WC-(Cu, Fe, Cr, Ni) composites attained by mechanosynthesis

• Autor(a) principal: Puga, Joel Bento
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/12263
• topic: Engenharia de materiais - Teses de mestrado; Carboneto de tungsténio; Materiais metálicos - Propriedades mecânicas; Sinterização

This work aims to study the feasibility of replacing cobalt by copper and stainless steel in tungsten carbide composite. The composites were prepared with a binder content of 12 wt% using the powder metallurgy method in which the conventional milling was replaced by high energy ball milling. To obtain a composite with high density, good microstructure uniformity and controlled phase composition, suitable for a good mechanical performance, the processing conditions of the high energy ball milling (HEBM) and sintering methods were enhanced. Within the studied parameters, the prime milling conditions were found at the rotation speed of 350 rpm and ball-to-powder weight ratio of 20:1, varying the milling times between 8-10 hours for the studied compositions. The HEBM process was able to reduce the particle size of the composite powders down to the nanoscale and a good binder homogenization was reached. After compacting, the powders were submitted to vacuum sintering, in a temperature range of 1300 – 1500ºC followed by HIP (hot isotactic pressing). This procedure allowed attaining dense compacts and introduce efficiently copper in the stainless steel binder up to 30%, without substantial decrease of the sintered relative density. The WC-SS composite powders show a significant amount of M6C phase formed during sintering, endorsed by the high reactivity of the small powder particles and the appearing of the M6C phase. Adding copper to the WC-SS composite allowed the decrease of the M6C phase formation. The WC-Cu sintered samples revealed two distinct major phases, W2C and Cu0.4W0.6 and their appearance depends on the applied sintering technique, in the case of being conventional or two stages sintering, respectively. The mechanical characterization revealed that the hardness of the WC-SS compacts is equivalent to the reported values in the literature for WC-Co. On the other hand, the fracture toughness remains below the reference values. Nevertheless, it was possible to attain a good balance between hardness and fracture toughness in the WC-(SSCu) composites, which make them promising candidates for substituting the traditional WC-Co composite.