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Previous issue date: 2008-03-19 / Hard metals are the composite developed in 1923 by Karl Schr?ter, with wide application because high hardness, wear resistance and toughness. It is compound by a brittle phase WC and a ductile phase Co. Mechanical properties of hardmetals are strongly dependent on the microstructure of the WC Co, and additionally affected by the microstructure of WC powders before sintering. An important feature is that the toughness and the hardness increase simultaneously with the refining of WC. Therefore, development of nanostructured WC Co hardmetal has been extensively studied. There are many methods to manufacture WC-Co hard metals, including spraying conversion process, co-precipitation, displacement reaction process, mechanochemical synthesis and high energy ball milling. High energy ball milling is a simple and efficient way of manufacturing the fine powder with nanostructure. In this process, the continuous impacts on the powders promote pronounced changes and the brittle phase is refined until nanometric scale, bring into ductile matrix, and this ductile phase is deformed, re-welded and hardened. The goal of this work was investigate the effects of highenergy milling time in the micro structural changes in the WC-Co particulate composite, particularly in the refinement of the crystallite size and lattice strain. The starting powders were WC (average particle size D50 0.87 μm) supplied by Wolfram, Berglau-u. Hutten - GMBH and Co (average particle size D50 0.93 μm) supplied by H.C.Starck. Mixing 90% WC and 10% Co in planetary ball milling at 2, 10, 20, 50, 70, 100 and 150 hours, BPR 15:1, 400 rpm. The starting powders and the milled particulate composite samples were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to identify phases and morphology. The crystallite size and lattice strain were measured by Rietveld s method. This
procedure allowed obtaining more precise information about the influence of each one in the microstructure. The results show that high energy milling is efficient manufacturing process of WC-Co composite, and the milling time have great influence in the microstructure of the final particles, crushing and dispersing the finely WC nanometric order in the Co particles / O metal duro ? um comp?sito de matriz met?lica que tem grande aplica??o devido as suas propriedades, que aliam alta dureza e resist?ncia ao desgaste ? tenacidade. ? composto
por uma fase fr?gil, o WC, e uma fase d?ctil, que pode ser o cobalto, o ferro ou o n?quel. Destes comp?sitos, o de maior destaque ? o WC-Co, que foi desenvolvido na d?cada de 20 e
vem sendo estudado desde ent?o. As propriedades mec?nicas do comp?sito WC-Co, s?o dependentes das caracter?sticas microestruturais dos materiais de partida. Neste contexto, a
obten??o do metal duro a partir de part?culas nanom?tricas vem sendo estudada. Existem v?rios m?todos de fabrica??o de metal duro WC-Co nanoparticulado, dentre as principais
t?cnicas, a moagem de alta energia em moinho planet?rio, se mostra eficiente para este fim. Nesse processo, os p?s s?o submetidos a cont?nuos impactos, que provocam significativas
altera??es em sua microestrutura. A fase fr?gil ? refinada at? a escala nanom?trica e a fase d?ctil ? deformada e soldada, formando placas, devido o excesso de deforma??o pl?stica, as
placas tornam-se encruadas e sofrem fratura fr?gil. Simultaneamente as part?culas fr?geis s?o inseridas na fase d?ctil formando assim um comp?sito com matriz de cobalto pouco ou muito deformado e part?culas refinadas e dispersas de carbeto de tungst?nio. Estas caracter?sticas dependem das condi??es de moagem empregada. Neste trabalho foi realizada uma an?lise das caracter?sticas deste comp?sito quanto ao tamanho de cristalito, grau de encruamento, e
morfologia. O principal objetivo deste trabalho ? investigar o efeito do tempo da moagem de alta energia nas altera??es microestruturais que ocorrem no comp?sito WC-Co, no que diz
respeito ao refinamento das part?culas e a microdeforma??o da rede cristalina. Neste contexto foram utilizadas as t?cnicas de difra??o de raios X (DRX) e microscopia eletr?nica de
varredura (MEV). A t?cnica utilizada para an?lise de tamanho de cristalito e microdeforma??o da rede cristalina foi o M?todo de Rietveld. Os resultados mostram que a moagem de alta
energia foi eficiente na produ??o do comp?sito WC-Co com part?culas de WC nanom?tricas pouco ou muito encruadas
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/15529 |
| Date | 19 March 2008 |
| Creators | Pinto, Gisl?ine Bezerra |
| Contributors | CPF:80732810400, http://lattes.cnpq.br/8671649752936793, Melo, Jos? Daniel Diniz, CPF:46660640444, http://lattes.cnpq.br/6572298923055649, Gomes, Uilame Umbelino, CPF:05012180410, http://lattes.cnpq.br/9858094266525225, Lima, Severino Jackson Guedes de, CPF:09445110404, http://lattes.cnpq.br/1045652409149134, Nascimento, Rubens Maribondo do |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Engenharia Mec?nica, UFRN, BR, Tecnologia de Materiais; Projetos Mec?nicos; Termoci?ncias |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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