Thermal Stability and Mechanical Properties of Al-Al2O3 Nanocomposite Produced by Mechanical Milling and Hot-Pressing

In this study, Al-Al2O3 nanocomposite powders containing 5, 10 and 15 Wt% of nanopowder were produced by mechanical alloying. For comparing, Al-Al2O3 composite powder containing 5Wt% of micrometric Al2O3 was also produced. The powder was then hot-pressed in a mold to produce bulked parts. The effect of Al2O3 content on grain growth, density, hardness and bending strength of bulked composite was discussed and microstructures were investigated by optical, scanning and transmission electron microscopy. The results revealed that when nanometric particles were used instead of micrometric particles the grain growth was reduced, while the increase of particle weight percentage did not affect the grain growth. The results also showed that when weight percentage of nanometric particles was increased, although hardness of bulked parts was increased but relative density and bending strength was reduced severely. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3493

Structural Evolutions of Nanostructured CoAl Intermetallic Compound during Mechanical Alloying and Subsequent Heat Treatment

Nanostructured B2-CoAl has been successfully synthesized directly by MA of nominal composition of Co50Al50. The CoAl phase was found to be formed in an ordered structure via a gradual reaction which completed in less than 10 h. However, further milling up to 45 h led to disordering of the CoAl with a relatively constant long-range order parameter of 0.82. Lattice parameter measurements showed that disordering of CoAl was caused by triple defect mechanism. The results of isothermal annealing showed that the grains grew after isothermal annealing up to 0.7 Tm but still remained below 100 nm. The grain growth behavior was well described by the parabolic kinetics equation. The grain growth exponent remained constant above 873 K offering that grain growth mechanism does not change at high temperatures. The grain growth exponents and activation energies offered the mechanism of diffusing Co and Al atoms in the two separate sublattices at high temperatures. The equation 4 4 13 D D0 6 10 exp 175 RT t was suggested to describe the grain-growth kinetics of nano-crystalline CoAl during isothermal annealing at temperatures above 0.5Tm (873 K). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3511

Friction-stir welding of ultrafine grained austenitic 304L stainless steel produced by martensitic thermomechanical processing

An ultrafine grained 304L austenitic stainless steel was produced by martensitic thermomechanical processing and joined by applying Friction Stir Welding (FSW). The thermomechanical processing comprised a cold roll procedure up to 80% reduction followed by annealing. After FSW, different grain structures in different regions of the weld nugget were observed due to the asymmetry in the heat generation during the welding process. Grain growth was found to be the most predominant phenomena in the region just ahead of the rotating tool during the thermal cycle of FSW. A banded structure was observed in the advancing side of the weld nugget. TEM observations revealed that nanometric sigma phase precipitates were present both in the grain boundaries and inside the grains of this region. Shear textures were clearly identified in the weld center. The lack of rotated cube texture shows that the discontinuous dynamic recrystallization (DDRX) is not active in the final microstructure. Increasing the welding speed can reduce the final grain size of the weld nugget leading to higher hardness. Hardness is found to increase in the weld and this is not just a grain refinement effect, but also due to the presence of sub-boundaries and a high density of dislocations.postprin

Formation of Nanostructured Al-Mg-Si Alloys and Evaluation Its Properties

In this study, nanostructured Al-Mg-Si (Al6061) alloy was prepared from elemental powders by mechanical alloying and heat treatment. 98.4% aluminum, 1% magnesium, 0.6% silicon powders were mixed and mechanically alloyed under argon atmosphere. The rotation speed of 500rpm and ball to powder ratio of 10:1 was employed. The mechanical alloyed powder was isothermally heat treated at 400 degrees Celsius for 2 h under argon atmosphere. The results showed that after 10h of milling, a solid solution of Al-Mg-Si with a grain size of ~ 40 nm was produced. The as milled and annealed powder was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness values of alloy increase by increasing MA time. Mg2Si particles precipitate from solid solution during subsequent annealing. The as milled powder appeared to have good thermal stability against grain growth so that the grain size after annealing remained constant (~ 40 nm). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3486

The role of martensitic transformation on bimodal grain structure in ultrafine grained AISI 304L stainless steel

In the present study, metastable AISI 304L austenitic stainless steel samples were subjected to different cold rolling reductions from 70% to 93%, followed by annealing at 700 °C for 300 min to form ultrafine grained (UFG) austenite with different grain structures. Transmission electron microscopy (TEM) and nanoindentation were used to characterize the martensitic transformation, in order to relate it to the bimodal distribution of the austenite grain size after subsequent annealing. The results showed that the martensite morphology changed from lath type in the 60% rolled sample to a mixture of lath and dislocation-cell types in the higher rolling reductions. Calculation of the Gibbs free energy change during the reversion treatment showed that the reversion mechanism is shear controlled at the annealing temperature and so the morphology of the reverted austenite is completely dependent on the morphology of the deformation induced martensite. It was found that the austenite had a bimodal grain size distribution in the 80% rolled and annealed state and this is related to the existence of different types of martensite. Increasing the rolling reduction to 93% followed by annealing caused changing of the grain structure to a monomodal like structure, which was mostly covered with small grains of around 300 nm. The existence of bimodal austenite grain size in the 80% rolled and annealed 304L stainless steel led to the improvement of ductility while maintaining a high tensile strength in comparison with the 93% rolled and annealed sample.postprin

Development and Characterization of Nanostructured Ti6Al4V Alloy

Nanostructured Ti6Al4V alloy was successfully formed through mechanical alloying of a stoichiometric mixture of Ti, Al and V powders. Phase evolutions of the milled powders were investigated by XRD. The Ti(Al,V) solid solution formed after 10 h milling. Prolongation of the milling process up to 20 h lead to a structure consisting of the B-Ti phase in the a-Ti(Al) matrix. The nanostructured Ti6Al4V alloy had a grain size and hardness of 20 nm and 600 Hv respectively. Thermal stability of the alloyed powder was good as it's hardness increased to 950 Hv after 5 hr heat treatment at 1100 degrees Celsius. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3488

Intractable Seizure Disorders: Efficacy of The Classic Ketogenic Diet

 ObjectiveThe ketogenic diet is a high-fat, low carbohydrate, adequate protein diet,developed in the 1920s for the management of intractable seizure disorders in children. To evaluate efficacy and tolerability of the classic  ketogenic diet, we analyzed records of the children started on the diet from 1999 to 2006 at the Mofid children's hospital.Materials & Methods The subjects were 87 children, mean age 55 months. Before initiation of the diet, 55% of the patients had seizures, at least 1-4 times per day, 36% - 5 or more per day and 9% - 2 to 4 times per week. Mean number of Anti Epileptic Drugs (AEDs) tried for them was 8 and 67% were receiving three or more drugs.Results The ketogenic diet showed drastic improvement, with at least 50% reduction in seizure frequency in 87% of our patients, 39% of whom showed complete seizure control in the third month. After one year, in 80% of the patients who returned, improvement  continued, with 26% of them being seizure free; besides, 23% had one AED decreased, 36% had two or three AEDs decreased, and 25% (one child) had all AEDs discontinued. Of the 30 improved cases, 20%, at the end of the first year, had improved behavior as  well, and 23% of them had become more alert. The median diet duration of the improved group was 15 months.Conclusion The improvement in our patients, low  side effects, and the duration of diet by families reveal that the ketogenic diet can still be a very useful alternative therapy in certain epileptic children.