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Albergaria-a-Velha, Portugal

Soares E.,University of Porto | Soares E.,Metalurgia Portuguesa do Tungstenio Lda | Malheiros L.F.,University of Porto | Sacramento J.,Metalurgia Portuguesa do Tungstenio Lda | And 3 more authors.
Journal of the American Ceramic Society | Year: 2012

Hardmetal wear tools industry has observed a consistent increase in new applications and market interest for submicrometer carbides, despite the fabrication issues related with powder processing and sintering that subsist on these new materials. New technologies with lower temperature exposure and high heating rates or optimizing the current sintering process are imperative to improve their quality and consistency. As the new sintering technologies in study are costly for industrial use and still limited in terms of flexibility, we studied and developed in this work a combined sintering approach to maximize the densification of submicrometer grades (WC 0.6 μm and WC 0.4 μm) with 3.5 and 12 wt% Co while controlling the deleterious grain growth. Sintering at solid and liquid phase was performed with vacuum sintering and post-sintering performed using Hot-Isostatic-Pressing. Thermal cycles were designed based on thermal analyses experiments performed to the powders allowing to design a densification process at lower temperatures to maximize microstructural homogeneity, densification, and reduce grain growth using current industrial technologies, reflected in high hardness and mechanical strength obtained. © 2012 The American Ceramic Society. Source


Soares E.,University of Porto | Soares E.,Metalurgia Portuguesa do Tungstenio Lda | Malheiros L.F.,University of Porto | Sacramento J.,Metalurgia Portuguesa do Tungstenio Lda | And 3 more authors.
Journal of the American Ceramic Society | Year: 2012

Submicrometer carbides (0.2-0.8 μm) are technologically important new materials because they can reach very high hardness with good mechanical resistance and excellent hardness/toughness combinations, making them especially effective for the wear tools market. Sintering of these engineering materials requires a careful process control to reach the maximum densification without damaging irreversibly the grain size, fundamental for reaching the expected properties. Especially for larger wear tools, which are more complex to produce, further know-how regarding sintering optimization is required to improve their quality and consistency. In this work, grades from WC 0.6 μm and WC 0.4 μm powders, combined with varying contents of 0.7 μm Co powder (from 2 to 12 wt%), were prepared by water technology to reach high-quality powder mixtures. Thermal analyses were performed to obtain the powders shrinkage profile and sintering temperatures. Pressed powder samples were vacuum- and sinterHIP-sintered at different temperatures on industrial furnaces and their relevant properties were analyzed. Some practical aspects, like compaction pressures, carbon content influence on sintered properties were also addressed. Low Co (<6 wt%) grades presented exceptional high hardness levels (>2200HV30) and hardness/toughness ratios (2200HV30/8.7 MPa·m 1/2) although requiring special sintering cycles at higher pressures. The data collected in this work will be further used to optimize the sintering and maximize densification of these special grades using HIP - Hot Isostatic Pressing technology. © 2011 The American Ceramic Society. Source


Soares E.,University of Porto | Soares E.,Metalurgia Portuguesa do Tungstenio Lda | Malheiros L.F.,University of Porto | Sacramento J.,Metalurgia Portuguesa do Tungstenio Lda | And 3 more authors.
Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010 | Year: 2010

The preparation of submicron and low Co hardmetal grades using water and ethanol was compared. Higher repulsive charges were found to be generated in powders surfaces when immersed in water, reducing suspensions viscosity and improving milling efficiency. Suspensions with higher solids loading and shorter milling times could then be achieved using water, without affecting microstructural homogeneity. Sintered samples with Co contents of 5.5 and 3.5 wt.% were obtained from grades prepared using both liquids. Higher quality microstructures in terms of grain size distribution, Co dispersion, porosity and fracture toughness were obtained with water milling. Significant differences found in terms of sintering behavior found can also be due to the improved Co distribution. Water processing of submicron hardmetal grades with low Co contents can bring therefore quality improvements to their production. On the other hand, water technology is also environmental friendlier, reduces investments related with equipment safety and maintenance costs, and so, figures as a promising step towards hardmetal "greener" fabrication. Source

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