Papers by Keyword: High-Energy Ball Milling (HEM)

Abstract: The copper/paraffin nanocomposites were synthesized by high energy ball milling. Observation of the microstructure, comparison and ascertainment of the particle size of the composite were analyzed by transmission electron microscope. Then the composite was put into a home-made copper tube (5 mm in diameter, 20 mm in length, closed at one end) by thermoforming process, and its thermal sensitivity was measured using thermo-controlled optical micro measuring equipment. The effects of milling time on the microstructures and the thermal sensitivity of copper/paraffin nanocomposites were investigated. The results showed that different milling time caused the changes in particle size and shape of the composite, and had a significant effect on its thermal sensitivity. With increasing milling time, the thermal sensitivity of composite gradually increased.

Abstract: The structure and microwave properties of composites consisting of paraffin as a dielectric host matrix and Fe particles as inclusions have been studied. The composites were prepared by the mechanochemical synthesis and contain 7.7% vol. concentration of the inclusions. The microwave properties were studied in 0.1 to 6 GHz frequency range. The microwave properties of the composites are shown to depend mostly on the size and shape of the inclusions, with the phase composition of the inclusions exerting only a slight effect. With decreasing the inclusions size, the low-frequency peak (300−400 MHz) attributed to the domain wall motion diminishes.

Abstract: CNT-reinforced aluminum matrix composites was produced by high-energy ball milling, the effect of rotary speed and milling time on the particle size distribution,the density and hardness of CNT-aluminum matrix composites were studied,it was observed that the rotary speed and milling time have an important effect on the mechanical properties of the CNT-aluminum matrix composites.

Abstract: Cu-Zn alloy was prepared by high energy ball milling of elemental copper and zinc, With the Simoloyer attrition mill the particle around 10µm with good particle-size distributions can be made in 100 min. Through the analysis by TG-DTA, XRD, SEM, the results show that Cu-Zn alloys can be produced by ball milling without the formation of oxide even milling in the air atmosphere and subsequent heat treatment at 350°C, it indicated that the formation of the oxide can be avoided during ball milling by adding Al.

Abstract: In this work, the effect of the milling time on the densification of the alumina ceramics with or without 5wt.%Y2O3, is evaluated, using high-energy ball milling. The milling was performed with different times of 0, 2, 5 or 10 hours. All powders, milled at different times, were characterized by X-Ray Diffraction presenting a reduction of the crystalline degree and crystallite size as function of the milling time increasing. The powders were compacted by cold uniaxial pressing and sintered at 1550°C-60min. Green density of the compacts presented an increasing as function of the milling time and sintered samples presented evolution on the densification as function of the reduction of the crystallite size of the milled powders.

Abstract: The effect of mechanical activation procedures on the combustion synthesis of NbAl3 was investigated. The activation was carried out by a two-step high energy ball milling procedure. In the first milling, aluminum and niobium were milled separately (pre-activation). The mixture of pre-activated powders was then activated in the second milling. Reaction synthesis, by simultaneous combustion mode, was conducted on compacted pellets made of powder mixtures with and without pre-activation. The thermal behavior of the compacted pellets upon heating was recorded and the main thermal combustion reaction characteristics were evaluated. The two-step procedure produced aggregates with a globular dispersion of niobium due to increased particle hardness and decreasing mean particle size during pre-activation milling. Analysis of pellet thermal behavior showed the two-step milling procedure could enhance reaction performance by increasing maximum reaction heating rate and temperature gain during reaction.

Abstract: This work reports the efforts to obtain TiFe intermetallic compound by high-energy ball milling of Ti and Fe powder mixtures. This process route has been used to provide a better hydrogen intake in this compound. Milling was carried out in a SPEX mill at different times. Strong adherence of material at the vial walls was seen to be the main problem at milling times higher than 1 hour. Attempts to solve this problem were accomplished by adding different process control agents, like ethanol, stearic acid, low density polyethylene, benzene and cyclohexane at variable quantities and keeping constant other milling parameters like ball to powder ration and balls size. Better results were attained with benzene and cyclohexane, but with partial formation of TiFe compound even after a heat treatment (annealing) of the milled samples.

Abstract: The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.

Abstract: High frequency induction heated sintering (HFIHS) method is one of the rapid sintering methods. The advantage of rapid sintering method is that grain growth can be prevented during sintering at high temperature. Refinement of grains was known to increase the yield and flow stresses of crystals. The relation between the yield stress and the grain size is known as Hall-Petch relation. NbC-10vol.%Co, Ni and Fe composites were fabricated by HFIHS at 1060°C for 0 and 3 min as holding times under a pressure of 80MPa.The relative density of NbC-10vol.%Co, Ni and Fe composites which were sintered at 1060°C for 0min as holding time under 80MPa were 91.90%, 91.26% and 91.26%, respectively. These composites are difficult to use industrial parts due to low relative density. The longer sintering time was conducted for increasing relative density in this study. Nano-sized specimens, which were calculated grain size by full-width at half maximum (FWHM), can be obtained by HFIHS. The value of hardness and fracture toughness was investigated using 20kgf load Vickers indenter.

Abstract: SiC nanoparticles (40nm) reinforced metal matrix composites (MMCs) were made by a common stir casting technique in two different preparation processing routes. In the first route, the coated ceramic powder was prepared using electroless plating to coat SiC nanoparticles by Cu. In the second route, Cu and SiC nanoparticles were fully mixed by high energy ball milling, and then SiC nanoparticles were embedded in Cu to form a “jujube-cake” structure. In both cases the average particles size were 0.2μm. The SiC nanoparticles enhanced A6061 alloy matrix composites were made by stir casting, and as-cast microstructures were studied by means of optical microscopy (OM) and scanning electron microscopy (SEM). The results show that in the first route, the Cu off and the slagging reaction occurs to form a mixture at the upper part of the ingot by a vacuum melting and the ingot central also has a large number of pores, only the lower part of the ingot organization is uniform. The second route can make better uniform composites.