First Hours Of Milling Research Articles

Effect of the high energy milling on the microstructure of Cu-20%WC composite powders prepared with recycled WC

A mixture of Cu-20wt%WC was milled in a high energy mill for up to 50 h. The WC powder was recycled from hard metal scrap. It presents agglomerates of faceted WC particles and residual Co and Fe. In the first hours of milling, the Cu particles are deformed into plates, the agglomerates of WC are broken apart, the primary WC particles are fragmented and embedded in the Cu phase. Composite particles are formed. As milling proceeds, different plates are welded together and folded. The particle size increases. However, the hardened Cu becomes fragile and begin to break, decreasing the particle size. Both, Cu and WC are under compressive strain. Residual Co and Fe present in the recycled powder are dissolved in Cu and behave like the soft Cu phase.

Mechanically Alloyed Composite Materials Based on the Al-Mg-Li System Strengthened by Oxides

Mechanical alloying in air atmosphere lead to interaction of an initial material with the oxygen with formation of strengthening oxide particles. It allows creating the dispersion strengthened composite materials. The possibility of obtaining the composite materials based on Al-Mg-Li alloys by mechanical alloying is shown. It was found that the most intense oxidation of the material held within the first hour of milling. Microstructure evolution and mechanical properties of composite materials is investigated.

Structural and magnetic properties of Co50Ni50 powder mixtures

In the present work, morphological, structural, thermal and magnetic properties of nanocrystalline Co50Ni50 alloy prepared by high energy planetary ball milling have been studied by means of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. The coercivity and the saturation magnetization of alloyed powders were measured at room temperature by a vibration sample magnetization. Morphological observations indicated a narrow distribution in the particle and homogeneous shape form with mean average particle size around 130μm2. The results show that an allotropic Co transformation hcp→fcc occurs within the three first hours of milling and contrary to what expected, the Rietveld refinement method reveals the formation of two fcc solid solutions (SS): fcc Co(Ni) and Ni(Co) beside a small amount of the undissolved Co hcp. Thermal measurement, as a function of milling time was carried out to confirm the existence of the hcp phase and to estimate its amount. Magnetic measurement indicated that the 48h milled powders with a steady state particles size have the highest saturation (105.3emu/g) and the lowest coercivity (34.5Oe).

Effect of the Milling Conditions on the Formation of Nanostructured Fe–Al Powders

Nanocrystalline Fe72Al28 alloy samples were prepared by the mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0-24 h range) by means of the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) and Mössbauer spectroscopy. The complete formation of bcc-FeAl solid solution is observed after 4 h of milling. The lattice parameter, a (nm), quickly increases within the first hours of milling and reaches a maximum value of 0.291 nm at 12 h of milling time; then a (nm) decreases to a value of 0.2885 nm for 24 h. The grain size decreases from 55 to 10 nm, while the strain increases from 0.18% to 0.88%. Grain morphologies at different formation stages were observed by SEM. The Mössbauer spectra show different behaviors with the increase of milling time. Indeed, after 4 h, the Mössbauer spectrum shows the presence of a singlet and sextet. The singlet indicates the presence of paramagnetic phase characteristic of A2 disordered structure and the sextet with a mean hyperfine field, , of 21 T is indicative of ordered DO3 structure. After 8 h of milling, the paramagnetic phase disappears leading to the appearance of a sextet, with a mean hyperfine field, Hhf, equal to 24.18 T which is characteristic of DO3’ structure. For the higher milling time i.e. 24 h, the Mössbauer spectrum was analyzed with two components. The first one with equal to 29.9 T is still indicative of ordered DO3, however, the second with a value of 10.25 T is characteristic of the fine domain B2 ordered structure.

The Influence of the Milling Media Environment on the Characteristics of a W-Cu Composite Powder

W-Cu composite powders were prepared by high energy milling under two milling environments: cyclohexane and air. Composite particles are formed in both cases. The W particles are fragmented and embedded into the Cu particles. Both, W and Cu, are heavily strained, mainly in the first hours of milling. The composite powder has high homogeneity and is much finer than the original Cu powder. The mean particle size of the powders milled in both conditions is very close, but the wet milling was near 25% longer than dry milling and the size distribution is wider. This is consequence of the higher milling intensity of dry milling.

Effect of the milling energy on the production and thermal stability of amorphous Mg50Ni50

The effect of milling energy on the amorphisation process and subsequent thermal crystallization of Mg50Ni50 was investigated. The amorphous Mg50Ni50 was produced using a planetary mill (medium energy) with a ball to material weight ratio of 13:1, and a SPEX mill (high energy) with a ball to material weight ratio of 20:1. The results obtained by means of X-ray diffraction showed that it is possible to obtain an amorphous Mg50Ni50 alloy, through both milling processes, starting of Ni powders and Mg turnings. However, the amorphisation process requires more time in the planetary mill (80–90 h) than in the SPEX mill (15–20 h), due to the difference in energy level and milling mechanism between these mills. The phase evolution during the amorphisation process is practically independent of the mill energy. In this way, it was observed that the mill conditions promoted an extensive refinement of the microstructure during the first hours of milling. The defects produced during this time led to the amorphisation of part of the system. This amorphous precursor suffers a mechanically induced crystallization into Mg2Ni, which is subsequently destabilized into amorphous Mg50Ni50. Based on the results obtained, it is proposed that the formation of amorphous precursor during mechanical milling of Mg and Ni is a characteristic of the Mg–Ni system, over a wide composition range, rather than of a particular composition. In relation to the thermal crystallization of the amorphous produced, the results of the differential thermal analysis applied to the amorphous samples showed that the formation enthalpy for both amorphous is the same, however, the amorphous produced in a planetary mill presented higher crystallization temperatures and apparent activation energies than the amorphous produced in a SPEX mill. The last behavior would be related with iron contamination coming from the erosion of the milling media. Finally, it is possible to conclude, that under the experimental condition employed, the amorphous phases produced in a planetary and SPEX mill, are structurally and energetically similar.

Structural and microstructural study of Fe–31Cr–12Co mixture prepared by ball milling

Nanostructured Fe–31Cr–12Co mixture was prepared by high energy ball milling (BM) of elemental Fe, Cr and Co powders. The obtained powders were characterized by X-rays diffraction (XRD) using Rietveld's method. The BM leads to the allotropic transformation of Co from FCC to HCP form during the first hour of milling and the formation of a disordered Fe(Cr, Co) solid solution (SS) with BCC structure after 12 h of milling. The microstructural analysis using the profile fitting shows the nanostructured character of the obtained powders. The diffraction line broadening of the SS is Miller indices dependent and is a consequence of anisotropy in size and strains.

Microstructural evolution during mechanical alloying of Mg and Ni

This study investigates the microstructural evolution during mechanical alloying of Mg and Ni, and during subsequent heat treatments of SPEX milled powders. The milling was performed under an inert argon atmosphere, employing two different ball-to-powder ratios (BPR): 10:1 and 20:1. It was observed that a large number of defects were produced during the first hours of milling. These defects led to the amorphization of part of the system, and promoted an extensive refinement of the microstructure as well. Later on, the formation of the Mg 2Ni compound due to the crystallization of the amorphous phase was observed. The microstructural details showed us that a possible complete sequence of phase transformations during milling of pure Mg and Ni could be: Mg c + Ni c → Mg nc + Ni c → amorphous + Ni nc + Mg nc → amorphous + Ni nc + Mg 2Ni nc → Mg 2Ni nc, where c and nc stand for crystalline and nanocrystalline, respectively. On the other hand, subsequent heat treatments of the milled powder showed that the amorphous phase could also be transformed into Mg 2Ni by heating. Finally, the knowledge of the evolution of the microstructure during milling and annealing were combined to propose an optimal processing route to efficiently obtain the Mg 2Ni compound.

M�ssbauer Study of Mechanically Alloyed Fe57Cr31Co12

Nanostructured powders of Fe 57 Cr 31 Co 12 were prepared by mechanical alloying from elemental Fe, Cr and Co powders, using a planetary ball mill type Fritsch Pulverisette 7. The powders were characterized by X-ray diffraction and 57 Fe Mossbauer spectrometry. A detailed analysis of the diffraction patterns reveals a decrease of the crystalline grain size as a function of milling time. For the first hours of milling, Mossbauer spectra are composed of a magnetic contribution and a single line. The paramagnetic component, whose relative area increases with milling time, can be attributed to paramagnetic Cr-rich clusters. The results are compared to those obtained on the same alloy prepared by conventional melting technique.

Mechanochemical Transformations in the Zinc-Magnetite System

Mixtures of magnetite and zinc powders were milled for up to 540 minutes and the development of the system was followed using X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. The process takes place in two overlapping steps. During the first hour of milling, a nonmagnetic intermediate mixed oxide phase forms which decomposes into ZnO and Fe upon further milling. The freshly formed iron particles are supersaturated with Zn.

On the formation of μ and ζ phases in the AgAl system by mechanical alloying

Pure Ag and Al powders have been mechanically alloyed in a Spex mill. Four selected nominal compositions Ag 1− x Al x ( x = 0.20, 0.23, 0.26 and 0.37) were investigated by X-ray diffraction and differential scanning calorimetry, after being subjected to different times of ball milling. In all four selected compositions, the close-packed hexagonal intermediate ζ phase and the f.c.c. α phase (Ag-based solid solution) formed together during the first hour of milling, but subsequently the α phase disappeared during continued milling except in the two alloys corresponding to 26 at.% Al and 37 at.% Al where the ζ phase is the equilibrium phase. With continued milling, the complex cubic μ phase formed in the alloys of nominal composition 20, 23 and 26 at.% Al where it is expected in equilibrium alloys. No amorphous phases have been observed in the mechanically alloyed powders in this system.

Cotton powder for infrared transmission measurements

Cotton cut in a Wiley mill to pass a 20-mesh screen was ground in a vibratory ball mill similar to one that has been used in Germany and Holland. Contamination of the cotton was practically eliminated by using a chromium-plated hardened steel jar and chromium alloy balls. The jar holder is held by a slip ring instead of being bolted in place. The jar and holder automatically rotate slowly on their axis, and this motion counteracts the tendency of the cotton in the jar to settle and grind nonuniformly. The jar is cooled by blowing air over it and becomes barely warm to the touch. Five grams of dried cotton disintegrated rapidly during the first 15 minutes of milling. The largest particles remaining after 30 minutes of milling were about 10 microns in major dimension, and there was little reduction of the maximum size with longer milling. Cuprammonium fluidity of the cotton increased rapidly in the first Hour of milling and more gradually thereafter. The carboxyl content of the cotton increased very slowly with time of milling and reached only about 0.2 percent after 8 hours. The moisture regain of the cotton at 65-percent relative humidity at 21° C increased rapidly during the first hour of milling, from 7.1 to 12.5 percent, and then remained practically constant. X-ray diffraction measurements showed that the cellulose was converted almost completely to the amorphous form in 30 minutes, and that it underwent little change thereafter. The powdered cotton obtained from the vibratory ball mill was mulled in mineral oil. The resulting paste was injected into rock salt cells for infrared absorption measurements. The powder worked reasonably well in this procedure, distinctly better than the coarse powders obtained by other methods of grinding. No significant differences were found in the infrared absorption of a regenerated cellulose film, the cotton ground in a Wiley mill to 200 mesh, and cotton ground in the vibratory ball mill for periods of time from 15 minutes to 8 hours. It is concluded that the vibratory ball mill, as modified, reduces cotton, rapidly and completely, to a very fine powder, suitable for infrared transmission measurements and other purposes. Milling results in practically negligible oxidation of the cellulose, but in a marked decrease in degree of polymerization, and in almost complete conversion of crystalline to amorphous cellulose.