Estudo da microestrutura e das propriedades do metal duro WC- (Fe-Nb/NbH-C) obtido por moagem de alta energia e spark plasma sintering

Abstract

The search for alternative binders for hardmetals, also called cemented carbides, has moved the scientific community. Alternative Fe-based binders have been widely studied and used in selected applications. An unprecedented addition to this ligand would be the use of niobium, a metal of high global interest, few explored and abundant in Brazilian territory. This work aims to investigate the properties of the Fe-Nb/NbH-C system, using it as an alternative binder to produce WC-(Fe-Nb/NbH-C) cemented carbides. For this purpose, high energy ring and planetary milling techniques were used, using controlled atmosphere sintering and spark plasma sintering (SPS) techniques in a sintering temperature range from 1150ºC to 1450ºC. To evaluate the composition, microstructure and properties, the ThermoCalc software was used, in addition to the XRD, MO, SEM, WDS, density, Vickers hardness and fracture toughness techniques. The preliminary results pointed to planetary mill as the most efficient method for homogenization and particle size reduction, resulting in samples with better mechanical properties. Controlled atmosphere sintering for this application proved to be unfeasible, on the other hand, spark plasma sintering proved to be an efficient method for the production of densified samples. The sintering temperature of 1250ºC provided the best microstructure and properties results for all SPS processing conditions. Replacing Nb for NbH, it was possible to obtain samples with more homogeneous and densified microstructure by reducing the size of the niobium particles, absence of eta phase, and a remarkable microstructural gradient formation, as well as hardness values of up to 1620Hv, meaning an increase of approximately 15% in relation to pure niobium compositions.