Microstructure Examination of the Zr₆₅Al₁₀Ni₁₀Cu₁₅ Bulk Metallic Glass after Superplastic Gas-Pressure Forming

摘要

Microstructure and crystallinity during superplastic gas-pressure forming of the Zr₆₅Al₁₀Ni₁₀Cu₁₅ bulk metallic glass sheet fabricated by squeeze copper-mold casting method was examined. A small degree of crystallization (5.7～8.7 vol.%) was found to occur during the forming, though the sum of heating and holding time for the sample and forming time was controlled to be much less than the onset time of crystallization predicted by the T.T.T diagram of the metallic glass sheet. The degree of crystallization depended on position of the deformed body, which was highest as the apex where the largest straining took place, indicating acceleration of crystallization kinetics during plastic flow. The SRC test at 696K performed in tension repeated for four times consecutively on a given sample suggested that superplastic-flow behavior of the metallic glass sheet would not have been significantly affected by crystallization during gas blow forming.