Debinding and presintering of high aspect ratio microbi-lumen tubes produced by extrusion of 17-4PH feedstock

Recent developments have showcased that micro-extrusion of feedstock can be used for manufacturing metallic microbi-lumen tubes with very high length-to-diameter aspect ratios, which are not viable by conventional metal extrusion or commonly used feedstock processing technologies like injection molding or hot pressing. The extrusion of high aspect ratio microcomponents faces the challenge of maintaining the geometrical accuracy, surface finish, and structural properties since the micro-extrusion in green state is followed by debinding and sintering operations, which result in shrinkage and variations in surface finish and structure. The stages of the process chain such as solvent/thermal debinding (TD), to remove the polymeric binder, and presintering (PS), to achieve a mild structural rigidity before the sintering, are of critical importance to achieve the surface and structural properties of high aspect ratio microparts and have not been yet studied in case of micro-extrusion of feedstock. In this study, the effect of debinding and PS on surface and structural properties of bi-lumen tubes processed at different extrusion conditions is discussed. Surface roughness of the tubes is analyzed using three-dimensional microscopy, and structural properties are studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The debinding and PS experiments on extruded microbi-lumen tubes retained very good surfaces integrity without any cracks or defects. The study shows that the interactions of extrusion temperature and extrusion velocity influence the surface finish of the extruded tubes the most. The sintered bi-lumen samples showed a good areal surface finish, Sa of 2.21 μm, which is near to the green state value confirming the suitability of the applied debinding and PS parameters.