Milled Powder Mixture Research Articles

Prenucleation effect on characterisations of synthesised nanocrystalline tungsten carbide via mechanical milling

Monotungsten carbide was successfully synthesised in two systems using raw powders of W–C and W–C–WC measured in the nanometre scale. These materials were separately milled using a high energy ball mill and sampled frequently. The microstructures and composition of the as milled powder mixture were detected by SEM, TEM and X-ray diffraction. The results showed that adding 1 wt-%WC to the raw materials leads to the production of monotungsten carbide during the milling process. The size of the synthesised carbide crystalline (measured in nanometre) was reduced in proportion to the increase in milling time, while, at the same time, the mean lattice strain was increased. Furthermore, when the milling times increased, a considerable amount of iron in the form of amorphous dissolved into lattice as impurity. This reduced the density of milled powders, as well as the shrinkage of tungsten and tungsten carbide unit cells. Owing to the development of agglomerates during the milling process, the rate of change in specific areas was not consistent with the change in the size of particles.

Mechanosynthesized and ultra-fast quenched AgI–Ag2O–B2O3 materials with high AgI contents

Abstract The 78AgI, 16.5Ag2O, and 5.5B2O3 mol% powder mixture, ultra-fast quenched 78AgI-16.5Ag2O-5.5B2O3 glass containing α-AgI crystalline precipitates and pristine AgI were ball-milled at a high rotation speed. For all the materials, the processing did not cause formation of α-AgI phase, in contrary, it prompted α to β phase transition of the α-AgI precipitates in the glass. Nanosize scale β/γ-AgI grains were detected both in the milled powder mixture and in the glass but not in the pristine AgI powder. The decrease of α to β phase transition temperature was observed for the milled materials during cooling from 170 °C, ca. 10 °C, 60 °C and 75 °C respectively for the AgI powder, the powder mixture and the glass. Stabilization of the α-AgI to low temperatures was related to the nanosize scale β/γ-AgI grains. The work demonstrates, that although it is not possible to stabilize α-AgI in pure silver iodide powder by ball-milling, nevertheless it is achievable for mixtures with high AgI contents.

Characterization of nano-structured Cu–6 wt.% Zr alloy produced by mechanical alloying and annealing methods

The mechanical alloying process is used to produce nano-structured solid solution alloys, which may be further strengthened by the age-hardening process. Milling time is an important parameter during mechanical alloying. In the present research, the optimum milling time for the production of Cu–6wt.% Zr alloy was to be determined. Cu and Zr powder mixtures were milled in a planetary ball mill for different milling times. As milled powder mixtures were investigated by SEM and XRD. Average particle sizes, lattice parameter and average crystal size were determined at different milling times. As milled powder mixtures were subsequently isothermally annealed at different temperatures and their microhardness was measured. The results showed that during milling, average particle size initially increased to a maximum value and decreased at longer times, while average crystal size continuously decreased with milling time. Lattice parameter increased with milling time. The maximum hardness value was obtained after 48h of milling and annealed at 600°C. Longer milling times did not improve hardness of the material.

Microstructural Evolution and Mechanical Properties of a Multicomponent Nb-16Si-22Ti-2Al-2Hf-2Cr Alloy Prepared by Reactive Hot Press Sintering

In this paper, the effect of reactive hot press sintering (RHPS) parameters, such as milling time, hot pressing temperature, and heat treatment, on phase constitution, microstructure, and room temperature mechanical properties of a multicomponent Nb-16Si-22Ti-2Hf-2Al-2Cr alloy prepared from ball milled powder mixture is investigated. Evaluation of the microstructure revealed that all as-sintered and heat-treated samples mainly consisted of particles of Nb and Ti solid solutions (NbSS and TiSS), as well as a niobium silicide β-Nb5Si3 matrix, with a small quantity of Hf solid solution particles (HfSS). By sintering at 1773 K and 1873 K (1500 °C and 1600 °C), most of the NbSS phase in the samples prepared from 5 and 10 ball milled powder mixtures showed a narrow strip morphology. Upon increasing the milling time to 20 hours, the morphology changed to a near-equiaxed shape, which became finer with increased milling time. In contrast, the TiSS phase in all as-sintered samples more or less had a near-equiaxed shape. Spheroidizing tendency took place in both NbSS and TiSS phases during an annealing heat treatment at 1773 K (1500 °C) for 50 hours. Interestingly, when the milling time was extended from 5 to 20 hours, the volume fractions of the β-Nb5Si3 and TiSS phases increased, whereas that of the NbSS phase decreased. This resulted in the reduction of the fracture toughness KQ and an enhancement of the Vickers hardness Hv of the bulk as-sintered and heat-treated samples. A fractography analysis was also carried out to elucidate the fracture behavior of phases, with particular emphasis on the interaction between phases and cracks.

High temperature synthesis of single-phase Ti3Al intermetallic compound in mechanically activated powder mixture

Abstract The influence of the duration of preliminary mechanical activation on the microstructure of the powder mixture of 3Ti + Al and the features of the kinetics of the thermal explosion processes in milled powder mixtures were studied. It was shown that the formation of highly defective crystalline structures with high curvature of the lattice and high internal stress gradients took place with the increase of milling time. It was found that the features of heating during the thermal explosion process were determined by the features of the microstructure of the milled mixture. As a consequence, the composition of the product depended on the milling time and also on the heating rate of the mixture by the external heating source. Thus, the milling time and the heating rate can be considered as the control parameters in the research. The reacting system turned into the stable mode of phase formation characterized by the formation of mechanocomposites with the increase of milling time. The process was accompanied by the decrease in the effective activation energy of the synthesis down to the anomalous low value. The modes of the synthesis realization were determined to obtain a strictly single phase compound Ti 3 Al. It was hypothesized on the transition of the process from the diffusion regime of phase formation to the kinetic one with milling time.

Mechano-Chemical Synthesis of TiB<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> Nano-Composite by Reaction between TiO<sub>2</sub>, B<sub>2</sub>O<sub>3</sub> and Al

In this research a composite structure containing of a TiB2 matrix with dispersed Al2O3 particles was obtained via mechanical alloying of Al, TiO2 and B2O3 powder mixture. The mixture was milled for different lengths of time. Phase evolutions of the milled powder mixture were investigated. Powder particle characteristics were evaluated by XRD, SEM and TEM techniques. The XRD results reveal that the reaction begins during first 10 h milling by formation of TiB2 and Al2O3¬ phases and further milling causes partial amorphization of powder mixture. SEM micrograph of the sample milled for 30 h exhibited ultrafine particles of Al2O3-TiB2, but TEM images show that particles consist of some grains in the range of nano-size. The mean crystallite size of final product is about 25 nm.

In Situ Production of Fe-TiC Nanocomposite by Mechanical Activation and Heat Treatment of the Fe2O3/TiO2/C Powder

In this study, Fe-TiC nanocomposite was synthesized by carbothermic reduction of activated Fe2O3, TiO2, and graphite powder mixture. The effect of 0, 5, and 20 h of high energy ball milling of mixture on the reduction process was also investigated. Comparing the results of the thermogravimetry analysis of milled and un-milled mixtures clearly showed that the reduction temperature decreased due to the milling process. XRD pattern of 20 h milled powder mixture proved that Fe-TiC nanocomposite was formed after the heat treatment of activated powder at 1100°C for 1 h under vacuum. The microstructure studies of the milled mixture by scanning electron microscope revealed homogenous distribution of TiC particles in the Fe matrix.

Mechanical Properties of Hot-Pressed Compacts Made by Alumina Particle Dispersion Magnesium Powders

To enhance the mechanical properties of Mg alloys, powders of pure Mg (Al2O3/Mg) dispersed with over 10 vol% Al2O3 particles were formed by ball milling powder mixtures of pure Mg and Al2O3 particles with particle sizes of 0.3 and 1 μm. The effect of the Al2O3 content of hot-pressed discs of Al2O3/Mg powders on the mechanical properties was investigated. The hardness increased sharply at certain Al2O3 content. This is considered to be because of the development of Al2O3 particle strengthening due to the excellent interfacial bonding between Mg and Al2O3 particles when the Al2O3/Mg discs contain a sufficient amount of Al2O3 particles and have a sufficient interparticle distance. The maximum hardness was 220 HV. The tensile strength increased as Al2O3 content was increased. The Al2O3/Mg plate with Al2O3 particles sizes of 0.3 and 1 μm indicated maximum values of the bending strength at 10 and 14vol%Al2O3 content, respectively.

Characterisation of mullite – ZrO2 ceramics prepared by various methods

Mullite – ZrO2 ceramics was sintered from variously prepared powder mixtures -different time milled and hydrothermal synthesized. As sintering aid 8 wt. % illite clay for one part of starting mixtures was added. Two sintering routes was applied for consolidation of powder – spark plasma sintering (SPS) technique and conventional sintering reactions in air. It is shown that the structure of sintered samples for SPS was completed at 1250°C and by conventional - at 1300°C. The developed microstructure both conventional and SPS can be characterized by mullite matrix with evenly distributed ZrO2 grains. For conventionally prepared and sintered samples corundum and ZrO2 tetragonal grains are observed, but for SPS dominates ZrO2 cubic. The microstructure of ceramic samples from hydrothermal synthesized powders and consolidated by SPS is amorphous like, with xenomorfic crystals of mullite and inclusions of ZrO2 cubic grains. It is stated that additive of illite clay promotes the densification. At conventional sintering clay prevents the transformation of ZrO2 tetragonal to ZrO2 monoclinic by cooling of samples, but for SPS promotes formation of ZrO2 cubic. SPS sintered samples processed from conventionally milled powder mixture are characterized by pressure strength.

Role of intensive milling in mechano-thermal processing of TiAl/Al2O3 nano-composite

In this research a nano-composite structure containing of an intermetallic matrix with dispersed Al2O3 particles was obtained via mechanical activation of TiO2 and Al powder mixture and subsequent sintering. The mixture has been milled for different lengths of time and then as a subsequent process it has been sintered. Phase evolutions in the course of milling and subsequent sintering of the milled powder mixture were investigated. Samples were characterized by XRD, SEM, DTA and TEM techniques.The results reveal that the reaction begins during milling by formation of Al2O3 and L12 Al3Ti and further milling causes partial amorphization of powder mixture. DTA results reveal that milling of the powder mixture causes solid state reaction between Al and TiO2 rather than liquid–solid reaction. Also, it was observed that the exothermicity of aluminothermic reduction is reduced by increasing the milling time and the exothermic peak shifts to lower temperatures after partial amorphization of powder mixture during milling. Phase evolutions of the milled powders after being sintered reveal that by increasing the milling time and formation of L12 Al3Ti in the milled powder, intermediate phase formed at 500°C changes from D022 Al3Ti to Al24Ti8 phase.

Nanostructure Cu–Cr alloy with high dissolved Cr contents obtained by mechanical alloying process

A nanostructural solid solution of Cu–Cr was prepared by the mechanical alloying process. Three mixtures of Cu powders with 1, 3 and 6 wt-%Cr powders were milled under 250 rev min−1 for different milling times of 4, 12, 48 and 96 h. The mixtures were subsequently compacted and sintered at 450, 600 and 750°C for half an hour. Milled powder mixtures were examined by X-ray diffraction technique, which showed the presence of nanoscale crystallites in the samples and the decrease of lattice parameter of Cu crystals. Sintered powders were investigated by optical microscope and their hardnesses were measured by microhardness. Results showed increasing trends in hardness of the compacted powder mixtures with increasing milling time. Sintering temperature had also evident effects on the behaviour of powder mixtures. As sintering temperature increased, microhardness increased and a peak appeared then a decreasing trend was observed.

Fabrication of TiB2-(Fe-Al) Cermets by Short Time Pulsed Current Sintering

Short time fabrication of TiB2-30mass% Fe3Al cermet was performed by pulsed current sintering method. Milled powder mixture of TiB2, Fe and Al was consolidated using a pulsed current of 0 A-1000 A with 50 % duty ratio for 50 s with 1, 10 and 100 Hz frequency. Microstructures, densities and phases present in the cermets fabricated in such a way were examined. TheTiB2-30mass% Fe3Al cermet without formation of Fe2B was successfully fabricated. Increase in the pulse frequency led to an increase in the sample density and homogeneous distribution of TiB2 particles.

アルミナ粒子分散マグネシウムの機械的性質に及ぼすアルミナ含有率の影響

To enhance the mechanical properties of magnesium (Mg) alloys, powders of pure Mg (A1 2 03/Mg) dispersed with over 10 vol% alumina (Al 2 O 3 ) particles were made by ball milling powder mixtures of pure Mg and Al 2 O 3 particles with particle sizes of 0.3 and 1 μm. The effect of the Al 2 O 3 content of hot-pressed discs formed from the A1 2 03/Mg powders on the mechanical properties of the discs was investigated. The Al 2 O 3 particles were found to be uniformly dispersed in the Al 2 O 3 /μg discs. The hardness of the discs increased sharply at an Al 2 O 3 content of 20vol%. This is considered to be because of the excellent interfacial bonding between Mg and A1 2 0 3 when the Al 2 O 3 /μg discs contain a sufficient amount of A1203 particles and have a sufficient interparticle distance. The maximum hardness of a 20vol% Al 2 O 3 /Mg disc (with an Al 2 O 3 particle size of 0.3 μm) was 220 HV, which is much higher than the hardness of AZ91 Mg alloys. The bending strength of the A1 2 03/Mg discs increased from 0 to 10vol% Al 2 O 3 and then decreased from 20vol% Al 2 O3. It is considered that the 0 and 10vol% discs have similar fracture deflections and that the 10 vol% discs with Al 2 O 3 particles can withstand higher compression and tension forces than the 0 vol% discs which do not contain any particles. The reason for the lower bending strength of the 20 vol% Al 2 O 3 disc is thought to be because it is harder and more brittle, making it easier for voids to form in the discs, and thus making it easier for cracks to propagate on the specimen surface.

Determining aroma‐active compounds in Kama flour using SPME‐GC/MS and GC–olfactometry

AbstractKama flour is a traditional Estonian food, consisting of a newly milled powder mixture of roasted barley, rye, wheat and pea flour. For consumption it is normally mixed with sour milk and sweetened with sugar. In this study the aroma profile of Kama flour was studied. For the analysis, the solid‐phase microextraction (SPME) method was optimized and used in combination with gas–chromatography/mass spectrometry (GC/MS) and GC–olfactometry (GCO), where the human nose is used as a sensitive and specific detector for odour‐active compounds. For a positive identification of the aroma‐active compounds, calculation of retention indices combined with the odour impression of pure reference compounds in a comparable concentration, and the mass spectrum under the same conditions as GC‐O were used. The analysis of Kama flour headspace by GC/MS led to the detection of 89 compounds, of which 62 were found to have odour impression according to the literature. However, in total, 30 odour‐active compounds were detected with GCO from which seven could not be detected under the same chromatographic conditions either by GC/MS or GC with FID. Most of the identified aroma compounds belonged to pyrazines coming from roasting process of Kama flour due to the Maillard reaction. Additionally, 2,3‐butadedione, hexanal and 1‐octen‐3‐one contributed to the aroma of Kama flour. Copyright © 2010 John Wiley & Sons, Ltd.

Mechanochemical assisted synthesis of B 4C nanoparticles

The present work reports on the preparation of boron carbide nanoparticles by the reduction of boron oxide with magnesium in the presence of carbon using the mechanochemical processing. The phase transformation and microstructure of powders during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during ball milling the B 2O 3–Mg–C reacted with a self-propagating combustion mode producing MgO and B 4C compounds. To separate B 4C from the milled powder mixture, an appropriate leaching process was used. After leaching, the purified powder mixture was characterized using XRD and transmission electron microscope (TEM). XRD studies indicated that the prepared particles were single phase crystalline B 4C. Moreover, TEM studies showed the size of B 4C particles were ranging from 10 to 80 nm.

Effect of Alumina Content on the Mechanical Properties of Alumina Particle Dispersion Magnesium

To enhance the mechanical properties of magnesium (Mg) alloys, powders of pure Mg (A1 2 03/Mg) dispersed with over 10 vol% alumina (Al 2 O 3 ) particles were made by ball milling powder mixtures of pure Mg and Al 2 O 3 particles with particle sizes of 0.3 and 1 μm. The effect of the Al 2 O 3 content of hot-pressed discs formed from the A1 2 03/Mg powders on the mechanical properties of the discs was investigated. The Al 2 O 3 particles were found to be uniformly dispersed in the Al 2 O 3 /μg discs. The hardness of the discs increased sharply at an Al 2 O 3 content of 20vol%. This is considered to be because of the excellent interfacial bonding between Mg and A1 2 0 3 when the Al 2 O 3 /μg discs contain a sufficient amount of A1203 particles and have a sufficient interparticle distance. The maximum hardness of a 20vol% Al 2 O 3 /Mg disc (with an Al 2 O 3 particle size of 0.3 μm) was 220 HV, which is much higher than the hardness of AZ91 Mg alloys. The bending strength of the A1 2 03/Mg discs increased from 0 to 10vol% Al 2 O 3 and then decreased from 20vol% Al 2 O3. It is considered that the 0 and 10vol% discs have similar fracture deflections and that the 10 vol% discs with Al 2 O 3 particles can withstand higher compression and tension forces than the 0 vol% discs which do not contain any particles. The reason for the lower bending strength of the 20 vol% Al 2 O 3 disc is thought to be because it is harder and more brittle, making it easier for voids to form in the discs, and thus making it easier for cracks to propagate on the specimen surface.

Effects of copper and Al 2O 3 particles on characteristics of Cu–Al 2O 3 composites

High-energy milling was used for production of Cu–Al 2O 3 composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al 2O 3 powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al 2O 3 particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al 2O 3 particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al 2O 3 particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al 2O 3 composites.

Preparation of ultrafine WC-Co cermets by combining pretreatment and consolidation with spark plasma sintering

Ultrafine-grained WC-Co bulk materials were prepared by a new method that contains pretreatment of the milled powder mixture and subsequent spark plasma sintering (SPS). Ball milling parameters and the pretreatment temperature have significant effects on the microstructure and properties of WC-Co cermets. The prepared cermets have a mean grain size of less than 0.5 μm even with a pretreatment temperature as high as 1300°C. The WC-10wt.%Co cermet bulk prepared by the optimized milling, pretreatment, and SPS processing achieves excellent mechanical properties with a Vickers hardness of HV 1643, a fracture toughness of 13.1 MPa·m1/2 and a transverse rapture strength of 3100 MPa.

Synthesis and structural characterization of Al–B 4C nano-composite powders by mechanical alloying

This paper consists of two parts. In the first part, attrition milling of commercially available (0.7 μm) boron carbide (B 4C) particles was optimized to prepare B 4C nano-particles. In the second part of the study, mechanical alloying was successfully employed to synthesize metal matrix composite powders with a nanocrystalline Al 6061 alloy as the matrix and B 4C as the reinforcement. Different amounts of B 4C particles (5 wt.% and 10 wt.%) having various sizes of 90 nm (produced in the first part of study), 0.7 μm and 1.2 μm were mixed with different sized (21 μm and 71 μm) Al 6061 powder particles and they were milled for different times. The results showed that the nano-sized B 4C particles may be fabricated when they were milled for 110 h. The size of powder particles in the milled powder mixture was affected by the initial size and content of B 4C particles and Al powders. The SEM and TEM micrographs demonstrated a uniform distribution of B 4C particles in aluminum powders after 8 h milling of an Al + B 4C powder mixture. XRD results confirmed that the crystal size of aluminum reached to 57 nm after 16 h milling of powder mixture and addition of B 4C resulted in a finer grain size of Al in the Al + B 4C mixture during the early stages of milling.

Effect of milling energy on mechanical activation of (Mo + Si 3N 4) powders during the synthesis of Si 3N 4–MoSi 2in situ composites

Attempts have been made to study the effect of milling energy and type of grinding media on the mechanical activation during the production of MoSi 2 from a reaction between Mo and Si 3N 4. Powder mixtures of Mo and Si 3N 4 in the molar ratios of 1:1, 1:2 and 1:3 were ball milled using WC, steel, and ZrO 2 grinding media for mechanical activation. In order to evaluate the results obtained after high-energy ball milling and pyrolysis of these milled powder mixture, milling parameters have been converted to two energy parameters, namely, impact energy of the ball and total energy of milling. The optimum impact energy of ball required for mechanical activation of Mo + xSi 3N 4 ( x = 3, 2, 1) powder mixtures by WC grinding media was found to be in the range of 0.145–0.173 J, which leads to a reduction of pyrolysis temperature by 100–200 °C. Samples milled with higher impact energy than the optimum range led to formation of undesirable phases, which dilutes the effect of mechanical activation. Samples milled with both steel and ZrO 2 grinding media having lower impact energies than the optimum show the presence of enormous contamination during milling and phases like ZrSi 2, Fe 3Si and Fe 5Si 3 were observed after pyrolysis without any significant reduction in pyrolysis temperature required for MoSi 2 synthesis.