Analysis of the rheological behavior of Fe trimodal micro-nano powder feedstock in micro powder injection molding

Debinding of Yttria-Stabilised Zirconia/Bimodal Stainless Steel 316L Bi-Materials Produced through Two-Component Micro-Powder Injection Moulding

The fabrication of bi-material micro-components via two-component micro-powder injection moulding (2C-µPIM) from 3 mol% yttria-stabilised zirconia (3YSZ) and micro/nano bimodal stainless steel 316L (SS 316L) powders has received insufficient attention. Apart from this, retaining the bonding between ceramic and metal at different processing stages of 2C-µPIM is challenging. This study investigated the solvent and thermal debinding mechanisms of green bi-material micro-parts of 3YSZ and bimodal SS 316L without collapsing the ceramic/metal joining. In this research, feedstocks were prepared by integrating the powders individually with palm stearin and low-density polyethylene binders. The results demonstrated that during the solvent debinding process, the palm stearin removal rate in the bi-materials composed of 3YSZ and bimodally configured SS 316L feedstocks intensified with an increase in temperature. The establishment of interconnected pores in the solvent-debound components facilitated the thermal debinding process, which removed 99% of the binder system. Following sintering, the debound bi-materials exhibited a relative density of 95.3%. According to a study of the microstructures using field emission scanning electron microscopy, an adequate bond between 3YSZ and bimodal SS 316L was established in the micro-part after sintering. The bi-material sintered at 1350 °C had the highest hardness of 1017.4 HV along the joining region.

Micro-Injection Molding and Debinding Behavior of Hydroxyapatite/Zirconia Bi-Materials Fabricated by Two-Component Micro-Powder Injection Molding Process

The micro-scale joining of two different materials using two-component micro-powder injection molding (2C-µPIM) is an intriguing technique. The formation of defects in bi-materials at different processing stages makes this technique challenging. This study presents the fabrication of defect-free bi-material micro-parts containing hydroxyapatite (HA) and 3 mol% yttria-stabilized zirconia (3YSZ) via 2C-µPIM. Critical powder volume concentrations (CPVCs) of 61.7 vol% and 47.1 vol% were obtained for the HA and 3YSZ powders, respectively. Based on the CPVCs, the optimal loadings for the HA and 3YSZ powders were selected as 60 vol% and 45 vol%, respectively. The HA and 3YSZ feedstocks were prepared by separately mixing the optimal powder contents with low-density polyethylene (LDPE) and palm stearin binders. The feedstocks displayed pseudoplastic behavior, and the lowest ranges of viscosity for the HA and 3YSZ at a temperature of 180 °C were 157.1-1392.5 Pa·s and 726.2-985.5 Pa·s, respectively. The feedstocks were injected to produce green HA/3YSZ micro-sized components. It was found that a solvent debinding temperature of 70 °C removed 60.6% of the palm stearin binder from the sample. In the thermal debinding stage, the open channels that formed in the bi-material sample's solvent debound at 70 °C and contributed to the removal of 93 to 95% of the binder system. When the debound bi-materials were sintered at 1300 °C, the highest relative density of 96.3% was obtained. The sintering operation revealed a linear shrinkage between 13 and 17% in the sintered HA/3YSZ micro-parts.

Study of solid loading of feedstock using trimodal iron powders for extrusion based additive manufacturing

Volume loading of feedstock using trimodal iron (Fe) powders was investigated for the application of extrusion-based additive manufacturing (AM). Fe trimodal powder composed of nano, sub-nano, and micro particles was manufactured via the powder metallurgy process where small particles behave as rolling bearings among large particles, and thereby improving the flow characteristics of feedstock by minimizing friction among the particles. The flow behavior and microstructures of the monomodal feedstock were compared with those of the trimodal feedstock. We have confirmed that the critical powder loading of monomodal powder was measured to be 70 vol.% while trimodal powder showed up to 74 vol.%. Furthermore, trimodal feedstocks of 60, 65, 70, 75, and 80 vol.% Fe powder were prepared to determine the optimal powder content for sintering. As a result, the feedstock with powder content of 70 vol.% gave the highest sintered density of 92.32%, the highest Vickers hardness of 80.67 HV, with the smallest dimensional variation in shrinkage, proposing 70 vol.% of trimodal feedstock to be the suitable powder content for AM. Finally, its microstructural and mechanical comparison with 70 vol.% sintered part using monomodal Fe powder, showed that the sintered part using trimodal feedstock displayed higher hardness, uniform shrinkage as well as smaller grain size, confirming trimodal feedstock to be favorable for the application of extrusion-based AM.

Synthesis of Ti–Al Bimodal Powder for High Flowability Feedstock by Electrical Explosion of Wires

In this research, Ti–Al bimodal powders were produced by simultaneous electrical explosion of titanium and aluminum wires. The resulting powders were used to prepare powder–polymer feedstocks. Material characterization involving X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and melt flow index (MFI) determination were carried out to characterize bimodal powders obtained and evaluate the influence of the powder composition on the feedstock flowability. The bimodal distribution of particles in powders has been found to be achieved at a current density of 1.2 × 107 A/cm2 (the rate of energy input is 56.5 J/μs). An increase in the current density to 1.6 × 107 A/cm2 leads to a decrease in the content of micron particles and turning into a monomodal particle size distribution. The use of bimodal powders for powder–polymer feedstocks allows to achieve higher MFI values compared with monomodal powders. In addition, the use of electroexplosive synthesis of bimodal powders makes it possible to achieve a homogeneous distribution of micro- and nanoparticles in the feedstock.

Sintering Behavior of Bi-Material Micro-Component of 17-4PH Stainless Steel and Yttria-Stabilized Zirconia Produced by Two-Component Micro-Powder Injection Molding Process

In this research, we investigated the influence of the sintering temperature on the physical and mechanical properties of micro-sized bi-material components of 17-4PH stainless steel and 3 mol% yttria-stabilized zirconia fabricated using a two-component micro-powder injection molding (2C-μPIM) process. First, 17-4PH and zirconia powders were separately mixed with binders to obtain feedstocks, which were then injection-molded into the dumbbell shape, followed by the binder extraction process. Subsequently, the debound micro-specimens were subjected to sintering between 1250 °C and 1350 °C for 3 h. Per the observations of the microstructures using scanning electron microscopy (SEM), a strong bond between metal and ceramic in micro-sized 17-4PH/zirconia components was formed when the sintering temperature exceeded 1300 °C. The maximum relative density of 99% was achieved when the bi-material micro-part was sintered at 1350 °C. The linear shrinkage increased from 9.6% to 17.4% when the sintering temperature was increased from 1250 °C to 1350 °C. The highest hardness value of 1439.6 HV was achieved at 1350 °C along the bi-material bonding region. Moreover, a maximum tensile strength of 13.7 MPa was obtained at 1350 °C.

Rheology of Highly Concentrated Suspensions with a Bimodal Size Distribution of Solid Particles for Powder Injection Molding

Powder injection molding (PIM) is one of the modern and prospective technologies in processing different materials. We proposed to use bimodal compositions of particles for increasing their content in the final products. A set of model suspension of Al with low-molecular-weight poly (ethylene glycol) as a binder based on theoretical arguments concerning the filling capacity of bimodal suspensions was prepared. Studying the rheological properties of these compositions showed that they demonstrate elasto-viscous behavior with significant plasticity that is favorable for the technological process. Using compositions with bimodal distributions allows for increasing the content of the solid phase up to 75 vol. % for PIM technology, which is significantly higher than the standard practical limit. This rheological approach developed for model formulations was applied to processing compositions containing aluminum oxide as typical ceramics and polyolefines as a binder widely used in technological practice. The obtained sintered ceramic samples have quite acceptable mechanical properties of the usual corundum articles.