Preparation And Characterization Of UItrafine Co And Co-Cr-V Alloy Powders

Co powder is widely used in carbide as binder. Usually it is s very difficult to grow a crystal grain size of less than200nm in the preparation of WC-Co cemented carbide by added gain inhibitors typically in industry. By changing the way adding grain growth inhibitors, V and Cr solid solution phase in Co To prepare with the "double high"(high strength, high hardness) carbide. This paper attempt to preparation ultrafine Co powder by chemical reduction and Co-Cr-V composite powders were prepared by oxalate coprecipitate process.1) Preparation of ultrafine Co powder by chemical reductionThe first part of this paper investigate preparation of ultrafine cobalt powder by chemical reduction method, hydrazine hydrate and sodium hypophosphite was used as reducer, cobalt chloride was used as raw materials. The influence of the content of hydrazine and sodium hypophosphite on the microstructure, morphology, and grain size of ultrafine cobalt was characterized by scanning electron microscope and X-ray diffraction. The results showed that:the morphology of cobalt powder varies with the content of hydrazine hydrate, with the increasing content of hydrazine hydrate, the morphology of cobalt shifted from spherality to dendritic. When the concentration of hydrazine hydrate is4mol, the morphology of cobalt powder was presented as spherical-like or rod-like, while the morphology tend to presented as snow-like for6mol (or8mol) and dendrimer-like for10mol. Cobalt powder increase over the reaction time, and the reaction come to an end after about15min. the purity of cobalt is the highest when the pH was maintained at10.5-11, which reached92%.2) Preparation of Co-Cr-V composite powders by oxalate coprecipitate processThe second half of this paper studied Co-Cr-V composite powders were prepared by oxalate coprecipitate process. Co-Cr-V composite powders were prepared by calcination-hydrogen reduction orthermal decomposition in a vacuum of precursor which was synthetised by oxalate coprecipitate process. Changing the pH, reaction temperature and Calcination atmosphere of coprecipitation respectively. Calcination temperature was analyzed by differential scanning calorimetry (DSC). And the phase analysis and the micro-structure of the samples was characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Discussing the effect of pH, reaction temperature and Calcination atmosphere on the phase, morphology and grain size of the metal composite power. The results show that:V and Cr can be very good solid solution in Co phase by oxalate co-precipitation method.There have a great influence on the preparation of Co-Cr-V composite powder by Changing in pH, reaction temperature, Calcination atmosphere and other process. The particle size distribution of metal powders in acid is more uniform than that in alkaline. Bet analysis showed that the specific surface area of the powder calcined under argon atmosphere was the biggest, and the particle size was the smallest.32figuers,12tables,72referemces.