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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Efeito da moagem de alta energia na microestrutura e nas propriedades magn?ticas do comp?sito wc-10%p.Co

Manuel, Jo?o Baptista 19 May 2008 (has links)
Made available in DSpace on 2014-12-17T14:06:58Z (GMT). No. of bitstreams: 1 JoaoBM.pdf: 4159366 bytes, checksum: 0675996da75ecb96ee8b23855ac7f866 (MD5) Previous issue date: 2008-05-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work a studied the high energy milling effect in microstructure and magnetic properties of the WC-10wt.%Co composite. The composite powders were prepared by mechanical mixed and milled at 2 hours, 100 hours, 200 hours and 300 hours in planetary milling. After this process the composite were compacted in stainless steel die with cylindrical county of 10 mm of diameter, at pressure 200 Mpa and sintered in a resistive furnace in argon atmosphere at 1400 oC for 5 min. The sintered composite were cutted, inlaid, sandpapered, and polished. The microestrutural parameters of the composite was analyzed by X-ray diffraction, scanning electronic microscopy, optical microscopy, hardness, magnetic propriety and Rietveld method analyze. The results shows, with milling time increase the particle size decrease, it possibility minor temperature of sintering. The increase of milling time caused allotropic transformation in cobalt phase and cold welding between particles. The cold welding caused the formation of the particle composite. The X-ray diffraction pattern of composite powders shows the WC peaks intensity decrease with the milling time increase. The X-ray diffraction pattern of the composite sintered samples shows the other phases. The magnetic measurements detected a significant increase in the coercitive field and a decrease in the saturation magnetization with milling time increase. The increase coercitive field it was also verified with decrease grain size with milling time increase. For the composite powders the increase coercitive field it was verified with particle size reduction and saturation magnetization variation is relate with the variation of free cobalt. The Rietveld method analyze shows at milling time increase the mean crystalline size of WC, and Co-cfc phases in composite sintered sample are higher than in composite powders. The mean crystallite size of Co-hc phase in composite powders is higher than in composite sintered sample. The mean lattice strains of WC, Co-hc and Co-cfc phases in composite powders are higher than in composite sintered samples. The cells parameters of the composite powder decrease at milling time increase this effect came from the particle size reduction at milling time increase. In sintered composite the cells parameters is constant with milling time increase / O presente trabalho estudou o efeito da moagem de alta energia nos par?metros microestruturais e nas propriedades magn?ticas do comp?sito WC-10%pCo. Os p?s comp?sitos foram processados em moinho planet?rio por mistura mec?nica e mo?dos por 2 h, 100 h, 200 h e 300 h. Os comp?sitos em p? foram compactados numa matriz de 10 mm de di?metro a uma press?o de 200 Mpa e sinterizadas a 1400 0C/ 5 min no forno acoplado ao dilat?metro com atmosfera de arg?nio. Os comp?sitos foram submetidos a um processamento metalogr?fico de corte, embutimento, lixamento e polimento. A caracteriza??o dos comp?sitos consistiu em difra??o de raios-X, microscopia ?ptica, microscopia eletr?nica de varredura, dureza, propriedades magn?ticas e an?lise dos par?metros microestruturais pelo m?todo de Rietveld. Os resultados mostram que o tempo de moagem promove uma redu??o do tamanho de part?cula. Os comp?sitos com maior tempo de moagem sinterizam a menor temperatura. O tempo de moagem promove ainda a soldagem a frio das part?culas originando a forma??o de part?culas comp?sitas e transforma??es alotr?picas na fase cobalto. O difratograma de raios-X para os p?s comp?sitos mostra uma queda da intensidade dos picos de WC com o tempo de moagem. O difratograma de raios-X para os comp?sitos sinterizados mostra a presen?a de outras fases. As medidas magn?ticas detectaram um decr?scimo na magnetiza??o de satura??o e um crescimento no campo coercitivo com o aumento do tempo de moagem. Com o tempo de moagem foi verificado um decr?scimo do tamanho de gr?o. Para os p?s comp?sitos o aumento do campo coercitivo est? relacionado com a redu??o do tamanho de part?cula e a varia??o da magnetiza??o de satura??o est? relacionada com a varia??o do cobalto livre. O m?todo de Rietveld mostrou que a varia??o do tamanho m?dio do cristalito com o tempo de moagem das fases WC e Co-cfc foi menor nos comp?sitos sinterizados do que nos p?s comp?sitos. J? na fase Co-cfc esta varia??o foi maior nos p?s. A deforma??o m?dia do cristalito das fases WC, Co-hc e Co-cfc ? maior nos p?s comp?sitos do que nos comp?sitos sinterizados. Nos p?s comp?sitos os par?metros de rede para as fases WC, Co-hc e Co-cfc decrescem com o tempo de moagem. Este decr?scimo est? diretamente influenciado pela redu??o do tamanho das part?culas. Para os comp?sitos sinterizados os par?metros de rede para as fases WC, Co-hc e Co-cfc s?o praticamente constantes

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