will be applied to analyze the distribution of stress and strain in the microstructure, crack origination and propagation behavior, dislocation distribution. Finally, the infiltration mechanisms and strengthening, toughening mechanisms of the composites can be revealed, so the fabrication process can be optimized, and the comprehensive properties can be obviously improved..The project will provide support theoretically for the low cost fabrication and excellent comprehensive properties of Al2O3p/steel composites.

采用先进的分级构型复合思想，辅以陶瓷微粉和金属微粉活化技术，解决Al2O3颗粒增强钢基复合材料常压铸渗困难及其强韧性不足的问题。即将微米级Al2O3p与活性微粉混合，先制成毫米级预制球，再堆砌形成整体预制坯，最后进行常压铸渗，制备分级构型复合材料。利用预制球间的大通道以及活性微粉与钢液的化学反应，实现铸渗；利用构型结构、双基体协同作用调控MMCs的强韧性。项目研究构型结构参数、活性微粉与钢液的相互作用对钢-Al2O3体系反应性和润湿性的影响，揭示复合材料的常压铸渗机制；研究活性微粉对基体组织和强韧性的影响；结合计算机有限元模拟、三维显微CT、纳米压痕、TEM等技术，研究构型结构参数、双基体协同作用对复合材料强韧性的影响、裂纹的萌生和扩展行为、应力应变分布、位错分布等，掌握分级构型复合材料强韧化机制，提出强韧性调控方法，从而为Al2O3p/钢复合材料的制备成型一体化、强韧性提高奠定理论基础。

针对Al2O3颗粒增强钢基(Al2O3p/钢)复合材料常压铸渗困难及强韧性不足的问题，本项目采用先进的分级构型复合思想，研究Al2O3p/钢分级构型复合材料的常压重力铸渗制备和强韧性。. 首先，研究了Al2O3p/钢均匀分布复合材料的常压浸渗过程及机理。研究表明，水玻璃粘接Al2O3p预制体烧结时，Al2O3表面Al、O元素会扩散到水玻璃熔体中，形成NaO2-Al2O3-SiO2三元系玻璃相，在钢液浸渗时，玻璃相逃离预制体上浮去除，从而实现浸渗；烧结温度800℃最利于浸渗；B4C微粉会氧化进入玻璃相中，降低其熔点；SiC微粉能够与钢液发生反应。这些都促进了钢液浸渗。TiO2微粉和高锰钢中的Mn元素进入玻璃相，会形成高熔点Mn2TiO5和MnAl2O4等相，造成钢液浸渗困难和玻璃相残留过多。. 其次，采用两步混合法等三种工艺方法，解决了Al2O3p预制球在铸型中预置难的问题，成功实现了Al2O3p/钢分级构型复合材料的常压浸渗制备，并提出了其两阶段浸渗机理。. 进一步，研究了Al2O3p/钢均匀和分级构型复合材料的力学性能。结果表明，Al2O3p/钢构型复合材料的强塑性受II级基体的性能影响大，能够继承II级基体的强塑性特点。Cr12MoV钢基复合材料压缩强塑性都远高于高锰钢基。构型复合材料抗压强度随II级增强体（球形复合区）体积分数升高，先增后减，在 22.8 vol.%时最高，比基体和均匀复合材料分别提升26.4 %和489 %。I级基体强度提高也能一定程度提高复合材料力学性能。复合区内界面层残留太多玻璃相对复合材料强韧性都有害。复合区大小也有重要影响，Φ7复合区的Cr12MoV钢基分级构型复合材料压缩强度和断裂应变分别达到2166.8MPa和8.5%，而较小的复合区则内部界面玻璃相残留多，强塑性低。. 采用第一性原理和有限元模拟，证明了Al2O3p/钢界面纳米级非晶态Na2SiO3对界面结合有益，分析了构型参数对复合材料强塑性的影响，与实验相互印证。. 最后，提出了分级构型复合材料的强韧化机制，其中韧化机制主要是构型韧化机制和界面韧化机制，而强化机制主要是界面强化机制和应力状态强化机制。项目还提出了Al2O3p/钢分级构型复合材料的强塑性调控方法。