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High-Temperature Oxidation Behavior of Co- and FeCo-based Bulk Metallic Glasses
|Authors: ||Yuan-Hao Wu|
|Contributors: ||NTOU:Institute of Materials Engineering|
[(Co50Cr15Mo14C15B6)97.5Er2.5]93Fe7;[(Fe50Co50)75B20Si5]96Nb4;bulk;bulk metallic glasses;oxidation rate
|Issue Date: ||2013-10-07T02:45:56Z
|Abstract: ||本研究主要探討鈷基和鐵鈷基非晶合金[(Co50Cr15Mo14C15B6)97.5Er2.5]93Fe7與[(Fe50Co50)75B20Si5]96Nb4 (分別簡稱Co7-BMG與FeCo5-BMG)，在600oC~700oC及500oC~650oC空氣下的氧化行為。研究結果顯示，兩種非晶合金的氧化動力學皆遵守拋物線律，其氧化反應速率常數值隨溫度上升而增加，顯示非晶的氧化是由固態擴散來主導。整體而言，Co7-BMG的氧化速率比純鈷慢約3.7~3.9個數量級，FeCo5-BMG的氧化速率比Fe50Co50慢約0.88~1.02個數量級，顯示兩種非晶合金擁有較佳的抗氧化性質。當兩種非晶合金在600~650oC相互比較彼此的kp值時，可以發現FeCo5-BMG之kp值比Co7-BMG快，因此可知Co7-BMG具有最佳的抗氧化性質。 Co7-BMG氧化後生成CoO、Co3O4、CoMoO4及Cr2O3的氧化物以及Co3B結晶相，其中生成Co3B相可知非晶基材經氧化後已有結晶反應，此外，比較純鈷氧化後生成CoO及Co3O4，推測生成CoMoO4與Cr2O3是非晶氧化速率降低的原因；另一方面，Fe50Co50經氧化後主要的氧化物為Fe3O4和表面少量的Fe2O3，並生成的結晶相為α-FeCo，但FeCo5-BMG更有少量的B2O3生成，因此推測生成B2O3是降低FeCo5-BMG氧化速率的主因。|
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.
|Appears in Collections:||[材料工程研究所] 博碩士論文|
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