جستجوی مقالات مرتبط با کلیدواژه "mechanical alloying" در نشریات گروه "شیمی"

The mechanical alloying (MA) procedure was used to synthesize the Ni50Al50 and Ni50Al45Mo5 nanocrystalline intermetallic compound using the pure Ni, Al and Mo elemental powders under an argon atmosphere for different times (8, 16, 48, 80 and 128 h) in a planetary ball mill with hardened steel balls (12 balls-1cm and 4 balls-2cm in diameter). The mechanical alloying was carried out in the attendance of various Mo contents as a micro-alloying element for various milling times. Microstructural characterization and structural changes of powder particles during mechanical alloying were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Outcomes confirmed that the synthesis behavior of NiAl intermetallic depends on the milling time and Mo content. The results show that after than 80h milling, the intermetallic phase is produced after opening the vial lid. X-ray map show that, in the fixed milling time, enhancing the Mo content leads to acceleration in the NiAl formation in air atmosphere. The mechanical alloyed powders have a microstructure consisting of nanometer size particles. Mo enhance has a considerable effect on the lowering of crystallite size. The TEM image showed that the Ni50Al45Mo5 nano-particles were less than 10 nm. The average grain size is smaller than those sizes obtained in the NiAl (25 – 35 nm) alloy.

In this study, Cu50-Ni50 alloy were synthesized by mechanical alloying. The alloy was then reinforced by dispersion of multiwalled carbon nanotubes using a planetary high energy ball mill. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer were used to evaluate the effects of CNT addition on the characteristics of the nanocomposites. XRD results of Cu-Ni sample showed that, the homogeneous Cu50-Ni50 alloy with a mean crystallite size of 25 nm was formed after 10 h of milling. It was found that presence of CNTs and the stage of CNT addition can alter the phase composition, morphology and magnetic properties of the nanocomposites. Also, CNTs prevent the complete dissolution of nickel in copper and change the chemical composition of the alloy. SEM micrographs revealed that the addition of CNTs caused a significant reduction of powder particle size. More ever, the distribution of CNTs in the matrix decreases the saturation magnetization and increases the coercivity of the nanocomposites.

In this research, mechanical alloying was used to produce Ti-50Al, Ti-45Al-5Cr and Ti-45Al-5W (at%) alloys. The effect of ternary addition (Cr and W) on microstructure and production efficiency of TiAl alloy were investigated. Alloying was performed in a planetary mill and the milling time varying from 5 to 70h. The structural evaluation in these powders was done by X-ray diffraction (XRD) technique and Scanning Electron Microscopy (SEM) during mechanical alloying and after annealing at 1100°C in vacuum oven. The results showed only a complete amorphous phase after 50h of milling of Ti-50Al powder mixture, but with 5at% addition of Cr, the Cr (Ti, Al) solid solution within the amorphous matrix were identified after 70h milling and with 5at% addition of W, the W lattice was remained with amorphous phase. The time required for solid solution or amorphous phase formation was longer in Cr and W containing powders. After annealing of mechanically alloyed Ti-50Al, the γ-phase with high purity and nanostructured size was produced and for sample with Cr addition, the TiAl(γ) with amount of Ti3Al(a2) were formed and for sample with W addition, the duplex phase (γ+a2) with a minor amount of W, were formed.

Solid solutions of Ag-Cu were prepared via ball milling process, for about 5-30 h. The Cu-20at%Ag and Cu-3.64at%Ag composition were investigated by X-ray diffraction technique. It was realized that the solid solubility level could be increased by increasing the initial solute content in the mixture. In addition, shifts in peak positions of silver and copper were observed with milling time. The dissolution volume was estimated by thermodynamic relations and was compared with the measured values using X-ray diffraction technique and it was observed that the measured and calculated volumes agreed well. The final dissolution volume of 39.155 litters was calculated by thermodynamic relationship.

In this research, the high-energy planetary mill was employed to produce nanocrystalline Ti-50Al(γ)(at%) powders. Initial powders were mechanically alloyed in 99.9999% and 90% purities of Argon and also Air atmosphere with alloying times up to 50h. The effect of impurity of Argon atmosphere on the microstructure and the rate of phase transformation of Ti-50Al were investigated during mechanical alloying and after annealing at 1000°c. The results showed that the formation of nanostructure TiAl(γ) phase had directly related to the impurities of atmosphere in vials. The impurity of the atmosphere could delay the rate of amoprphization during mechanical alloying and decrease the rate of mechanical alloying process beside some unwanted phases which were produced in powder mixture. The powder particles produced in the high purity Argon atmosphere seemed to be finer than those in the atmosphere. The X-ray patterns, SEM analysis, changes in grain size and DTA test were studied during mechanical alloying and after annealing.