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

• Applicants: Dr.-Ing. Rainer Oberacker; Dr.-Ing. Volker Piotter
• Subject Area: Glass, Ceramics and Derived Composites ; Materials in Sintering Processes and Generative Manufacturing Processes
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269896286

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.

• DFG Programme: Research Grants