Synthesis of Nano-Size AlN Powders by Carbothermal Reduction from Plasma-Assisted Ball Milling Precursor

Nano-size aluminum nitride （A1N） powders have been successfully synthesized with a high efficiency method through annealing from milling assisted by discharge plasma （p-milling） alumina （Al2O3） precursors. The characterization of the p-milling Al2O3 powders and the synthesized AlN are investigated. Compared to conventional ball milling （c-milling）, it can be found that the precursors by p-milling have a finer grain size with a higher specific surface area, which lead to a faster reaction efficiency and higher conversion to A1N at lower temperatures. The activation energy of p-milling Al2O3 is found to be 371.5 kJ/mol, a value that is much less than the reported value of the unmilled and the conventional milled Al2O3. Meanwhile, the synthesized AlN powders have unique features, such as an irregular lamp-like morphology with uniform particle distribution and fine average particle size. The results are attributed to the unique synergistic effect of p-milling, which is the effect of deformation, fracture, and cold welding of Al2O3 powders resulting from ball milling, that will be enhanced due to the introduction of discharge plasma.

Enhancement of the Hydrogen Storage Properties of Mg/C Nanocomposites Prepared by Reactive Milling with Molybdenum

The effect of Mo on the morphology, crystal structure and hydrogen sorption properties of Mg/C composites prepared by reactive milling was studied. Transmission electron microscopic（TEM） observation shows that Mg/C composites prepared with the addition of Mo are of nanoscale with particle size about 20-120 nm after 3 h of milling under 1 MPaH2. MgH2 of tetrahedral crystal structure predominates in the materials with the geometric shape of oblique hexagonal prism. From X-ray diffraction（XRD） and hydrogen content studies, Mo and crystallitic carbon have a synergistic effect on promoting the hydrogenation rate in the reactive milling process. From differential scanning calorimetric（DSC） studies, the dehydrogenation peak temperature of the Mg/C materials with Mo is lowered to 299-340 ℃.

Surface quality investigation in high-speed dry milling of Ti-6Al-4V by using 2D ultrasonic-vibration-assisted milling platform

Ultrasonic-vibration-assisted milling(UVAM)is an advanced method for the efficient and precise machining of difficult-to-machine materials in modern manufacturing.However,the milling efficiency is limited because the ultrasonic vibration toolholder ER16 collet has a critical cutting speed.Thus,a 2D UVAM platform is built to ensure precision machining efficiency and improve the surface quality without changing the milling toolholder.To evaluate this 2D UVAM platform,ultrasonic-vibration-assisted high-speed dry milling(UVAHSDM)is performed to process a titanium alloy(Ti-6Al-4V)on the platform,and the milling temperature,surface roughness,and residual stresses are selected as the important indicators for performance analysis.The results show that the intermittent cutting mechanism of UVAHSDM combined with the specific spindle speed,feed speed,and vibration amplitude can reduce the milling temperature and improve the texture of the machined surface.Compared with conventional milling,UVAHSDM reduces surface roughness and peak-groove surface profile values and extends the range of residual surface compressive stresses from−413.96 MPa to−600.18 MPa.The excellent processing performance demonstrates the feasibility and validity of applying this 2D UVAM platform for investigating surface quality achieved under UVAHSDM.