High-Temperature Oxidation Behavior of Co- and FeCo-based Bulk Metallic Glasses

• Main Authors: Yuan-Hao Wu, 吳芫豪
• Other Authors: Wu Kai
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/71104720205095388162

碩士 === 國立臺灣海洋大學 === 材料工程研究所 === 100 === Air oxidation behavior of cobalt- and iron-cobalt-based bulk metallic glasses, containing [(Co50Cr15Mo14C15B6)97.5Er2.5]93Fe7 (Co7-BMG) and [(Fe50Co50)75B20Si5]96Nb4 (FeCo5-BMG) was studied in dry air over the temperature range of 600 ~ 700oC and 500 ~ 650oC, respectively. The results showed that the oxidation kinetics of the two BMGs followed the parabolic-rate law, indicating that diffusion is the rate-determining step during oxidation. The oxidation rate constants (kp values) gradually increased with increasing temperature, and it was found that kp values of Co7-BMG were better than those of FeCo5-BMG at 600 ~ 650oC. In general, the oxidation rates of the Co-based amorphous alloy were slower than those of pure cobalt by 3.7 ~ 3.9 orders of magnitude, indicating a better oxidation resistance of the Co7-BMG. The scales formed on the Co7-BMG consisted of CoO, Co3O4, CoMoO4, Cr2O3 and uncorroded Co3B. The formation of Co3B indicated that the crystallization of the amorphous substrate was occurred during oxidation. Very likely, the formation of CoMoO4 and Cr2O3 is responsible for the significant reduction of oxidation rates for the Co7-BMG, as compared to the faster oxidation rates of pure Co. In addition, the kp values of FeCo5-BMG were 0.88 ~ 1.02 orders of magnitude lower than the binary Fe50Co50 alloy, further indicating a better oxidation resistance of the FeCo5-BMG. The scales formed on the Fe50Co50 alloy consisted mostly of Fe3O4 and minor amounts of Fe2O3, while minor additional amounts of B2O3 and uncorroded α-FeCo were also observed on the FeCo5-BMG. It is most likely that the formation of B2O3 was responsible for the slower oxidation rates of the FeCo5-BMG, and the growth of α-FeCo further confirmed the occurrence of the substrate crystallization for the FeCo5-BMG during oxidation.