چكيده به لاتين
In the present study, mechanical alloying process was used to produce Co-Cr alloy due to its unique properties and high melting point of Co-based alloys. In this investigation, the experiments were done in 4 general sections that at all of them, the milling process was carried out by a high energy ball mill with the ratio of ball to powder of 15:1 and with the speed of 400 rpm at room temperature and atmosphere. Then the products of mechanical activation were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). At first stage, mechanochemical activation of cobalt oxide with graphite was studied. Results of XRD showed that within 72 hours of activation, reduction reaction did not occurred. Because of, not reducing cobalt oxide at the second stage, different Al stoichiometric values were added to the powder mixture. Results of XRD and SEM showed that during mechanical activation, the reduction was completed after 36 hours and when 3/4 times of Al stoichiometric value was added. At the third stage of experiments, simultaneous reductions of Co and Cr oxides with graphite and 3/4 times of pure Al stoichiometric value to produce Co-20%Cr was investigated. XRD results indicated that after 12 hours of mechanical milling, reduction reactions were completed so that picks of primary materials were totally removed and picks of Co, Cr and Alumina were appeared. It was observed that an increase in milling time to 36 hours causes a decrease in the size of producing particles and agglomerates. Studying the products by sem showed that Co-Cr alloy was formed with alpha-Al2O3 particles. Also, in this section, the effect of different amounts of carbon on the products was investigated. Results showed that graphite acts as PCA and prevents particles from sticking together. in the last section, simultaneous reductions of Co and Cr oxides was studied in the presence of Al and absence of graphite. In this stage, we encountered the problems such as sticking of materials to the milling container and formation of small clogs that adding 1 weight percent of graphite charge and 1-3 weight percent of the total charge of stearic acid powder as PCA respectively didn't solve the above problems.
Keywords: Mechanical alloying, Mechanochemical Reduction, Simultaneous reduction of cobalt and chromium oxides, Co-Cr alloy, Aluminothermic of cobalt and chromium oxides
