Estudo da obtenção de um compósito W-20%Ag a partir da decomposição e redução de pós de paratungstato de amônio e nitrato de prata preparados por moagem de alta energia e sinterizados em forno resistivo
The union of a refractory metal such as tungsten (W) and an internal transition metal such as silver (Ag) allows the formation of a composite with excellent quality for applications in electrical contacts, heat sinks and microwave absorbers. The W-Ag composite combines the high melting point (3,410...
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| Formato: | bachelorThesis |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/42925 |
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| Resumo: | The union of a refractory metal such as tungsten (W) and an internal transition metal such as silver (Ag) allows the formation of a composite with excellent quality for applications in electrical contacts, heat sinks and microwave absorbers. The W-Ag composite combines the high melting point (3,410 ° C) and the high wear resistance of the hard tungsten phase with the high thermal, electrical conductivity and good workability of the silver ductile phase. Obtaining this type of material through the powder metallurgy route, through the mixing of powders, compaction and sintering enables the production of more complex geometries and with any composition. However, the mutual insolubility of both components makes it impossible to obtain sintered composites with a density close to or equal to theoretical. This work investigates the influence of the sintering temperature in the compacts of composite powders W-20%Ag obtained from the reduction of powders of ammonium paratungstate and silver nitrate in the proportion of APT-21,71%AgNO3 prepared by high energy ball milling. The effect of the reduction and decomposition process to obtain W-20%Ag was investigated through the densification, microstructure and properties of sintered compacts. The precursors of ammonium paratungstate with 21,71% of silver nitrate, were ground in a high-energy Pulverisset 6 planetary mill with container and carbide balls. The mass ratio of powder to balls used was 1: 5 and the milling was carried out in an atmosphere of ethyl alcohol, at 400 rpm for 40 h. a W-20% Ag powder was also obtained by mechanical mixing to serve as a reference. Compacts of composite powders W-20% Ag obtained from APT-21,71%AgNO3 powders prepared by mechanical mixing and ground for 40 h were reduced to 800 ° C for 1 h in a tubular oven under a flow of H2 of 316 ml / min. Such compacts were pressed at 200 Mpa in a uniaxial cylindrical matrix and sintered at 900 ° C and 1000 ° C for 1 h under H2 atmosphere. The compacted sintered at 900 ° C reached a relative density reaching 61%, while those sintered at 1000 ° C reached 73% relative density. The sintering temperature is also effective for increasing hardness, however, values can change according to a phase identified in the microstructure, reaching a maximum of 974 HV on average for the 40h HEM process and sintering at 1000 ° C. |
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