Papers by Keyword: Mechanical Alloying (MA)

Abstract: The object of our research is to combine the properties of Mangalloys and nanoscale advantages in order to enhance the performance and extend the range of applications in the field of work-hardening parts such as railroad components, armor, and modern auto components. We have produced a high-manganese austenitic steel nanomaterial containing more than 12 wt% Mn, which is the level of Mn in Hadfield steel. This study experimentally determined the process of phase transitions involved in Fe–13 wt% Mn–1.2 wt% C alloy during mechano-synthesis and after subsequent annealing. The milling time ranged from 0.5 to 24 h. The unique features of the nanocrystalline structure and the changes in microstructure as a function of milling time were investigated by X-ray diffraction analysis, differential scanning calorimetry, and scanning electron microscopy coupled with EDX. The grain sizes and microstrain of the milled powder were determined. A thorough study has been done on the sample where a new phase fcc (at 24h of MA) was formed.The object of our research is to combine the properties of Mangalloys and nanoscale advantages in order to enhance the performance and extend the range of applications in the field of work-hardening parts such as railroad components, armor, and modern auto components. We have produced a high-manganese austenitic steel nanomaterial containing more than 12 wt% Mn, which is the level of Mn in Hadfield steel. This study experimentally determined the process of phase transitions involved in Fe–13 wt% Mn–1.2 wt% C alloy during mechano-synthesis and after subsequent annealing. The milling time ranged from 0.5 to 24 h. The unique features of the nanocrystalline structure and the changes in microstructure as a function of milling time were investigated by X-ray diffraction analysis, differential scanning calorimetry, and scanning electron microscopy coupled with EDX. The grain sizes and microstrain of the milled powder were determined. A thorough study has been done on the sample where a new phase fcc (at 24h of MA) was formed.

Abstract: The new type of copper matrix self-lubricating composites were prepared by powder metallurgy route. The influences of milling way and content of molybdenum disulfide on composites’ microstructure and tribological properties were researched. It is found that, M_oS₂ can’t participate in the process of mechanical alloying together with graphite and copper powder. When the mass fraction of M_oS₂ increases from 0% to 10%, the coefficient of friction of composites M_oS₂-G-C_u reduces correspondingly, however the three-dimensional network structure of copper matrix was damaged seriously in sample 10% M_oS₂-G-C_u .After the wear text there will come out solid self-lubricating film on the surface of sample 5% M_oS₂-G-C_u and 10% M_oS₂-G-C_u .

Abstract: Nanostructured Powders of Ni-20wt%Al and Ni-50wt%Al Were Prepared, by Mechanical Alloying under an Argon Atmosphere, from Elemental Ni and Al Powders Using a Planetary Ball Mill (type Fritsch P7) for Different Times (0.5-24h).). Microstructural and Structural Features of the Final Products Were Characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). the Results of the XRD Shows the Formation of the B2 (Ni Al) Phase after 2 Hours of Milling for both Systems. Also Detected Was the Ni₃al Phase in Ni₈₀al₂₀ after 4 Hours. Crystallite Size Refinement of the Final Product Occurred down to Nanometer Scales when the Milling Time Increased, and Attained 17 Nm in the Ni₅₀al₅₀ System and 20 Nm in the other System, at 24 Hours. this Decrease in Crystallite Size Is Accompanied by an Increase in the Interval Level Strain. the Kinetics of Al Dissolution during the Milling Process of Ni₅₀al5₀ System Can Be Described by Two Regimes, Characterised by Different Values of Avrami Parameters which Are Calculated by Using the Johnson–Mehl–Avrami Formalism.

Abstract: Oxide dispersion strengthened ferritic steels (so-called nanostructured ferritic alloys, NFAs), which are candidate structural materials in next generation nuclear power plant, have attracted much attention during recent years. In this work, iron oxide as oxygen carrier and titanium, yttrium hydrides were together mechanically milled with Fe-14Cr-3W gas-atomized powder. The thermal stability and recrystallization behaviour of the as-milled ferritic powder were studied by means of metallography, SEM, TEM and microhardness test. After ball milling for 48h, complete solid solution of bcc-Fe was formed in the as-milled powder. The thermal analysis results show that dispersed oxides with an average diameter of 5nm precipitate from the supersaturated matrix at about 850 °C. During annealing at temperatures from 800 to 1000 °C, a large number of equiaxed grains as fine as few hundreds of microns were found embedding in the matrix; the recrystallized grains stay quite stable and show minor dependence on annealing temperature and time. After being heated to 1200 °C for extended time, abnormal grain growth took place and resulted in bimodal grained structure. The effect of secondary particles on the thermal stability and recrystallization behavior of the ferritic steel was also discussed.

Abstract: The nanocrystalline silver powder and the amorphous powders of composition Ni49,5Ti20,5Nb15Zr15 (numbers indicate at%) were prepared by ball milling in the planetary Fritsch mill for 40 hours. TEM studies confirmed almost complete amorphization of milled alloys powders allowed to detect a small fraction of a small intermetallic inclusions within the amorphous matrix. The erosion of composites during contact cycling was similar as in Ag-W composites known as a good contact materials. SEM and TEM studies have shown a low solubility of tungsten in silver after ball milling and no solubility of silver in tungsten. The grain size of silver crystals within powders drastically decreased after milling down to about 30 nm and only a small increase in the grain size up to 200 nm was observed after hot pressing. These results were confirmed using TEM studies of composites after hot pressing. TEM microstructures have shown very narrow transition layer at the amorphous/silver interface (between 10-30 nm thick) containing all elements from the amorphous powders plus silver due to short time of hot pressing. The amorphous part has shown growth of intermetallic phases there, however diffused ring from the amorphous part was still visible. The composites prepared from silver and tungsten have shown presence of coherent tungsten rich precipitates showing typical strain field contrast within fine grains near 100 nm formed most probably during hot pressing of silver solid solution formed during mechanical alloying. The structure of tungsten has shown less defects and consequently less grain refinement than silver particles. SEM studies of the compression tested samples of silver-amorphous composites have shown crack formation at the interfaces of both components most probably due to presence of a brittle transition phase containing all elements.

Abstract: TiB2-TiC intermediate metal powder was fabricated via mechanical alloying (MA) processing, and the phase formation and powder morphology characteristics were studied by using X-ray diffraction（XRD）, scanning electron microscopy (SEM), differential thermal analysis (DTA). Starting materials were milled at ambient temperature in argon protective atmosphere. Prepared intermetallic phase of TiB2-TiC included, Ti3B4、Ti2B5、TiC0.06. Used milled powders prepare TiB2-TiC composition via two-way vacuum hot pressing sintering furnace not only decrease the time of preparation, but also reduce temperature of reaction, because of the preactivation reaction during MA promote the reactions. Therefore, this process will promote TiB2-TiC composite ceramics in engineering applications.

Abstract: Ti50Fe22Ni22Sn6 amorphous alloy is prepared by mechanical alloying and spark plasma sintering. The milling is performed in a high-energy planetary ball mill. XRD shows that after milled 70h, fully amorphous powders can be obtained, under the condition of the milling speed, 300rpm, and the weighs ratio of ball to powder, 10:1. Thermal stability of the as-milled amorphous powder is determined by DSC at the heating rate of 40K/min. The glass transition Tg and the initial crystallization temperature Tx1 is 625K and 770K, respectively. The amorphous alloy powder is compacted by spark plasma sintering at the temperature of 633K, 653K, 673K, 688K and 723K under the compress of 400Mpa. From XRD, it can be seen that near the glass transition temperature, the samples sintered remain completely amorphous, and when the sintering temperature increasing, although not higher than the initial crystallization temperature, the sintered samples have begun to appear crystalline phases.

Abstract: Cu-4% mixed-powder consisting of rough copper powder and graphite powder was separately mechanical alloyed by high-energy ball milling. The phases and micrograph of these powders were determined by X-ray diffraction and scanning electron microscopy (SEM). The results show an increase in the lattice parameter of copper with milling times, up to a saturation value of about 24h; There was an absence of graphite reflections from X-ray diffractograms after longer milling times.

Abstract: SrTiO₃ sample has been successfully prepared by mechanical alloying (MA) method. The effect of milling time on microstructure, crystallite size and dielectric properties of SrTiO₃ were studied. The results revealed that the mean crystallite size of milled powders decreased from 84.56 to 12.87 nm with increasing milling time. However, the average lattice strain of milled powders increased from 0.2 to 0.93% with increasing milling time. A single phase SrTiO₃ could not be formed with milling alone and required annealing process. A transformation of anatase-TiO₂ to rutile-TiO₂ was observed at 16 h of milling. After the milled powders were subjected to sintering process at 1200°C, formation of single-phase SrTiO₃-type cubic (Pm-3m) perovskite structure was observed. The peak intensities of the sintered SrTiO₃ samples decreased as the milling time was increased. For microstructural observations, the average grain size of the sintered SrTiO₃ sample milled for 8 h showed the largest. For dielectric measurements, the dielectric constant of the sintered SrTiO₃ sample milled for 8 h showed the highest among others. This could be due to the largest grain size obtained for sintered SrTiO₃ sample milled for 8 h. The decrease in the grain size with increasing milling time resulted to the decrease in dielectric constant.

Abstract: In this research, formation mechanism of a Cu/10 wt.% Cr-10 wt.% Al₂O₃ nanocomposite via mechanical alloying and subsequent heat treatment has been investigated. It was found that during milling process, Cu (Al) solid solution and Cu₉Al₄ phase were formed as intermediate products. Further heat treatment carried out under argon atmosphere at 900°C for 8 hours resulted in completion of Cr₂O₃ reduction by Al. The mechanism of in-situ formation of Al₂O₃ reinforcement in the copper matrix was also discussed as a two stages process. The SEM and TEM results confirmed the proposed mechanism and showed that the Cr dispersoids surrounded by Al₂O₃, in the nanometric scale. Also, the Cu matrix with mean crystallite size of 30 nm was stable at high temperature.