Investigation and two-stage modeling of sintering behavior of nano/micro-bimodal powders

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.

Mathematical modeling of high-energy materials rheological behavior in 3D printing technology

In this paper, a mathematical model of the extrusion process in 3D printing of high-energy composites is studied. These composites are formed from polymer binder and powder with bimodal particles obtained by electric explosion technique. The main difficulty of extrusion 3D printing method is primarily linked to the high viscosity of utilized material, especially one with high concentration of particles. In this case, the viscosity of the initial mixture depends on the pressure, temperature and concentration of the filler, as well as on the particle dispersion. Under certain conditions the ignition of high-energy material in the nozzle is possible, thus the search for optimal printing parameters based on the mathematical modeling and the following experimental verification are the main purposes of the current work.

Carbon-coated iron nanopowder as a sintering aid for water-atomized iron powder

The paper examines the influence of carbon coating on iron nanopowder used as a sintering aid for water-atomized iron powder. Iron nanopowder without such a coating was used as a reference sintering aid to isolate the influence of the carbon coating. Both nanopowder variants were characterised using XPS and HRTEM. The results showed a core–shell structure for both variants. The iron nanopowder is covered by a 3–4 nm thick iron oxide layer, while the carbon-coated iron nanopowder is encapsulated with several nanometric carbon layers. Thermogravimetry conducted in a pure hydrogen environment shows a multipeak behaviour for the carbon-coated iron nanopowder, while a single peak behaviour is observed for the iron nanopowder. Two types of micro/nanobimodal powders were obtained by mixing the nanopowder with water-atomized iron powder. Improved linear shrinkage was observed during sintering when the carbon-coated iron nanopowder was added. This can be explained by the reduction in surface diffusion in the nanopowder caused by the carbon coating, which allows the nanopowder to sinter at higher temperatures and improves densification. Carbon and oxygen analysis, density measurements, optical microscopy and JMatPro calculations were also performed.

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.

Preparation of Nano/Micro Bimodal Aluminum Powder by Electrical Explosion of Wires

Electrical explosion of aluminum wires has been shown to be a versatile method for the preparation of bimodal nano/micro powders. The energy input into the wire has been found to determine the relative content of fine and coarse particles in bimodal aluminum powders. The use of aluminum bimodal powders has been shown to be promising for the development of high flowability feedstocks for metal injection molding and material extrusion additive manufacturing.