Powder-binder separation in injection moulded green parts

For powder injection moulding (PIM) the ceramic powder is mixed with a thermoplastic binder system to achieve an injectable feedstock. In contrast to injection moulding of polymeric components, the binder must be removed after the shaping step before sintering the ceramic part to full density. During the mould filling process shear forces act on the blend that might cause separations of powder particles and binder. In this case polymer films form at the mould surface and at internal interfaces which induce microstructural defects in the debinded part. In particular for multi-component parts this effect is critical since binder films in the joining zone weaken the bonding strength between the two components that might even lead to delamination. For detecting binder separations within the injection moulded bulk material and at joining zones of two-component parts the microstructure of green samples has been studied. Since conventional machining techniques like grinding and polishing modify the original structure, e.g. when particles are pulled out of the matrix and binder smears onto the surface, a special ceramographic method for the preparation of cross-sections was applied. This approach bases on broad ion beam techniques and enables the simultaneous polishing of hard ceramic particles and soft polymer molecules without destroying the structure or producing a relief at the surface. In the analysed samples binder accumulations were found along flow lines, at weld lines, at boundaries of so-called dead water regions and at the interface of two-component parts.