Oxidation and Thermal Stability of Zr-based Bulk Metallic Glasses
| Autor: | Yan-Rong Chen, 陳妍蓉 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 The oxidation behavior and thermal stability of Zr-based bulk metallic glasses (BMGs), containing Zr53Ni23.5Al23.5（Zr3）and Zr58Cu22Al12Fe8 （Zr4）(in at. %) were studied over the temperature range of interest. The oxidation kinetics followed the multi-stage parabolic rate law, and the oxidation rate constants (kP values) of (Zr3) BMG at T≦500oC and (Zr4) BMG at T≦375℃ increased with temperature, but those values for Zr3 BMG gradually decreased with increasing temperature. It was found that the formation of m-ZrO2 (at T＞500℃) was responsible for the reduced oxidation rates, as compared to those of Zr4 BMG. The scales formed on the BMGs were composed mostly of tetragonal-(t-ZrO2) and monoclinic-ZrO2 (m-ZrO2) and minor Al2O3. The amorphous substrates transformed to crystalline phases were strongly dependent on composition. The crystallization sequence of Zr3 BMG is different from that of Zr4 BMG；the former alloy underwent the first crystallization of ZrNiAl, Zr2Al and Zr2Ni, and, then, followed by the oxidation reaction. Conversely, the Zr4 BMG started to form t-ZrO2, and then, followed by the crystallization of Zr2Cu and Zr2Al, and grow the Zr2Cu and Zr2Fe at the later stage of exposure. In addition, the pressure dependence of Zr3 BMG is nil over the temperature range of 450-500℃, indicating the scales of a typical N-type semi-conducting behavior. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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