Large-scale NiFe2O4-based Cermets Prepared by Composite Extrusion Modelling: from High-Qualified Composite Feedstock to Dense Sintered Microstructure

Combining with the advantages from mature technologies of fused deposition modelling and powder injection molding, 3D NiFe2O4-based cermet with weight over 1.3 kg and relative density of 95.8 % were fabricated by composite extrusion modelling using polyoxymethylene-based feedstock. Microstructure and rheological properties of the feedstock, roles of printing parameters on the morphology green samples and related catalytic debinding, sintering properties of cermets were investigated in detail. Uniformly dispersed cermet powders in feedstock were confirmed, due to the good wettability between the powders and binders. The feedstock with high solid loading of 58 vol.% exhibited shear-thinning behavior and contained high storage modulus for reliable shape retention. With optimized printing parameters, a high compression ratio (layer height/nozzle diameter) over 2.5 tended to shrink the size of stacking pores, resulting in dense green samples. Catalytic debinding was proved to be defect-free and efficient debinding route, which was successfully used to deal with dense cubic samples with thickness of 30mm. Sintered samples showed uniform microstructure with interconnected FeCuNi and Ni(Fe)Fe2O4 phases. Except for partial stacking pores in the fracture section, polished cermets exhibited mirror-like surfaces, indicating the good controlling of the final microstructure and performance of 3D cermets.