Abstract: Aerospace vehicle requires structures to withstand intense aerodynamic heating and propulsion system to provide very high effective heat exchange. In order to satisfy both requirements of effective thermal exchange and mechanical properties, high temperature materials, or sometimes dissimilar metals with different properties must be joined together. In this study, it is demonstrated that diffusion welding process can be applied to manufacturing lightweight integral structures of aerospace structural parts with titanium and stainless steel. The results show that the technology to design and develop the diffusion welding process of high temperature metals can be applied for manufacturing of aerospace components for high temperature application.
Abstract: The selection of optimum machining parameters plays a significant role for the quality characteristics of products and its costs for grinding. This study describes the optimization of the grinding process for an optimal parametric combination to yield a surface roughness using the Taguchi method. An orthogonal array and analysis of variance are employed to investigate the effects of cutting environment (A), depth of cut (B) and feed rate (C) on the surface roughness characteristics of mold steels. Confirmation experiments were conducted to verify the optimal testing parameters. The experimental results indicated that the surface finish decreased with cutting-fluid and depth of cut, but decreased with increasing feed rate. It is revealed that the cutting fluid environment had highest physical as well as statistical influence on the surface roughness (71.38%), followed by depth of cut (25.54%), but the least effect was exhibited by feed rate (1.62%).
Abstract: Aluminum and its alloys are widely used materials in industrial and engineering applications. They are second in use after steel due to their attractive properties e.g. strength-to-weight ratio, their electrical and thermal conductivities, and corrosion resistance. However, against these attractive properties commercially pure aluminum has certain limitations in the cast condition because it solidifies in large grain size columnar structure which reduces its mechanical strength and surface quality. It is, therefore, always alloyed with other elements to reduce or eliminate these defects. In this paper, the effect of copper addition at a rate of 4% Wt. to commercially pure aluminum both in the cast and after rolling conditions is investigated. Aluminum sheets and aluminum-4% copper sheets were cold rolled in three successive passes, from 4 mm to 3mm to 1.3 mm. After each pass, the grain size, Vickers micro-hardness and surface roughness were determined and discussed. It was found that addition of 4% Cu to commercially pure Al in the cast condition resulted in refining its microstructure both in the cast and after rolling conditions. Furthermore, the rolling process resulted in enhancement of the surface quality only after the first and second passes.
Abstract: Magnesium and its alloys are the lightest constructional available materials on earth with a maximum density of 1.78 g /cc and melting point of 650 ͦC, with good damping characteristics. Therefore; they are alloyed or micro alloyed with other elements. In this paper comparison between the addition of Ti and Ti+ B to this alloy on its grain size and its mechanical characteristics is investigated both in the cast and after direct extrusion and the obtained results are presented and discussed.
Abstract: Aluminum and its alloys are widely used materials; they are next to steel in use mainly in the automobile industry due to their high strength – to – weight ratio and corrosion resistance beside its other attractive properties. Against their attractive properties; they have the disadvantage of solidifying in columnar structure which tends to reduce their mechanical characteristics and surface quality. Therefore it became customary to grain refine them either by Ti or Ti+B to overcome this discrepancy. In this paper, comparison between Molybdenum addition to commercially pure aluminum grain refined by Ti and Ti+B on its grain size and mechanical characteristics both in the cast and after pressing by the ECAP process is investigated and the obtained results are presented and discussed.
Abstract: Impact conditions involve velocities below the sonic speed, which is normally of the order few hundreds up to few thousands m/s. The implications of impact depend on projectile and target materials, impact velocity, incident angle and the mass and shape of the projectile impacting head. The superimposition of progressing and reflected waves can lead to local stress levels that exceed the material’s strength, thus causing cracks and / or fracture at significant velocities. At low impact velocities, plastic deformation normally prevails. With increasing velocities the projectile will leave a hole in the target. With decreasing target thickness, the effects range from perforation, via internal cracks, and finally to plug formation. In this paper, the damages caused by impact which include: perforation, plugs formation and their fracture, metallurgical changes e.g. shear bands, twinning, recrystallization and phase transformation and fractures both in the projectile and the target plate are presented and discussed.
Abstract: To explore the relationship between the properties of the PTFE micropowders and the irradiation conditions, several PTFE micropowders were prepared by electron beam irradiation from 5 to 4000 kGy in air at room temperature. The properties of the irradiated PTFEs were characterized by particle size and its distribution (PSD) determination, differential scanning calorimetric (DSC) and thermogravimetric (TG) analysis, melt flow rate (MFR) and contact angle (CA) measurements. The results indicate that the particle size, the melting and crystallization temperature (Tm and Tc) and the melt viscosity of the irradiated PTFE are lower (smaller) than those of the pristine PTFE. By linear regression, the correlation between Tm (or Tc) of the PTFE micropowder and irradiation dose is established. The variation of surface properties of the irradiated PTFE micropowder is also reported.
Abstract: The aligned carbon microcoils having the straight type overall geometry could be obtained using C2H2/H2 as source gases and SF6 as an incorporated additive gas under the thermal chemical vapor deposition system. Their morphologies and crystal structures were investigated and compared with the randomly grown carbon microcoils having the coil or twist type overall geometry. We could observe the enhancement of the (002) peak in XRD spectra of the aligned carbon microcoils indicating the existence of the more regular structure in the aligned carbon microcoils. The aligned carbon microcoils were formed as a bundle shape, while the randomly grown carbon microcoils were appeared as an individual shape. The systematic growth mode for the developing aspect of the aligned carbon microcoils was proposed.
Abstract: Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Bunch-type large-sized (100 ~ 200 μm in diameter) Ni grains were used as the catalyst for the formation of the carbon coils. According to the different reaction processes, the injection time of SF6 gas flow was varied from 1.0 min to 60 min. The characteristics (formation density, morphology, and geometry) of the deposited carbon coils on the substrates were investigated according to the different reaction processes. Finally, both the high production yield of carbon coils and their geometry control could be achieved merely by manipulating SF6 gas flow injection time. Two cases growth patterns were proposed according to SF6 gas flow injection time in association with the fluorine’s characteristics for etching the materials or enhancing the nucleation sites.