Papers by Author: L.C.E. da Silva

Abstract: The aim of this work, using the powder metallurgy process, is to synthesize metallic alloys with high mechanical strength and high electric conductivity, after melting optimizing and thermal treatments. The Cu-Ni-Cr (wt%) alloys are characterized in their mechanical and electrical properties as well as the obtained microstructure. Through the process of powder metallurgy, contacts and structural parts can be obtained. The alloys elements are added to copper with the intention to improve their strength, ductility and thermal stability, without causing considerable damages in their form, electrical and thermal conductivity, and corrosion resistance. The metallic powders were mixed for a suitable time and then they were pressed in a cold uniaxial pressing (1000 kPa). Afterwards, the specimens were sintered in temperatures varying from 700 up to 800oC under vacuum. At last, the samples were homogenized at 550oC under vacuum, for special times. The comparative analysis is based on the sintered density, densification parameter, hardness, macrostructures and microstructures of the samples. The alloys were characterized by optical microscopy, x rays powder diffraction, electrical conductivity and Vickers hardness.

Abstract: The aim of this article was to analyze the microstructural development in samples of Cu-Ni-Sn alloys (weight %) obtained by powder metallurgy (P/M). The powders were mixed for 1/2 hour. After this, they were pressed, in a cold uniaxial pressing (1000 kPa). In the next step the specimens were sintered at temperatures varying from 650 up to 780°C under vacuum. Secondly, the samples were homogenized at 500oC for several special times. The alloys were characterized by optical microscopy, electrical conductivity and Vickers hardness. X rays powder diffraction data were collected for the sintered samples in order to a structural and microstructural analysis. The comparative analysis is based on the sintered density, densification parameter, hardness, macrostructures and microstructures of the samples.

Abstract: In this work a 50Ni50Ti at % powder mixture, commercially pure, prepared by mechanical alloying in an attritor with the following conditions: the milling speed and the ball charge were 1500 rpm and 15:1 respectively. The milling time was 1h under a nitrogen atmosphere at room temperature. After milling it was determined the particles size distribution, the phases by Xray diffractions (XRD) and the powder morphology by scanning electron microscopy (SEM). The powders after milling were compacted and hot extruded at 600 °C with an extrusion ratio of 3 to 1 and characterized by evaluation the density and microstructural determination by optical microscopy. The obtained results are discussed to show that this route could be an alternative route to prepare the shape memory alloy.