AbstractsChemistry

The objective of this research project is to investigate the corrosion behavior of Cu-Zr-Al metallic glasses and the effects of the addition of alloying elements as well as their structural changes on their corrosion behavior. Cu95-xZrxAl5 (x = 40, 42.5 & 45 at%) metallic glasses have been used to investigate the corrosion behavior of the Cu-Zr-Al metallic glasses with various compositions. Two series of Cu-based metallic glasses namely, Cu55-xZr40Al5Nbx (x = 1, 3 & 5 at%) and Cu50-xZr45Al5Nbx (x = 1, 3 & 5 at%) metallic glasses have been used to study the effect of the addition of Nb on their corrosion resistance. On the other hand, Cu50Zr45-xTixAl5 (x = 0, 2.5 & 5 at%) metallic glasses have been employed to investigate the effect of Ti on its corrosion resistance. Finally, Cu50Zr45Al5 bulk metallic glass (BMG) has been used to illustrate the influence of structural changes, i.e. crystallization, on its corrosion resistance. Thermal stability of the metallic glasses have been compared by comparing their glass transition temperature (Tg) and onset temperature of crystallization (Tx) as well as their supercooled liquid region (ΔTx = Tx - Tg) measured with differential scanning calorimetry (DSC). The metallic glasses were scanned from 323K to 873K at a heating rate of 0.67 K/s. According to the measured supercooled liquid regions, slight decrement resulted from the addition of Nb and Ti to the metallic glasses. However, the alloys still have high glass-forming abilities and can be cast into bulk glassy sample. The corrosion behavior of the metallic glasses has been investigated with immersion tests and potentiodynamic polarization measurements in 1N HCl, 3% NaCl and 1N H2SO4 solutions at 298K and opened to air. In addition, the surface morphology of the corroded samples was observed. From the results, it is found that the addition of Nb and Ti to the metallic glasses is effective in improving their corrosion resistance. The effect of alloying elements on the corrosion behavior of the metallic glasses is discussed. In order to understand the influence of the structural changes on the corrosion behavior of the metallic glasses, the metallic glasses were annealed for 240 and 300 seconds at 720K, which is between the glass transition temperature and the onset temperature of crystallization. The annealing treatments lead to nano-crystalline and crystalline microstructure respectively. From the results of the corrosion tests, it is found that the partially crystallized sample has the best corrosion resistance in all solutions, which means that the partial devitrification of the metallic glasses improves the corrosion resistance of the metallic glasses. CityU Call Number: TN693.M4 T35 2005 x, 98 leaves : ill. ; 30 cm.