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

Abstract: High nitrogen nanostructured Fe-17Cr-11Mn-3Mo stainless steel powders were produced by high energy ball milling under a nitrogen atmosphere. It was found with increasing the milling time, the nitrogen contents of the powder mixtures increase linearly up to 1.98 wt pct after 96h, and a linear regression equation, WN = 0.19357 + 0.01887t , has been further established. In addition, with the increased milling time, the crystallite sizes and particle sizes of the powders decrease continuously, the lattice strains and sphericity of the powders increase gradually. After milling 60h, the high nitrogen nanocrystalline stainless steel powders with a fine particle size range of 5~10μm, excellent sphericity and uniform components can be obtained, whose crystallite size is about 5.0nm and lattice strain is about 1.0%. The powders milled for 60h was compacted using spark plasma sintering process at different temperatures. It is found that a fully austenitic high nitrogen stainless steel with almost full densification can be obtained by SPS at 1000°C, whose nitrogen content is 0.82 wt pct.

Abstract: Synthesis of intermetallic PbSe induced by high-energy ball milling has been studied. Systematic analysis of transformation in the resulting phases of milling from 0 to 10 h has been traced by characterizing the microstructures in terms of morphology, crystallite size, and percentages of phases formed as a function of milling time. Results reveal the formation of two phases. Where the system of PbO-Se transforms gradually to PbSe. Complete transformation is achieved after 10 h of milling time. Study of particle structure by the Rietveld Method further corroborates the value of the nano-order crystallite diameters as evaluated from the microscopic studies.

Abstract: To obtain intermediate temperature alloy solders with melting temperature of 400~600°C, (Ag-Cu28)-25Sn and (Ag-Cu28)-30Sn alloys were prepared by high energy ball milling. Ag-Cu-Sn nanocrystalline alloys have been obtained after milling for 40h. XRD results show that the (Ag-Cu28)-25Sn alloy consists of Ag4Sn and Cu3Sn, and the (Ag-Cu28)-30Sn alloy contains Ag4Sn, Cu3Sn and Cu6Sn5. The small polydispersed particles with size ranging from 1μm to about 25μm are observed from the (Ag-Cu28)-30Sn alloys milled for 40h by SEM. A large amount of small particles comprised of two or three grains are commonly observed by HRTEM, and average grain size is about 17.50nm. DSC results indicate that the melting points of the (Ag-Cu28)-25Sn and (Ag-Cu28)-30Sn alloys milled for 40h are 548.5°C and 539.3°C, respectively.

Abstract: Mechanical milled powders of boron nitride were obtained. The microstructural characterization of these milled powders was carried out using X-ray diffraction technique. Insights on the nature of the crystalline phases obtained in these milled powders were obtained between comparisons of theoretical and experimental X-ray diffraction patterns. Observations on the phase transformations have been carried out using calorimetry and thermogravity experiments. Morphological and microstructural characteristics of nanocrystals are obtained using SEM and HRTEM instruments.

Abstract: The reported work is on Ti-48Al-12Nb-1Cr (at %) system synthesized in a high-energy planetary ball mill with optimized milling parameters. The synthesized powders are characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD) and Differential Thermal Analysis (DTA) in order to understand the structural and phase transformation. The results obtained from the above said studies show the particles refinement, formation of non-equilibrium structures, etc. High-energy ball milling results super saturation of Al and Nb in titanium matrix at 15 hrs of milling, nanocrystalline nature at 20 hrs and amorphous phase formation at 50 hrs of milling. Differential Thermal Analysis (DTA) and XRD scans of MA powder thermally treated at 750°C for 1 hr show the formation of TiAl and TiAl3 intermetallic compounds.

Abstract: A large amount of the Ti6Si2B compound can be formed by mechanical alloying and subsequent heat treatment from the elemental Ti-22.2at%Si-11.1at%B powder mixture, but the yield powder after ball milling is reduced due to an excessive agglomeration of ductile particles on the balls and vial surfaces. This work reports on the structural evaluation of Ti-22.2at%Si-11.1at%B powders milled with PCA addition, varying its amount between 1 and 2 wt-%. The milling process was carried out in a planetary ball mill under argon atmosphere, and the milled powders were then heated at 1200oC for 1h under Ar atmosphere in order to obtain equilibrium structures. Samples were characterized by X-ray diffraction, scanning electron microscopy, and thermal analysis. Results revealed that the PCA addition reduced the excessive agglomeration during the ball milling of Ti-22.2at-%Si-11.1at-%B powders. After heating at 1200oC for 1h, the Ti5Si3, Ti3O and/or Ti2C phases were preferentially formed in Ti-22.2at%Si-11.1at%B powders milled with PCA addition, and the Ti6Si2B formation was inhibited.

Abstract: This work discusses on the structural evaluation of mechanically alloyed Ti-Nb powders. The Nb amount was varied between 20 and 50 wt-%. The milling process was carried out in a planetary Fritsch P-5 ball mill under Ar atmosphere. The structural evaluation was conducted by scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry. During ball milling it was noted an excessive agglomeration of ductile Ti-Nb powders on the balls and vial surfaces, and the final amount of remaining powders was then drastically reduced into the vials. This fact was more pronounced with the increased Nb amount in starting powders. Typical lamella structures were formed during ball milling, which were refined for the longest milling times, and fine and homogeneous structures were formed in Ti-Nb (Nb=20-50wt-%) powders. XRD results indicated that the full width at half maximum values of Ti peaks were continuously increased while that the crystallite sizes were reduced for longer milling times due to the severe plastic deformation provided during ball milling of Ti-Nb powders. However, the EDS analysis revealed the presence of Nb-rich regions in Ti-Nb powders after ball milling. The critical ball milling behavior of ductile Ti- Nb powders contributed for reducing the yield powder and increasing the structural heterogeneity.

Abstract: This work discusses on the effect of milling parameters on the TiB and TiB2 formation in Ti-50at%B and Ti-66at%B powders, respectively. Both powder mixtures were processed in a planetary ball Fritsch P-5 ball mill under Ar atmosphere, varying the milling parameters: rotary speed (150 and 200 rpm), size of balls (10 and 19mm diameter) and ball-to-powder weight ratio (2:1 and 10:1). In order to obtain the equilibrium structures the milled powders were heated at 1200oC for 1h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal analysis (DSC). XRD results indicated that extended Ti(B) solid solutions were formed during ball milling of Ti-50at%B and Ti-66at%B powders. After milling for 170h it was noted the TiB and TiB2 formation in Ti-50B and Ti-66B powders processed under higher-energy condition. DSC analysis revealed that the TiB2 formation was completed during heating of mechanically alloyed Ti-66at%B powders only. After heating at 1200oC for 1h, a large amount of TiB and TiB2 was found in Ti-B powders milled under higher energy condition.

Abstract: The main task of our work was to study the influence of high energy ball milling on the process of W-type hexaferrite material production and to compare the structural, morphological and magnetic features of the different manufacturing ways. The products are analyzed mainly by XRD, SEM and TEM methods. It was shown that high energy ball milling can be used to enhance the synthesis of W-type Ba-hexaferrite due to the much smaller crystallite sizes and their larger surfaces that are produced by the milling process and due to the activation of these surfaces.

Abstract: The comparison of the phase transformations going on due to high energy ball milling (HEBM) and produced by pressure-less Direct Metal Laser Sintering (DMLS developed by EOS company) was carried out, by using an α-Fe, Ni and Cu3P powder mixture. It could be shown by X-ray diffractograms (XRD) of the two type of products, that by mechanical alloying a similar phase transformation occurs due to solid state reactions between the metal partners as in the case of laser sintering, in a given range of laser scanning speed in a laboratory laser equipment. According to the XRD evaluation the same metastable, γ-steel like phases were formed.