Papers by Author: José Hélio Duvaizem

Abstract: Ti-13Nb-13Zr alloy produced via powder metallurgy was submitted to heat treatment under various conditions and the effects on microstructure and elastic modulus were investigated. Heat treatment was performed using temperatures above and below α/β transus combined with different cooling rates – furnace cooling and water quenching. Microstructure and phases were analyzed employing scanning electron microscopy and X-ray diffraction. Elastic Modulus was determined using a dynamic mechanical analyzer (DMA). The results indicated that α phase precipitation and elastic modulus values increased after heat treatment performed using temperature below α/β transus. However, when it was performed above α/β transus and using higher cooling rate, a decrease in elastic modulus was observed despite higher α phase precipitation, indicating that the microstructural modifications observed via SEM, due to the presence of martensitic α phase, influenced on elastic modulus values.

Abstract: In this present work Ti-13Nb-13Zr alloy was produced by PM using planetary ball mill with zirconium oxide grinding bowl and balls to reduce contamination. The effect of milling time upon microstructure and microhardness was studied. Powders have been produced by hydrogenation of Ti, Nb and Zr at 1MPa. Milling speed was 200 rpm during 90 to 360 min. Sintering was carried out at 1150°C during 10h. Powder size distribution was analyzed using CILAS equipment and chemically characterized by X-Ray Fluorescence (XRF). Microhardness was determined by means of a Vickers microhardness tester. Microstructure and phases were analyzed employing scanning electron microscopy (SEM) and X-Ray diffraction.

Abstract: The first goal of this work involved the study of HDDR powders obtained from annealed alloys with the general formula: PrxFe77.9-xCo16B6Nb0.1 (x = 12; 12.5; 13; 13.5 and 14). The alloys were processed at desorption / recombination temperature of 840°C. The highest magnetic properties were obtained with 13.5 at. % Pr (Br= 1000mT and µ0iHc= 890mT). The alloy with a minimum praseodymium content (12 at. %) exhibited the lowest magnetic properties (Br= 350mT e iHc= 120mT). The second aim of the work involved the characterization of HDDR powders using X-ray diffraction for phase quantification and mean crystallite sizes determination of the hard magnetic phase. The processed powders were characterized by scanning electron microscopy (SEM).

Abstract: The effects of the hydrogenation stage on microstructure and mechanical properties of Ti-13Nb-13Zr alloy produced by powder metallurgy have been studied. Powder alloys have been produced by hydrogenation with 250 MPa or 1 GPa and via high energy planetary ball milling. Samples were isostatically pressed at 200 MPa and sintered at 1150 °C for 7, 10 and 13 hours. Elastic modulus and microhardness were determined using a dynamic mechanical analyzer (DMA) and a Vickers microhardness tester. Density of the samples was measured using a liquid displacement system. Microstructure and phases presents were analyzed employing scanning electron microscopy (SEM). Elastic modulus was 81.3  0.8 and 62.6  0.6 GPa for samples produced by 250 MPa and 1 GPa hydrogenation, respectively when sintered for 7h.

Abstract: Fine magnetic powder has been produced using the hydrogenation disproportionation desorption and recombination (HDDR) process. The first goal of this work involved an investigation of a range of disproportionation/desorption temperatures between 800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy. The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum disproportionation temperature for achieving high anisotropy was 820°C. The influence of the reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR powders and magnets has been shown. A second stage of this study involved the characterization, for each temperature, of the HDDR processed powder using X-ray diffraction analysis. Samples of the HDDR material have been studied by synchrotron radiation powder diffraction using the Rietveld method for cell refinement, phase quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has also been employed to reveal the morphology of the HDDR powder.