Development of the powder injection moulding process and evaluation of the property profile of short-fiber reinforced oxide-oxide-composites

氧化物-氧化物陶瓷基复合材料是一种具有广泛应用前景的高温材料。虽然连续纤维增强氧化物陶瓷已经达到了先进的水平，但短纤维增强材料仍处于非常早期的发展阶段。特别是通过粉末注射成型(PIM)生产的材料很少被研究。由于粉末注射成形是一种非常经济实惠的工艺，因此将在建议的项目中评估通过注射成型生产的短纤维增强氧化物材料的潜力。该项目的目标是开发一条工艺链，用于通过粉末注射成型生产具有更高断裂韧性和可观强度的短纤维增强陶瓷零件。这包括通过控制微观结构参数的变化来评估可获得的机械性能。研究集中在弱基体复合材料(WMC)上，其中多孔基体和弱纤维-基体界面控制着裂纹的扩展机制。首先，必须开发合适的原料，使纤维在螺杆挤出机中混合时保持可接受的长度。由于纤维在成型过程中对齐，因此了解纤维取向与成型过程中流动条件之间的关系是非常重要的。为此目的，测量的纤维取向将与计算的剪切速率曲线相关联。此外，还必须开发一种工艺来实现短纤维增强CMC的无缺陷脱脂。为了使增强短纤维有效，必须控制随后的烧结过程中基质的固结。必须量身定制基体组织和纤维-基体界面强度，避免纤维损伤。为了实现这一目标，将研究无压烧结和压力辅助烧结技术。合适的工艺参数将通过烧结体的微观结构和力学特性来确定。纤维推入试验将被用来评估纤维的脱粘和拔出效果。在最佳条件下固化的材料将用于随后的机械性能的基本评估。这些研究的目的是将最重要的微观结构参数，如纤维含量和纤维取向与定向力学性能相关联，并了解各自的微结构-性能关系。为了获得高温行为的第一印象，将对一些选定的材料进行弯曲蠕变实验。

Oxide-oxide ceramic matrix composites are attractive materials for miscellaneous high temperature applications. While an advanced state is reached for continuous fiber reinforced oxide ceramics, short fiber reinforced materials are still in a very early stage of development. Particularly materials produced by powder injection molding (PIM) are rarely investigated. As PIM is a very cost-effective process, the potential of short fiber reinforced oxide-oxide materials produced by injection molding will be evaluated within the proposed project.Objective target of the project is the development of a process chain for the production of short fiber reinforced ceramic parts with enhanced fracture toughness and appreciable strength by powder injection molding. This covers an assessment of the attainable mechanical properties by variation of the controlling microstructural parameters. The investigations concentrate on weak matrix composites (WMC), where a porous matrix and thereby a weak fiber-matrix interface control the mechanisms of crack propagation.Initially, suitable feedstocks have to be developed, where the fibers keep an acceptable length during compounding in a screw extruder. As the fibers align during molding, it is essential to understand the correlation between fiber orientation and flow conditions during the molding step. Measured fiber orientations will be correlated with calculated shear rate profiles for this purpose. Additionally, a process has to be developed for a defect free debinding of the short fiber reinforced CMCs.Making the reinforcing short fibers effective, consolidation of the matrix in the subsequent sintering process has to be controlled. The matrix microstructure and the fiber-matrix interface strength have to be tailored and fiber damage must be avoided. Pressureless and pressure assisted sintering techniques will be investigated to reach this goal. Suitable process parameters will be identified by microstructural and mechanical characterization of sintered compacts. Fiber push-in tests will be used to evaluate debonding and pull-out effects of the fibers.Materials consolidated under optimum conditions will be used for a subsequent fundamental assessment of mechanical properties. Aim of these studies is to correlate the most important microstructural parameters, e.g. fiber content and fiber orientation with the directional mechanical properties and to understand the respective microstructure-property relations. To receive a first impression on high temperature behavior, bending creep experiments will be carried out for a number of selected materials.