On the phase transitions of the quasicrystalline phases in the Al-Cu-Fe-Co alloy

摘要

Microstructural change with Co content together with heat treatment was studied in rapidly solidified Al-Cu-Fe-Co alloys using X-ray diffractometry and transmission electron microscopy. With an increase in Co content in the as-cast Al_(65)Cu_(20)Fe_(15-x)Co_x alloys, the relative amount of the icosahedral phase drastically decreased and that of the decagonal phase increased. In the as-melt spun alloys, effects of Co content are critically changed at around 5 at percent Co. For the less Co containing alloys (below 5 at percent), the icosahedral phase proved to be the major phase, while the 5 at percent Co containing alloy showed the coexistence of the icosahedral and decagonal phases. The 8 at percent containing alloy showed the monolithic decagonal phase in the as-melt spun state. unlike as-cast alloys, all the as-melt spun alloys showed no trace of the lambda-phase. However, after heat treatment of ribbons, lambda-phase newly appeared in the Al_(65)Cu_(20)Fe_(10)Co_3 and Al_(65)Cu_(20)Fe_(10)Co_5 alloys. The lambda-phase showed orientation relationships with surrounding icosahedral or decagonal phases.