Metal injection molding is a growing technology for producing complex metallic components. Preparation of feedstock for metal injection molding is a very crucial step during this process. This is because the deficiencies in quality of the feedstock once made, cannot be corrected by subsequent processing steps. One of the challenges in producing the feedstock is its formulation. In this study, the effect of the percentage of carnauba wax along with other binder constituents of paraffin wax, polypropylene and stearic acid is investigated on the density, strength, hardness and rheological behavior of a part, made of 4605 low alloy steel powder using metal injection molding process. For this reason, six binder systems including paraffin wax, polypropylene and stearic acid having different percentages of carnauba wax have been produced. After preparation of the samples, tensile testing, Vickers hardness test, density and rheological behavior of the samples have been measured and compared. The results show that carnauba wax as a part of feedstock, has a positive effect on the strength and density while negative effect on the hardness of the final sintered part. Also with the increase in the percentage of the carnauba wax inside the polymer binder, the viscosity of the feedstock was reduced significantly.
The good interaction between the ceramic powder and the binder system is vital for ceramic injection molding and prevents the phase separation during processing. Due to the non-polar structure of polyolefins such as high-density polyethylene (HDPE) and the polar surface of ceramics such as zirconia, there is not appropriate adhesion between them. In this study, the effect of adding high-density polyethylene grafted with acrylic acid (AAHDPE), with high polarity and strong adhesion to the powder, on the rheological, thermal and chemical properties of polymer composites highly filled with zirconia and feedstocks was evaluated. To gain a deeper understanding of the effect of each component, formulations containing different amounts of HDPE and or AAHDPE, zirconia and paraffin wax (PW) were prepared. Attenuated total reflection spectroscopy (ATR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rotational and capillary rheology were used for the characterization of the different formulations. The ATR analysis revealed the formation of hydrogen bonds between the hydroxyl groups on the zirconia surface and AAHDPE. The improved powder-binder adhesion in the formulations with more AAHDPE resulted in a better powder dispersion and homogeneous mixtures, as observed by SEM. DSC results revealed that the addition of AAHDPE, PW and zirconia effect the melting and crystallization temperature and crystallinity of the binder, the polymer-filled system and feedstocks. The better powder--binder adhesion and powder dispersion effectively decreased the viscosity of the highly filled polymer composites and feedstocks with AAHDPE; this showed the potential of grafted polymers as binders for ceramic injection molding.
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