陶瓷微喷射粘结自由成形的高致密化及层界面连接增强机理研究

Binder-jetting freeforming (also referred to as Three-Dimensional Printing, 3DP) directly uses ceramic powder as raw material, exhibiting the benefits of low running cost, fine environmental friendliness and fast process speed, so it is an ideal additive manufacturing method for refractory structural ceramics. However, due to the poor flowability of fine powder, this forming method can hardly attain dense structures for the formed ceramic green parts. Moreover, the printed areas are humid and thus have a sticky effect on the flow of powder material, which results in the loose-packing powder structures within interlayer regions of the formed green parts and accordingly makes the bond between the adjacent layers not sufficient after sintering. Based on the aim to form green ceramic parts with high relative densities and reinforce the bond between layer structures of the sintered ceramic parts, this project covers the following researches: the packing theory of multi-modal powder system and the mechanism of “dip-coating” of solid-phase adhesive onto the ceramic matrix powder are both investigated, by which the powder material is reformed to strengthen its own dense-packing ability; additionally, the collaborative influences of powder-layering process and humidity on the flow of powder material are investigated, and thus, the forming-process parameters are improved to promote the densification effect during powder layering; furthermore, the parametric control method for electrohydrodynamic (EHD) spraying is studied, and thereby, a novel inter-layer reinforcing (ILR) mechanism, which can be described as “EHD spraying and depositing the preceramic microparticles onto the interlayer regions within ceramic green parts to improve the in-situ sintering activities”, is systematically explored. The research results will offer both theoretical and technical basis to the high-quality forming of varieties of refractory structural ceramic parts, and moreover, have great significance that it will satisfy the demand of forming refractory ceramic structures for the aeronautics and astronautics applications.

微喷射粘结自由成形技术可对陶瓷粉末直接成形，其运行成本低、环境友好、成形速度快，是高温结构陶瓷增材制造的理想工艺。该技术的缺陷为：小粒径粉末流动性差，很难成形高致密陶瓷坯体；湿润的喷印区域对粉末流动具有粘滞作用，成形坯体的层间界面区域会因此形成松散的粉体结构，烧结后难以实现可靠的界面连接。本项目以成形高致密陶瓷坯体和增强烧结坯体层界面连接为目标，研究多粒径粉末系统的空间填充理论以及固相粘结剂“浸渍覆膜”陶瓷基体粉末的工艺控制机理，优化成形粉末组成，提高其密排性能；研究铺粉操作和环境湿度对粉末流动的协同作用机制，优化成形工艺参数，提升铺粉致密化效果；研究静电雾化工艺的参数化控制方法，探索在坯体层界面上雾化沉积陶瓷先驱体微颗粒来提高界面区域烧结性能的层间增强机理。本项目研究成果可为各类高温结构陶瓷的高质量成形提供理论依据和技术参考，对满足航空航天领域耐高温陶瓷结构的制备需求具有重要现实意义。

增材制造可以赋予陶瓷制备更好的工艺灵活性，基于喷墨打印原理的喷射粘结（3DP或称BJP）增材制造工艺适用于制备较大尺度坯体、成形速度快且具有较好的成形精度，但是该方法分层铺粉过程中粉末流动性差且仅适用于几十微米粒径尺度的陶瓷粉末进行坯体成形，因此制备的陶瓷坯体相对密度低、最终烧结难以获得较好的结构与力学性能。本项目面向成形材料制备、3DP成形工艺、辅助成形工艺以及后处理强化流程开展系统化研究。基于空间填充优化的粉末粒径分析和脲醛树脂（UF）缩聚固化机理制备了高性能、配制流程快捷的成形粉末和喷射液，可以在使用较少粘结剂的前提下实现较好粘结强度，从而粘结剂的减少“造孔效应”；进一步对铺粉过程进行了理论建模与行为分析，通过有效的铺粉方法和铺粉参数的设计实现了3DP成形坯体组织结构的调控和高致密坯体制备；同时深入研究了静电雾化陶瓷先驱体微滴辅助3DP成形的坯体强化工艺，面向不同雾化效应对静电雾化参数实现了有效调控，但通过强化机理分析发现雾化渗入的先驱体结构不能在高温煅烧后给予陶瓷坯体烧显著的结强化效应；此外，本项目还补充研究了亚微米陶瓷浆料浸渍渗透强化工艺，对不同组织结构的陶瓷坯体探明了浆料渗透和强化机理，并进一步通过后处理优化控制，实现了渗透性能提升，最终实现了相对密度近90%、抗弯和抗压强度分别为91.9MPa和813.2MPa的陶瓷制件；并且对该项目流程应用于工程实际进行了预研究和未来展望。本项目面向通用陶瓷材料体系，包含材料制备、装备开发、成形工艺参数优化以及后处理流程控制等工艺因素，完整提供了一套可以使用易获得易操作的设备器具、在常压条件下可便捷化实施的高性能陶瓷制件3DP制备工艺流程，显著改善了3DP陶瓷制备领域坯体致密度低、最终制件力学性能不佳的问题。