Papers by Author: S.F. Moustafa

Abstract: Elemental powders of tungsten, nickel, iron and cobalt of compositions corresponding to (W-3.2Ni-0.8%Fe), (W-3.5Ni-1.5%Fe), and (W-4.5Ni-1.0Fe-1.5%Co) were mechanically alloyed in a tumbler rod mill for 2 hrs. Mechanically alloyed powders were liquid phase sintered at 1500oC for 90 min in vacuum. The sintered materials were heated up to 1150-1200oC in vacuum atmosphere, followed by quenching in water to suppress the impurity segregated at grain boundary. The sintered materials were subjected to cold-working by swaging from 8-30% reduction in area. The swaged specimens were age-hardened at 700oC. Full characterization for both the elemental powders and the sintered tungsten alloys were performed using optical microscopy, SEM analysis, EDS quantitative analysis, X-ray diffraction, hardness and compression testing. This paper will discuss the effects of the elemental powders characterization and the liquid phase sintering parameters on the microstructure and strength of these three tungsten heavy alloys.

Abstract: Nanostructure composites of Copper-Alumina were successfully produced by new mechanochemical method using two different routes. First, route A was carried out by addition of coarse copper to aqueous solution of aluminum nitrate, and second, route B was also carried out by addition of coarse copper to aqueous solution of aluminum nitrate and ammonium hydroxide. In both routes, the mixtures were heated in air and milled mechanically to get the oxides powders of CuO and Al2O3. The CuO was reduced in preferential hydrogen atmosphere into fine copper. The composite powders have been cold pressed into briquettes and sintered in hydrogen atmosphere. The structure and characteristics of powders as well as sintered composites produced from both routes were examined by XRD, SEM, EDS, TEM and metallographic techniques. The results showed that, in both routes, nano-sized particles of alumina were formed and dispersed within the copper matrix. The structure revealed the formation of CuAlO2 spinel structure at copper alumina interface. Nanocomposites produced by route-B showed finer alumina particles of 30 nm compared to 50 nm produced by route-A resulting in improved properties in terms of relative density, macro and microhardness values.

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.