Effect of Short Attritor-Milling of Magnesium Alloy Powder Prior to Spark Plasma Sintering

The spark plasma sintering (SPS) technique was employed to prepare compacts from (i) gas-atomized and (ii) attritor-milled AE42 magnesium powder. Short attritor-milling was used mainly to disrupt the MgO shell covering the powder particles and, in turn, to enhance consolidation during sintering. Compacts prepared by SPS from the milled powder featured finer microstructures than compacts consolidated from gas-atomized powder (i.e., without milling), regardless of the sintering temperatures in the range of 400–550 °C. Furthermore, the grain growth associated with the increase in the sintering temperature in these samples was less pronounced than in the samples prepared from gas-atomized particles. Consequently, the mechanical properties were significantly enhanced in the material made of milled powder. Apart from grain refinement, the improvements in mechanical performance were attributed to the synergic effect of the irregular shape of the milled particles and better consolidation due to effectively disrupted MgO shells, thus suppressing the crack formation and propagation during loading. These results suggest that relatively short milling of magnesium alloy powder can be effectively used to achieve superior mechanical properties during consolidation by SPS even at relatively low temperatures.

Microstructure and Mechanical Strength of Attritor-Milled and Spark Plasma Sintered Mg-4Y-3Nd Alloy

Gas-atomized powder of an Mg-4Y-3Nd magnesium alloy was attritor-milled at room temperature in an argon atmosphere for two time periods—1.5 and 5 h. Subsequently, the gas-atomized powder as well as both of the milled powders were spark plasma sintered at four temperatures, 400, 450, 500, and 550 °C, for 3 min. The effect of the milling on the powder particles’ morphology and the microstructure of the consolidated samples were studied by advanced microscopy techniques. The effect of the microstructural changes, resulting from the pre-milling and the sintering temperature, on the mechanical strength was investigated in compression along and perpendicular to the sintering load direction. Both the compression yield strength and ultimate compression strength were significantly affected by the grain size refinement, residual strain, secondary phase particles, and porosity. The results showed that attritor-milling imposed severe deformation to the powder particles, causing a significant grain size refinement in all of the consolidated samples. However, 1.5 h of milling was insufficient to achieve uniform refinement, and these samples also exhibited a distinctive anisotropy in the mechanical properties. Only a negligible anisotropy and superior yield strength were observed in the samples sintered from 5 h milled powder, whereas the ultimate strength was lower than that of the samples sintered from the gas-atomized powder.

Microstructure Formation and Performance of Reactive Sintered Titanium Oxycarbide Base Ceramic-Ceramic Composites

Reactive sintering is a process where synthesis reaction of the ceramic phases is combined with sintering (densification) of the composite. Dense lightweight titanium oxycarbide-aluminium oxide ceramic-ceramic composites were produced from titanium dioxide, carbon black as graphite source and aluminium precursors by high energy attritor milling, followed by reactive sintering. Titanium oxycarbide and aluminium oxide phases were synthesized during reactive sintering in situ. To investigate the microstructure evolution and phase formation, the specimens were sintered at different temperatures (600-1725 °C) in vacuum. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure and phase formation. Mechanical performance (hardness and fracture toughness) was evaluated.

Anaerobic vs. aerobic preparation of silicon nanoparticles by stirred media milling. The effects of dioxygen, milling solvent, and milling time on particle size, surface area, crystallinity, surface/near-surface composition, and reactivity

Silicon nanoparticles milled anaerobically in heptane or mesitylene are smaller and much more reactive than SiNPs milled aerobically in the same solvents for equal attritor milling times.

Characterization of 14YWT As-Atomized, Milled, Milled and Annealed Powders and HIP Consolidated Alloys

ABSTRACTNanostructured ferritic alloys (NFA) are Fe-Cr based ferritic stainless steels containing an ultrahigh density of very stable Y-Ti-O nanofeatures (NFs) that provide dispersion strengthening and radiation damage resistance for candidate Generation IV and future fusion reactor materials. This work is a small and focused part of a larger collaboration to produce large best practice NFA heats. The powders analyzed were rapidly solidified from a melt containing Fe-14%Cr, 3%W, 0.4%Ti and 0.2%Y by gas atomization in Ar, Ar/O, and He atmospheres. Note this represents a different processing path from conventional NFA production where metallic powders are mechanically alloyed with Y2O3 by ball milling. Electron probe microanalysis (EPMA), atom probe tomography (APT), transmission electron microscopy (TEM) and small angle neutron scattering (SANS) were used to characterize the powders in the as-atomized, ball milled and ball milled and annealed conditions. EPMA showed the Y is heterogeneously distributed and phase separated in all the as atomized powders, but attritor milling for 20 to 40 h is required to mix the Y. Milling also creates a significant quantity of O as well as N contamination. Subsequent powder annealing treatments, typically at 1150°C, result in the precipitation of a high density of NFs. All the annealed powder variants show a bimodal grain size distribution, but TEM and APT show NFs in both large and small grains. Reducing O content added during milling of the Ar atomized powders increased the precipitate size and decreased the number density, adversely affecting the hardness.

A Novel Way of Dispersing Fine Ceramic Particles in PLGA Matrix

α-tricalcium phosphate (α-TCP) was prepared by a wet precipitation reaction between calcium hydroxide and orthophosphoric acid solutions. The as-synthesised powder was then characterised using a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscope (EDS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscope (FTIR). Analyses revealed that a phase-pure powder with a Ca/P ratio of 1.5 was produced. In addition, nanosized α-TCP particles of diameter ~ 70 nm were agglomerated to form larger particles of 10μm in diameter. It was found that by the combination of attritor milling and solution evaporation, the agglomerates of α-TCP nanoparticles could be broken down, and distributed evenly within the poly(D,L-lactic-co-glycolic acid) (PLGA) matrix. Thus, a α-TCP/PLGA nanocomposite was successfully produced by a modified solution evaporation method at room temperature followed by hot pressing at 150 °C. The achievable ceramic loading was approximately 38 wt.%, which was confirmed by thermal gravimetric analysis (TGA).