Papers by Author: W.M. Daoush

Abstract: Mechanical alloying (MA) is a solid-state powder processing method which has the ability to synthesize a variety of new alloy phases including supersaturated solid solutions, nanocrystalline structures, amorphous phases and intermetallic compounds. In this investigation, the interaction between aluminum and iron caused by MA of Fe-xAl (where X ranged from 30 to 90%) was studied as a function of milling time and post heat-treating temperatures. The sequences of structural and/or phase transformation and the behavior of mechanically alloyed powders have been assessed using XRD, hardness and magnetometer. It was found that during mechanical milling of elemental powder Al and Fe, five milling stages were categorized, namely, particle flattening, welding predominance, equiaxed formation, random welding orientation and steady state composite particles. All milled powders showed nano-sized powder mixtures after milling for 20hrs. When Fe-30%Al powder was milled for 150hrs, a partially ordered AlFe phase was obtained. However, when these saturated solid solutions were heat treated at 500 °C, the AlFe intermetallic was precipitated fully ordered. When the Al content was increased up to 40% and milled for 50hr, the XRD pattern showed a broad halo spectrum which showed the formation of an amorphous phase. When a Fe-60%Al powder mixture was mechanically milled for 50hr, the Al5Fe2 intermetallic formed that was associated with an amorphous phase, which transformed into the Al3Fe intermetallic by heat treating at 500°C. In the case of Fe-75% and Fe-90%Al milled for 150hrs only Al peaks appeared and were shifted to higher angles, suggesting that Fe atoms diffused into Al, leading to the formation of a solid solution.

Abstract: A nanosized cobalt-based alloy containing 20 wt % Fe was synthesis by electroless chemical reduction method using alkaline tartarate bath and sodium hypophosphite as a reducing agent . The powder was investigated by optical microscope, SEM and XRD to identify the powder shape, size and the chemical composition. The prepared powder has a spherical shape with a particle size of about 200 nm. The investigated powder was cold compacted at 600 MPa and then sintered in hydrogen atmosphere at 1050 0C. Metallographic, physical, magnetic and electrical properties investigations were carried out for the prepared powder and its sintered compacts. The prepared powder has 2.5% phosphorus content which was liberated by heating the compacts to the sintering temperature in hydrogen atmosphere. From the results of the density measurements we can observe that the prepared sintered FeCo material had a relative density about 96% to the theoretical. But the results of the electrical properties measurements give an indication of the decreasing in the electrical resistivity than the materials produced by the traditional methods. On the other hand the magnetic measurements, of the FeCo powder has a lower specific saturation induction, Bs, than the sintered one which was due to the presence of the paramagnetic metal phosphides in the powder but after rising the temperature to sintering the, Bs, values is increased due to the conversion of the phosphides to the metallic state and the phosphorus was liberated, but the coercive force was decreased by sintering of the powder compacts by lowering the porosity of the materials with sintering and the formation of the soft magnetic materials Fe-Co solid solution which was investigated by XRD having the highest specific saturation induction value. Also the magnetic permeability of the prepared sintered material was increase with increasing the applied field until 50 Oe which has the highest value and decreased with increasing the field more than 50Oe. From the magneto-resistance measurements, it was shown that the sintered material has a positive magneto-resistance in the field direction but a negative one in the direction perpendicular to the current and the field.

Abstract: Nano sized Co-20wt%Ni composite powder was synthesized by electroless chemical reduction method using metallic salt precursors and hypophosphite as a reducing agent in alkaline tartarate bath as a complexing agent. The synthesized powder provide better sinterability, mechanical, electrical and magnetic properties with homogeneous microstructure. The nano-sized powder could be obtained, which have the average particle size of 40 nm, with a saturation magnetization (Bs ) of 97.95 which was increased by heat treatments of powder in hydrogen to 127 emu/g due to the exclusion of the precipitated phosphrous in the composite powder. The powder underwent cold compaction at 600 Mpa and sintering at 1050 oC for 30 min. The saturation induction for the sintered material of 149.3 emu/g higher than the synthesized powder and has electrical resistivity value of 7.6 μcm.