Critical Solid Loading Research Articles

Microstructural and core loss behaviors of addictive Fe-17 at% P based on Fe-3.5 wt% Si alloys in powder injection molding

This study investigated Fe-17 at% P addition effects on the magnetic properties of Fe-3.5 wt% Si alloys to enhance the electrical resistivity and core loss in powder injection molding. Considering the lowest melting point for 17 at% of P in the Fe-P phase diagram, the effect of P in Fe-3.5 wt% Si was analyzed by adding Fe-17 at% P from 0 to 12 wt% with 4 wt% increments. The feedstocks were prepared based on the processing optimization with respect to the critical solid loading, mixing homogeneity, and binder decomposition. The microstructure; relative density; electrical resistivity; and C, O, N, and S impurities of the sintered alloys were analyzed in correlation with the magnetic properties. The magnetic induction (B5000), maximum permeability, coercivity at 400 Hz and core loss in the frequency range from 50 to 1000 Hz at 1 T were analyzed. The higher magnetic induction and the lower eddy current loss with increasing Fe-17 at% P addition were induced by the higher relative density and electrical resistivity, respectively.

Direct calculation of inter-particle distance in suspension by image processing

With the difficulties to measure inter-particle distance in a suspension, the theoretical value under the several assumptions has been used. In this study, an image processing method for directly calculating inter-particle distances in a suspension was developed. This method enables inter-particle distances to be calculated regardless of the particle size, distribution, and morphology. A surface of suspension composed of particles and wax-polymeric binder was polished with acetone to expose the particles from the binder. The particles measured by scanning electron microscope were distinguished from the binder through the developed image processing method based on the intensity difference between the particles and binder. The inter-particle distances between the randomly selected particles and neighboring particles were calculated using the centroids and boundaries obtained by image processing. To determine the inter-particle distance as a representative value, a Monte Carlo method was employed. The inter-particle variation was defined to determine the iteration number for the Monte Carlo method. Finally, the inter-particle distances for the particle volume fraction of 40 and 50 vol% were obtained by the developed method. In addition, this developed method is available to describe the physical phenomenon such as a powder-binder separation and critical solid loading.

Effect of binder composition on rheological behavior of PMN-PZT ceramic feedstock

An investigation of the effect of binder composition on rheological behavior of lead magnesium niobate–lead zirconate titanate (PMN-PZT) ceramic feedstock is presented in this paper. Rheological behavior is the key factor for manufacturing a micro-sized structure with high aspect-ratio. Each binder composition was categorized into three groups to analyze the effect based on the variation of ratio within filler (first), within backbone (second), and between filler and backbone (third). The critical solids loading for each feedstock was evaluated using a torque rheometer. To compare the net effect of binder composition, all the feedstocks were mixed with the solids loading of 45 vol%. The effects of binder composition on rheology were analyzed using a capillary rheometer with different shear rates and temperatures. The main rheological parameters, such as viscosity, shear sensitivity, and temperature sensitivity, were closely related to the molecular weight difference in binder composition. First, the viscosity increased as the ratio of binders with higher molecular weight increased for each group. Second, the sensitivity of viscosity on shear rate was enhanced with the increase of polyethylene (PE) in the second and backbone in the third, respectively. Third, the sensitivity of viscosity on temperature was lowered as the amount of binders with higher molecular weight increased for each group. Based on the experimental results, the moldability index as a function of viscosity, shear sensitivity, and temperature sensitivity was calculated. The feedstock with the largest amount of filler showed the best rheological property for powder injection molding.

Thermal decomposition behavior of nano/micro bimodal feedstock with different solids loading

Debinding is one of the most critical processes for powder injection molding. The parts in debinding process are vulnerable to defect formation, and long processing time of debinding decreases production rate of whole process. In order to determine the optimal condition for debinding process, decomposition behavior of feedstock should be understood. Since nano powder affects the decomposition behavior of feedstock, nano powder effect needs to be investigated for nano/micro bimodal feedstock. In this research, nano powder effect on decomposition behavior of nano/micro bimodal feedstock has been studied. Bimodal powders were fabricated with different ratios of nano powder, and the critical solids loading of each powder was measured by torque rheometer. Three different feedstocks were fabricated for each powder depending on solids loading condition. Thermogravimetric analysis (TGA) experiment was carried out to analyze the thermal decomposition behavior of the feedstocks, and decomposition activation energy was calculated. The result indicated nano powder showed limited effect on feedstocks in lower solids loading condition than optimal range. Whereas, it highly influenced the decomposition behavior in optimal solids loading condition by causing polymer chain scission with high viscosity.

Two Component Injection Moulding of Bi-material of Stainless Steel and Yttria Stabilized Zirconia – Green Part

The two component injection molding (2C-PIM) is a promising technique for production of small, complex and high density, metal-ceramic parts in large scales. This method is a viable option for integrating incompatible functions or properties of the materials in a singular part or component. Thus, the production of near net shaped components via 2C-PIM is imperative due to cost effectiveness resulting from high unit volumes. In this study, the feasibility of joining stainless steel (17-4PH) and 3mol% yttria stabilized zirconia (3YSZ) materials in their green states was investigated. Two feedstock of SS17-4PH and 3YSZ powder materials was prepared based on optimum solid loading of 3vol% lower than value of the critical loading. The critical solid loading for the SS17-4PH and 3YSZ powder materials were 71vol% and 53vol% respectively, based on the oil absorption technique ASTM: D-281-12. The binder system utilized comprises of 60wt.% palm stearin (PS) and 40wt.% low density polyethylene (LDPE). The two materials were injected sequentially using the screw type injection molding machine (BOY 22A) to form a bi-material component. The green properties were investigated. The morphology of the individual green parts and composites depicted that the powders were optimally dispersed in the binder matrix indicating good mixture and compaction of the green components. The flexural strength of the single components of the bi-material was above 5 MPa. The strength of the bonding zone which was 1.4 MPa indicates an evidence of bonding.

Development of powder injection molding process for sintered soft magnet with the addition of Fe-17 at.% P powder

Soft magnetic powder injection molding is a net-shape production technology to fabricate sintered soft magnets. Powder injection molding technology for soft magnetic materials can be expected to develop a new type of electromagnetic components with the miniaturization and complexity design. In this work, 8 wt.% of iron-phosphorus powders (Fe-17 at.% P) were added to carbonyl iron powders to improve the magnetic performances with PIM process. Soft magnetic feedstocks were fabricated by optimized PIM process using a wax-based binder system. The critical solids loading of feedstocks were measured to determine the optimal solids loading, and injection molding process was conducted for the PIMed soft magnetic parts. The effect of Fe-17 at.% P addition to carbonyl iron powder was investigated on the sintering behaviors and magnetic properties. It was observed that sample with Fe-17 at.% P addition had optimum relative density (99.8%) and magnetic polarization (28,299 Gauss) at sintering temperature 1400°C in a hydrogen atmosphere.

Rheological and thermal debinding properties of blended elemental Ti-6Al-4V powder injection molding feedstock

The rheological and thermal debinding properties of a feedstock play an important role in the molding and debinding stage of powder injection molding (PIM), and can directly determine the quality of final PIM product. This work focuses on the rheological and thermal debinding properties of blended elemental Ti-6Al-4V (BE Ti64) PIM feedstock with a comparison study of pure titanium (Ti) feedstock. The effects of 60Al-40V alloy addition, on the attributes of BE Ti64 feedstock; including critical solids loading, rheological behavior, and binder decomposition behavior, were studied using torque rheometry, capillary rheometry, and thermogravimetric analysis. The critical solids loading of BE Ti64 (66vol.%) was somewhat lower value than the Ti feedstock (69vol.%), due to the different in particle characteristics. Both BE Ti64 and Ti feedstocks exhibited non-Newtonian shear-thinning behavior. The difference in flow activation energies for the two feedstocks indicates that the BE Ti64 feedstock is more sensitive to temperature compared to the Ti feedstock. During thermal debinding, both the feedstocks exhibited a dual-sigmoid, binder-decomposition behavior with only minor differences in activation energy.

Influence of nano powder on rheological behavior of bimodal feedstock in powder injection molding

Rheological behavior of feedstock, which highly affects the condition of green body, is substantial issue in powder injection molding process. In this paper, the influence of nano powder contents in bimodal feedstock on solids loading and rheological behavior has been investigated. The bimodal powders were fabricated with 100nm and 4μm sized 316L stainless steel powders, and mixed with wax-based binder system. The critical solids loading for each powder was measured by torque rheometer. In order to analyze net effect of nano powder ratio, all feedstocks were formulated as solids loading of 42vol.%. Feedstock homogeneity was evaluated by rotational rheometer. Capillary rheometer test was conducted to measure the viscosity of feedstock with different temperatures, shear rates and nano powder ratios. Rheological parameters, like flow index, flow activation energy and moldability index, were calculated based on the capillary rheometer test. The results indicated the critical solids loading and feedstock homogeneity decreased as nano power ratio increased in bimodal feedstock. Rheological parameters were also affected by nano powder ratio, and the optimal mixing ratio of nano powder for moldability index was investigated as 12vol.%.

Effect of nanopowder ratio in bimodal powder mixture on powder injection molding

One of the significant advantages of nanopowder is activated sintering and better surface finish of the final components. However, because of its drawbacks like higher cost and low formability, the mixture of nano and micro powder emerged as an effective solution. In this research, effects of nanopowder in nano/micro bimodal feedstock were studied. Bimodal powder in feedstock was prepared with nano and micro sized powders. These powders were mixed with different nanopowder volume ratio from 0 to 50%. The effects of nanopowder vol.% on the critical solids loading was investigated with rheometer experiments. From debinding behavior, apparent debinding activation energy for each feedstock was determined. Sintering behavior of micro and bimodal feedstocks were analyzed by dilatometer and compared with die compacted specimen. Nanopowder effect on sintered density and hardness of the samples were verified as well.

Experimental investigation on blockage boundary for pneumatic conveying of powders in narrow bifurcation slits

ABSTRACTTo investigate the blockage characteristics for dense-phase pneumatic conveying in narrow bifurcation slits, a study on the blockage boundary conditions of powders was undertaken. The results show that the solid mass flow rate for blockage increases with superficial air velocity, and the variation trend can be divided into three typical stages. Besides the relationship between the solid loading ratio and superficial air velocity for blockage in the bifurcation slit displays a “S” shape with the increase of air velocity, the solid loading ratio increases, then decreases, finally increases, and in each stage above, the relationship between the two approximately meets power function, respectively. According to the “S” shape relationship, the formula used for blockage boundary [Setia, Mallick, Wypych, and Pan (2013). Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems, Particuology, 11, 657–663] was modified into piecewise function for bifurcation slits. In addition, with the increase of the bifurcation angle and conveying pressure, the superficial air velocity decreases, while the solid mass flow rate and the critical solid loading ratio increase. The research work could help understand the blockage theory of the dense-phase pneumatic conveying.

Preparation of Ti-6Al-4V feedstock for titanium powder injection molding

Titanium powder injection molding (Ti-PIM), combining the advantages of both powder metallurgy and plastic injection molding, is an effective manufacturing technology for a near net shape production of titanium parts. In this work, titanium feedstock was fabricated by mixing the pre-alloyed Ti-6Al-4V powder with a wax-polymer binder system after determining their critical solid loading percentage. The rheological and binder decomposition behaviors of prepared feedstock were investigated. The results showed that the feedstock had a critical solid loading of 71 vol. % and the flow activation energy for fabricated feedstock was 64 kJ/mol. The binders were decomposed with two sigmoids functions, where the activation energies for the first and second sigmoid decomposition were 68 kJ/mol and 224 kJ/mol, respectively. The results indicated that the Ti-6Al-4V feedstock was well prepared and would provide good rheological and thermal decomposition behaviors for injection molding and thermal debinding process in Ti-PIM.

Fabrication, bioactivity, in vitro cytotoxicity and cell viability of cryo-treated nanohydroxyapatite–gelatin–polyvinyl alcohol macroporous scaffold

Freeze casting and cryogenic treatment both low temperature process have been employed to fabricate nanobiocomposite hydroxyapatite (HA)–gelatin–polyvinyl alcohol (PVA) macroporous scaffolds from synthesized three different spherical, rod and fibrous HA nanoparticles and composition optimized vis-á-vis porosity architecture, content and compressive strength. A critical HA morphology, solid loading and liquid nitrogen interaction time have a significant effect to enhance the mechanical response of developed scaffolds. Cryo-treated 40 wt.% nanorod HA–gelatin–PVA scaffold posses interconnected pore structure with 80 vol.% porosity, average pore diameter 50–200 μm and highest 5.8 MPa compressive strength. Different degree of the apatite deposition phenomenon in simulated body fluid solution at 37 °C and pH ∼ 7.4 varies with respect to time. In vitro cytotoxicity and L929 mouse fibroblast cell culture in the presence of Dulbecco's Modified Eagle Medium and 10% Fetal Bovine Serum at 37 °C and 5% CO2 atmosphere exhibit excellent cytocompatibility and cell viability at low extract concentration up to 25%.

Investigation on blockage boundary condition of dense-phase pneumatic conveying in bending slits

The estimation on the blockage boundary condition is significantly important for dense-phase pneumatic conveying of particles through bending slits. This paper presented the blockage characteristics for dense-phase pneumatic conveying in a bending slit. The bending slits with different bending angles were established, and the blockage boundary conditions were investigated in detail. The results show that the critical solid loading ratio for blockage initially decreases with the increase of superficial air velocity with different conveying pressures and bending angles of the slits, which agree with the existing studies and the current theories. Furthermore, it was found that there exist a minimum solid loading ratio, and when superficial air velocity is greater than that of the minimum solid loading ratio, the solid loading ratio actually begins to increase with the increase of air velocity. Meanwhile, with the increasing of the bending angle and the conveying pressure, the critical solid loading ratio increases, and the minimum solid loading ratio for blockage also increases. Therefore, the efficient and economical blockage of slits could be obtained by adopting the minimum solid loading ratio and its corresponding superficial air velocity.

Effect of Dry and Wet Ball Milling Process on Critical Powder Loading and Mixture Properties of Fine WC-10Co-0.8VC Powder

Micro powder injection molding (μPIM) has great potential for the production of micro cemented carbide parts that require high hardness and toughness. The main stages of the μPIM process include mixing the powder and organic binder, injecting, debinding, and sintering. High critical solid loading of submicron tungsten carbide (WC) powder is one of the requirements in the micro powder injection molding process, which is not obtained easily. This paper investigates the effects of ball milling on critical solid loading of submicron WC. Dry and wet ball milling processes were used to prepare a powder mixture with composition of WC-10Co-0.8VC (wt-%). Critical powder volume concentration (CPVC) was determined using the torque variation method, and the powder characteristics were assessed using scanning electron microscopy and energy dispersive X-ray spectroscopy. CPVC was at 42% and 50% for the dry and wet ball milling processes, respectively. Apparent and tap densities of the powder mixture were achieved at 2.4 g/cm3 and 2.96 g/cm3 after dry milling and at 2.54 g/cm3 and 3.39 g/cm3 after wet milling, respectively. Wet ball milling causes fine particles to de-agglomerate and improves the critical solid loading, which is advantageous for submicron cemented tungsten carbide injection molding. The homogeneity of the powder mixture can improve under longer time of wet milling process and it can be expected that reduce microstructure defects in sintered components.

Critical Solid Loading and Rheological Study of WC-10%Co

Micro powder injection molding (µPIM) is a preferred technology for the production of micro parts or micro structured parts which derived from the well known thermoplastic injection molding technique. It is suitable for a large-scale production of ceramic and metallic parts without final machining. In the hardmetal industry, submicron and ultrafine hardmetals are the most demanding and also the fastest growing grades in production and application. Four stages involve in µPIM are mixing, injection, debinding and sintering. The volumetric ratio of solid powder to the total volume of powder and binder, which is usually called powder loading, largely determines the success or failure of subsequent processes. Critical solid loading of the powder can be estimated by torque variation, density, melt flow, density and viscosity versus composition. In this paper, critical solid loading of WC-10%Co is determined using torque variation method and its rheological behavior is studied. During the process, the wet surface of the powder particle WC-10%Co will cohesive together and resulted to the torque. Progressive powder is added-in after torque decrease and critical solid loading is identified when torque becomes unstable. Hence, critical solid loading WC-10%Co with WC (APS < 1 µm) is 46% and 42, 43 and 44 vol% of powder loading are selected to mix with wax-based binder system. The viscosity of feedstock show the pseudoplastic behavior and flow index (n) are 0.444, 0.491 and 0.492 for powder loading 42%, 43% and 44% respectively.

Preparation of high nitrogen and nickel-free austenitic stainless steel by powder injection molding

High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of “nickel-allergy” and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding (PIM) technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64 vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintering conditions are determined to be 1300°C, 2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150°C for 90 min and water quench, the 0.2% yield strength, ultimate tensile strength (UTS), elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.

Homogeneity of Aqueous Al<sub>2</sub>O<sub>3</sub>/3Y-TZP Feedstock by Plastic Kneading

The effects of different kneading sequences, chemical additives, and solid loadings to the homogeneity and rheological behavior of the Al2O3/3Y-TZP (ZTA) feedstock were investigated. The properties of the feedstock were analyzed by the torque rheometry, transmission optical microscopy (OM) and scanning and transmission electron microscopy (SEM & TEM). The optimal kneading process was determined when good homogeneity was reached. The concepts of critical solid loading and the homogeneity of two-oxide systems, and the power consumption to reach best microstructure will be introduced and quantitatively analyzed.

The Influences of Solid Loading and Molding Variables on Alumina Injection Molding

Two kinds of commercial alumina compacts made by injection molding with different solid loading are studied. Solid loading is the key factor for the injection molding process and the properties of green body and sintered compacts. The results show that higher solid loading leads to better properties of the compacts such as density and fracture strength, however the viscosity of the feedstock would increase. Smaller sized alumina powder leads to a higher critical solid loading value. Macroscopic defects such as voids and cracks could be introduced into the injection molding samples if the molding variables are not optimized. The properties of sample are improved by adjusting the variables such as injection pressure, holding pressure, holding time and barrel temperature.

Drying-induced forming of alumina ceramics using high solid-loaded slurries with addition of glycerol

A new drying-induced forming (DIF) of ceramics has been developed using high solid-loaded alumina slurries with addition of glycerol, in which the slurry was simply dried in an open mold at the ambient condition. The drying-induced forming approach is facilitated by the high stability of concentrated slurries during drying where glycerol was added to maximize the critical solid loading and play simultaneously as a drying control agent. The drying and rheological behaviors of slurries were examined with respect to the glycerol addition. A slurry of 60 vol% solid loading with 20 wt% glycerol addition was chosen for the drying induced forming test. The green samples exhibited no bending or cracks, and a small degree of shrinkage anisotropy during sintering. The sintered samples showed a high relative density of 99.2% and an average strength of 420 MPa. We demonstrate here a possibility of producing near-net-shaped and bulk ceramic components in a simple scheme by using the drying-induced approach.

Effects of surfactant on properties of MIM feedstock

Effects of the surfactant for improving the properties of MIM feedstock were investigated. Feedstocks were prepared by 17-4PH stainless steel(SS) powder and paraffin wax-based binder containing different contents of stearic acid(SA) as the surfactant. The viscosity of the feedstock decreases significantly when the SA is added. Besides, the wetting angle of the binder against the 17-4PH SS powder decreases greatly and the critical solid loading increases with the adding of the SA. Fourier transformation infrared spectroscopy(FTIR) analysis was used to prove the interaction between the SA and the 17-4PH SS powder. Chemical bonding is found on the surface of 17-4PH SS powder after mixing and it helps a lot to enhance the interacting force between the binder and the powder. Then an adsorbing model was adopted to estimate the least content of the surfactant that formed a monolayer adsorption on the mono-sized spherical powder (with smooth surface). The least content of the surfactant is calculated to be 0.19%. Whereas, the experiments indicate that about 5% is the optimal value to improve the properties of the feedstock. The reason may come from two aspects: firstly, the powders used in current experiment are not all mono-sized spheres and the coarse surface of the powder has a great effect on the adsorptive capacity of the powder; secondly, multilayer adsorption is likely to occur on the powder surface, which will also increase the adsorptive capacity.