Size Of Milled Powders Research Articles

Microstructural evolution in a new Fe based ODS alloy processed by mechanical alloying

Oxide dispersion strengthened (ODS) ferritic steels containing a high density of nanoscale clusters are produced by mechanical milling show excellent properties such as good irradiation swelling resistance and high-temperature creep strength. Mechanical milling with the aim of a fine dispersion of oxides dissolves in the matrix. The influences of process parameters during mechanical milling of ODS ferritic steels are important for material properties. In this research we investigated different milling time for the morphology and properties of powders. The results show that the powders by a stainless steel grinding media are experienced three stages: the mean powder size increases firstly then decreases. With the extending of the milling time, the mean powder size increases again. Otherwise the grain size decreases initially and then reach a saturation value. The grain size of milled powders was maintained in nanoscale range by TEM observation.

The effect of reinforcement percentages on properties of copper matrix composites reinforced with TiC particles

In this research, copper matrix composites reinforced with different amounts of titanium carbide particles were produced by mechanical milling and in-situ formation of reinforcements. Morphology and size of milled powders were inspected by scanning electron microscopy (SEM) several times during milling process. Changes in lattice parameter, crystallite size, lattice strain, dislocation density and Gibbs free energy changes (due to increasing in dislocation densities and grain boundaries) in different samples (with different TiC particles contents) were studied by X-Ray Diffraction technique with Cu-kα radiation and using Nelson–Riley method and Williamson–Hall equation. Microstructure of samples after sintering was investigated by FESEM. Finally, densitometry, hardness, determination of electrical resistance and pin on disk wear test were performed and effect of reinforcement percentages on the physical and mechanical properties of composites was studied. Results show incredible improvement in mechanical properties with increasing in TiC value, even though, electrical conductivity dropped off considerably.

Experimental investigation on the compressibility of Al/Al<SUB align="right">2O<SUB align="right">3 nanocomposites

The scientific importance of nanocomposites is being increased due to their improved properties. This paper introduces an experimental investigation on the relationship between the reinforcement weight fraction and compressibility of Al/Al2O3 during high energy ball milling. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterise the produced powder. The results showed that the grain size of milled powders was about 43 nm with a noticeable presence of agglomerates at 10 wt.% of Al2O3. By increasing Al2O3 weight fraction to 12% the decrease in grain size was very. With up to 12 wt.% of Al2O3, microhardness increases from 62 to 150 HV due to the decrease of the crystallite size. The compressibility behaviour of the nanocomposite powder was decreased slowly by increasing Al2O3 content due to work hardening on the matrix powder.

Preparation and Characterization of Al Matrix Composites Reinforced with (20-x) wt.-% Al2O3 - (x) ZrO2

Metal matrix nanocomposites composed of Al-(20-x) wt.-% Al2O3 - (x) ZrO2, x=0, 1, 2 & 4, were prepared by mechanical alloying technique. The powders’ mixture was milled in a planetary ball mill up to 7h. The effect of milling time on properties of obtained powders was studied by using X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) to investigate phase composition, crystal size and morphology of the milled powders. In order to study the sinterability, the milled nanocomposite powders were cold pressed and sintered in argon atmosphere at different firing temperatures i.e. 300, 370 and 470°C for 1h. Physical properties, namely, bulk density and apparent porosity of sintered bodies were determined by Archimedes method. Phase identification and microstructure of the sintered composites were investigated by using XRD and scanning electron microscope (SEM) as well as energy dispersive spectrometer (EDS). Microhardness of sintered composite was also examined using Vickers hardness indentor. The results were discussed in terms of the effect of milling time on the properties of the prepared powders and sintered composites. The results revealed that the grain size of milled powders was about 30 nm with a noticeable presence of agglomerates. Uniform distribution of nano-sized alumina-zirconia particles in the aluminum matrix could be achieved with increasing milling time. The density of the sintered composites was affected by milling time of starting powders and firing temperature. It increased with increasing milling time and firing temperature. Microhardness of sintered bodies was found to be progressively increased with increasing of milling time of starting powders.

A novel method for the production of metal powders without conventional atomization process

Fabrication of Al alloy powders from recycling chips by mechanical milling is a novel processing technique. In this study, the mechanical milling was applied to the production of AA7075 powders from the recycling chips. The effect of milling time on the morphology, particle size and powder yield of the milled chips and fabricated powders was investigated. Fabricated powders were characterized by a scanning electron microscope (SEM), a Laser Particle Size Analyzer, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). A chip milling model based on the morphology and size of milled powders were presented. It was found that after 10 h of milling, the average particle size of the AA7075 powders was reduced to 35 μm. Results showed that 5 h of milling was the critical milling time in a change in the chip morphology (segmented shape) from powder morphology (irregular shape). The particle size of fabricated powders after 10 h of milling was about 286 times lower than that of initial chips.

Effect of Mechanical Milling on the Morphologyand Structural Evaluation of Al-Al2O3 Nanocomposite Powders

The morphological and microstructural changes during mechanical milling of Al powder mixed with 2.5, 5 and 10 wt.% Al2O3 particles were studied. The milling was performed in a planetary ball mill for various times up to 20 h. The produced composite powders were investigated using X-ray diffraction pattern (XRD) to elucidate the role of particle size, secondary phase content and milling time on grain size and lattice strain of Al matrix. The aluminum crystallite size estimated with broadening of XRD peaks by Williamson–Hall formula. To investigate the morphological changes by the scanning electron microscopy (SEM) analysis. The results show that the addition of hard Al2O3 particles accelerates the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Furthermore, Al becomes smaller crystallite size during ball milling of Al powder in the presence of Al2O3 particles. The results revealed that the grain size of milled powders was about 45 nm with a noticeable presence of agglomerates. Uniform distribution of nano-sized Al2O3 particles in the Al matrix could be achieved with increasing milling time.

Preparation by mechanical alloying, characterization and sintering of Cu–20 wt.% Al2O3 nanocomposites

Metal-matrix nanocomposite, composed of copper/20wt.% Al2O3, was fabricated by mechanical alloying method. The starting powders mixture was milled in planetary ball mill up to 20h. The effect of milling time on the properties of the obtained powders was studied. X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were used to investigate phase composition, crystal size and morphology of the milled powders. To study the sinterability, the milled nanocomposite powders were cold pressed and sintered in argon atmosphere at different firing temperatures, i.e. 700°, 800° and 850°C, for 1h. Physical properties, namely, bulk density and apparent porosity of sintered bodies were determined by Archimedes method. Phase identification and microstructure of the sintered composites were investigated by using scanning electron microscope (SEM) as well as energy dispersive spectrometer (EDS). Microhardness of sintered composite was also examined using Vickers hardness. The results were discussed in terms of the effect of milling time on the properties of the prepared powders and sintered bodies. The results revealed that the grain size of milled powders was about 55nm with a noticeable presence of agglomerates. Uniform distribution of nano-sized alumina particles in the copper matrix could be achieved with increasing milling time. The density of the sintered composites was affected by milling time of the starting powders and firing temperature. It increased with increasing milling time and firing temperature. Microhardness of the sintered bodies was found to be progressively increased with increasing of milling time of starting powders.

Effects of mechanical alloying on characteristics of nanocrystalline Fe–Cr–W–Ti–Y 2O 3 powders

Effects of mechanical alloying (MA) parameters on characteristics of nanocrystalline Fe–Cr–W–Ti–Y 2O 3 powders, including alloying degree, grain size, microhardness and morphology had been systematically investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the alloying degree of milled powders was increased with the elevation of milling rotational speed and elongation of milling duration. The W atoms were completely dissolved into the iron matrix after milling at 350 rpm for 24 h. The grain size of milled powders was decreased sharply at first stage of milling and leveled off after 24 h, while lattice strain was increased. The microhardness of alloyed powders was elevated firstly and stabilized at about 607.4 HV after 24 h milling. Process control agent (PCA) effected the morphologies and retarded the alloying extent of the milled powders. Finer, more uniform and spherical particles were obtained when steric acid (SA) was chosen as PCA. Increasing ball to powder ratio (BPR) would lead to efficient reduction of average particle size, but decrease powder yield and increase contamination.

Evolution of microstructure in MgH2 powder particles during high energy ball milling and hydrogen cycling

Abstract We investigated in details the evolution of microstructure by electron microscopy when powder MgH 2 particles were ball milled up to 60 h. The average particle size reduced to less than 5 μm within 5 h of milling from an average size of 38 μm measured before milling. The grain size reduced from an average of ∼750 nm in the un-milled powder to below 100 nm after milling. Particle size, as well as the grain size of milled powders followed log-normal distribution. Lattice strain was introduced significantly in the milled powder as a result of milling. Upon hydrogen cycling, this strain was reduced and the grain size was increased.

Structural evolution of mechanically alloyed nanocrystalline FeAl intermetallics

Nanostructured FeAl intermetallics were prepared directly by mechanical alloying (MA) in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during mechanical alloying were investigated by X-ray diffraction (XRD). Transmission electron microscopy (TEM) was employed to examine the morphology of the powders. Thermal behavior of the milled powders was examined by differential scanning calorimetry (DSC). Disordered Fe(Al) solid solution was formed at the early stage. After 30 h of milling, Fe(Al) solid solution transformed into an ordered FeAl phase. The average crystallite size reduction down to about 12 nm was accompanied by the introduction of the average lattice strain up to 1.7%. The TEM picture showed that the size of milled powders was less than 30 nm.

Nano-amorphous (FeAl) 1− xZr x alloys prepared by mechanical alloying

Nano-amorphous (FeAl) 1− x Zr x ( x = 20, 33.3) alloys have been prepared by mechanical alloying. The microstructure, morphology and thermal stability of as-milled powders were analyzed by XRD, TEM and DTA, respectively. The size of milled powders was smaller than 50 nm. The thermal stability of as-milled powders decreased with increment of Zr. The products of crystallization for milled powders annealed at temperature over the crystallization temperature were also investigated. The effective activation energies for crystallization are evaluated according Kissinger's plot. The composition range of amorphous (FeAl) 1− x Zr x was predicted from Miedema's theory and a geometric model.