Papers by Keyword: Mechanical Milling

Abstract: Nd2Fe14B/α-Fe nanocomposite powders with a nominal composition of Nd12Fe82B6 were prepared by HDDR combined with mechanical milling. The microstructure of both the as-disproportionated and the subsequently desorption-recombination annealed alloy powders was studied by Mössbauer spectrometry and TEM. The magnetic properties were investigated by VSM using bonded magnet samples. The results showed that the annealing temperature had significant influence on both the recombination kinetics and the grain size of the Nd2Fe14B/α-Fe nanocomposite phases, and the bonded magnet samples presented the best magnetic properties when the nanocomposite powders were prepared by annealing at 760°C for 30 min.

Abstract: Lithium is one of the active metals and reacts with nitrogen even at room temperature. In this study, in order to grind and activate Li, the mechanical milling of Li with stable metal oxide, namely, Al2O3 and MgO, using a high energy vibrating ball mill was performed. In the case of Li- MgO system, it reacts with N2, but hardly reacts with O2. The reaction with N2 generally produces Li3N, while for some vigorous reactions the Mg3N2 and Li2O are produced as the major phases. In the case of Li-Al2O3 system, however, reactivities with both N2 and O2 are high. The difference will be explained in terms of the reaction mechanism and the Li state.

Abstract: In present work, manufacturing technologies of titanium hydride powder were studied for recycling of titanium tuning chip and for this, attrition ball milling was carried out under H2 pressure of 0.5 MPa. Ti chips were completely transformed into TiH2 within several hundred seconds that is very short time comparing to that in the previous report. Dehydrogenation process TiH2 powders is consist of two reactions: one is reaction of TiH2 to TiHx and the other decomposition of TiHx to Ti and H2. The former reaction shows relatively low activation energy ranged from about 100 KJ/mol to 250 KJ/mol and it is suggested that the reaction is caused by introduction of defects due to milling. In case of TiH2 powders that hardly contains defects, decomposition of TiH2 to Ti and H2 occurs directly without the reaction of TiH2 to TiHx and activation energy is very large as much as 929 KJ/mol.

Abstract: Ti(Al,O)-Al2O3 composite powders were produced by high energy mechanical milling of a mixture of Al and TiO2 powders followed by combustion reaction. The powders were then thermally sprayed on H13 steel substrates. Microstructural examination was conducted on the composite powders and thermally sprayed coatings using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The performance of the coatings was evaluated in terms of microhardness and thermal fatigue. The thermally sprayed coatings showed fairly good performance in the preliminary thermal fatigue tests and did not display any wetting tendency to molten aluminum.

Abstract: The influence of the Co addition and synthesis route on desorption properties of MgH2 were investigated. Ball milling of MgH2-Co blends was performed under Ar using different milling intensities and different weight ratios. Microstructural and morphological characterization, performed by XRD and SEM, show a huge correlation with thermal stability and hydrogen desorption properties investigated by DSC. A complex desorption behaviour is correlated with the dispersion of the catalytic particles that appears to play a main role in desorption performances. The optimum catalyst concentration was found to be around 10 wt.%, while the optimum value of the ball to powder ratio was 10:1.

Abstract: The Zincalume hot-dip coating process is a well-established technique for excellent corrosion protection of steel products. This paper describes the study of two intermetallics based on the Fe- Al-Si-Zn alloy system, α-AlFeSi and α-AlFeSi(+Zn), pertinent to the Zincalume process. These intermetallics are difficult to characterize in-situ due to their formation at high temperature and because they form as very thin intermetallic layers on a steel substrate, which inhibits accurate quantitative analysis. Controlled magneto-ball milling and hot-pressing have been employed in an attempt to synthesise these intermetallic compounds. Magneto-ball milling, under a He atmosphere, was conducted in shearing mode to enable controlled milling of elemental powders, namely Zn and Al, without the excessive cold-welding often associated with milling of ductile powders with high coefficients of surface friction. XRD analysis indicated that uniform mixtures of highly reactive fine-structured powders were produced, as indicated by diffuse elemental peaks of low intensity. Hot-pressing was utilized to sinter the powders into compact intermetallic compounds without sintering aids. The intermetallics were characterized by DTA, XRD and elemental contrast mapping performed on an SEM with EDS.

Abstract: A study has been carried out on the grain size distribution of cylindrical compacts obtained by consolidation of iron powder severely deformed by mechanical milling. Consolidation has been performed in two consecutive steps: cold and hot conditions. The hot one was done at two temperatures, namely 425 and 475°C. After milling, the iron powder has a grain size of 8 nm (± 4 nm) with an average hardness of 800 HV. After hot compaction the grain size increases up to 50 nm, especially at 475°C where a small fraction of grains reach larger values than the average. The grain size was evaluated by two different techniques, X-Ray Diffraction and Transmission Electron Microscopy. Results showed some differences between both methods. The advantage of using TEM is that grain size distribution, and not only the average size, can be obtained. Small discs were also obtained from the compacted specimen in order to fracture them on a “ball on three balls” equipment. The fracture behaviour of the samples was then studied by SEM.

Abstract: The limit of dislocation density was investigated by means of mechanical milling (MM) treatment of an iron powder. Mechanical milling enabled an ultimate severe deformation of iron powder particles and dislocation density in the MM iron powder showed the clear saturation at around the value of 1016m-2. On the other hand, the relation between hardness and dislocation density was examined in cold-rolled iron sheets, and the linear Bailey-Hirsch relationship; HV[GPa]=0.7+3×10-8ρ1/2 was obtained in the dislocation density region up to 3×1015m-2. Extrapolation of the Bailey-Hirsch relationship indicated that the dislocation strengthening should be limited to about 3.7GPa in Vickers hardness which corresponds to about 1.1GPa in 0.2% proof stress.

Abstract: Mechanical milling (MM), which is one of SPD process, is applied to W powder and W-Remixed powder. MM processed W and W-Re powders easily form nano grain structure even though they have high melting temperature. The nano grain formation mechanism in these powders is as follows: multi axial deformation of the powders by milling, at the temperature of 333K at most, produces pan-cake grain structure at first. Extremely dense dislocations result in grain sub-division, and finally nano grain structure with high angle boundary forms. Nano grains with approximately 10 nm in diameter are obtained. The MM powders are sintered using Spark Plasma Sintering process. Sintering and high temperature deformation behaviors of the MM powders are also investigated. The MM treatment enables W powder to be able to sinter at 1273 K while the powder without MM could never sintered at the same temperature. Re addition prevents grain growth during sintering and thus increases hardness of the compacts. A large deformation of W-10mass%Re sintered compact, whose grain size is approximately 450nm, is observed at elevated temperatures.