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2 Materials Science Poland

2 2009

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Structure and crystallization kinetics of amorphous Al-Ni-Si alloy

Gögebakan M., Okumus M.

Materials Science Poland

2009

Vol. 27, No. 1

79--87

In the present work, the structure and crystallization kinetics of rapidly solidified Al70Ni13Si17 amorphous alloy have been investigated by a combination of differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). Amorphous ribbons were obtained by melt spinning at wheel speeds higher than 10 m/s. Crystallization of amorphous Al70Ni13Si17 alloy during continuous heating in DSC, takes places in three stages: (1) formation of fcc-Al and hexagonal phases; (2) growth of fcc-Al and hexagonal phases; (3) formation of fcc-Si and orthorhombic Al3Ni phases. Isothermal annealing DSC traces for this amorphous alloy, the first crystallization peak showed a clear incubation period, and the Avrami time exponent n has been determined to be 2.4-2.8 using the Johnson-Melh-Avrami analysis. This suggested that the transformation reaction involved continuous nucleation and three dimensional diffusioncontrolled growth. Electrical resistivity of the alloy was measured as 33x10-6 ? cm for the amorphous structure and 1x10-6 ? cm for the crystalline one. This study describes the structure and crystallization kinetics of a rapidly solidified Al70Ni13Si17 amorphous alloy.

Quasicrystalline phase formation in the conventionally solidified Al-Cu-Fe system

Gögebakan M., Avar B., Uzun O.

Materials Science Poland

2009

Vol. 27, No. 3

919--926

Structural characteristics and thermal behaviour of the conventionally solidified Al-Cu-Fe alloys with nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 were investigated by X-ray diffraction, scanning electron microscopy, and differential thermal analysis techniques. Results show that a single quasicrystalline phase forms in a conventionally solidified Al65Cu20Fe15 alloy, being thermodynamically stable without phase transition up to the melting point. A cubic AlFe(Cu) solid solution, identified as ß phase, and a cubic AlCu(Fe) solid solution, identified as ? phase, were observed with quasicrystalline phase for Al63Cu25Fe12 alloy. Conventional solidification of Al70Cu20Fe10 alloy does not result in quasicrystalline phase formation. However, the formation of quasicrystalline phase in conventionally solidified Al70Cu20Fe10 alloy was observed after additional annealing at elevated temperature. SEM micrographs for Al70Cu20Fe10 and Al63Cu25Fe12 alloys after annealing at 700 °C for 4 h revealed the formation of pentagonal dodecahedrons in the quasicrystalline phase, with an edge size of about 30 žm.