Geovani Rodrigues

Evaluation of the milling efficiency increase of AISI 52100 steel using niobium carbide addition through high energy ball milling

The AISI 52100 is a tool-type steel and is more often used in industry for the production of bearings. After the end of its life cycle, it is discarded or remelted, but both processes are considered expensive. Thus, the possibility of reusing this material through the powder metallurgy (PM) route is considered advantageous, since it transforms a waste into another product. To obtain the starting powders, the AISI 52100 steel scrap was submitted to a process of high energy ball milling, which was milled pure and with 1 and 3 % of niobium carbide (NbC) additions. Those additions were performed with the intention of increasing the milling efficiency of the steel, through formation of a metal-ceramic composite with a ductile-fragile behaviour. To determine the morphology and particle size, scanning electron microscopy (SEM) and particle size distribution tests were used. The results indicated that with the carbide addition, a significant increase in the milling efficiency was achieved, being possible to obtain nanoparticles after 20 hours of milling time.

Magnetic and Electrical Properties of MnxCu1-xFe2O4 Ferrite

In the present work, mixed manganese-copper ferrite of composition MnxCu1-xFe2O4 (within x=0.40, 0.42, 0.44, 0.46, 0.48 and 0.50) have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization. MnxCu1-xFe2O4 ferrite samples were prepared by uniaxial pressing from the oxide mixture, synthesized at 1000°C during 45 hours and finally heated to 1200°C by 5h, at room atmosphere. The X-ray diffractograms show that the samples with different compositions were formed by compact structure spinel with cubic cell. The saturated magnetization of the MnxCu1-xFe2O4 ferrites increased with x up to 0.46, which presented the smallest coercitive field. All samples showed hysteresis characteristic of soft magnetic materials. This electrical behavior is compatible with an insulator. The results were analyzed in the framework of grain/barrier model.

Isothermal section of the Ti-Si-B system at 1250 ° C in the Ti-TiSi2-TiB2 region

region) of the ternary Ti-Si-B system at 1250 °C was determined from heat-treated alloys prepared via arc melting. Microstructural characterization has been carried out through scanning electron microscopy (SEM), X-ray diffraction (XRD) and wavelength dispersive spectrometry (WDS). The results have shown the stability of the near stoichiometric Ti

Assessment of serotonergic system in formation of memory and learning

We evaluated the involvement of the serotonergic system on memory formation and learning processes in healthy adults Wistar rats. Fifty-seven rats of 5 groups had one serotonergic nuclei damaged by an electric current. Electrolytic lesion was carried out using a continuous current of 2mA during two seconds by stereotactic surgery. Animals were submitted to learning and memory tests. Rats presented different responses in the memory tests depending on the serotonergic nucleus involved. Both explicit and implicit memory may be affected after lesion although some groups showed significant difference and others did not. A damage in the serotonergic nucleus was able to cause impairment in the memory of Wistar. The formation of implicit and explicit memory is impaired after injury in some serotonergic nuclei.

Drawing Tantalum Encapsulated in the Cooper Pipe

Tantalum has characteristics such as excellent ductility, high corrosion resistance, high mechanical strength at high temperatures and high resistance to etching of acids and bases. Its high ductility allows the realization of large reductions without the need for intermediate heat treatment. A process for the production of tantalum wire is drawing. However, when using this process, the high ductility of the tantalum (Ta) metal causes a retention/accumulation of the Ta in the spinneret. Therefore, to be drawn is necessary that the tantalum is encapsulated in a copper tube. In this work was produced a Ta wire by means of rotary forging and drawing process. In the drawing process of the tantalum encapsulated in copper tube, was the appearance of striation on the surface of tantalum, when applied to an area reduction (AR) of approximately 22%. This fact is possibly related to the different sliding systems with consequent formation of non-hydrostatic stress fields at the interface Cu / Ta. After an area reduction (AR) of 94% the Cu was removed from the surface of the wire, through chemical etching, and this wire was drawn up to 0.43mm without retention/accumulation of the Ta in the spinneret.

The Influence of Different Microstructures to Fracture Toughness and Hardness of Quenched LNE 380 Steel at Different Temperatures

In this work it was analyzed the evolution of mechanical properties of Dual-Phase steel as a function of volume fractions of ferrite and martensite, obtained from steel type LNE 380. The intercritical region and the existing phases in function of temperature were determined using the THERMOCALC software. The samples of steel were quenched at different temperatures to obtain differents microstructures consisting of ferrite, pearlite and martensite. The microstructural characterization of the samples was performed by qualitative and quantitative metallography. The mechanical properties were determined by hardness and impact tests. It was concluded that the volume fraction of ferrite and martensite calculated experimentally agrees with the simulation and the variation of these fractions affects significantly the hardness of the steel, but does not significantly affect the results of fracture toughness.