Influence Of Heat History On Glass-forming Ability And Property Of Amorphous Alloys

In this paper, Gd-based and Sm-based were chosen to research the influence of heat history on the glass forming ability, the thermal expansion behavior, oxidation behavior and the hardness. The relation among the heat history, local ordering regions and property was discussed, which displayed the relativity between structure of liquid and the structure of solid.The bulk metallic glassy rods Gd55Al25Cu10Co10 of 2mm in diameter were prepared using copper mold suction casting method at different superheated temperatures. Glass forming ability and thermal expansion behavior of nominal compositions Gd55Al25Cu10Co10 bulk metallic glasses (BMGs) are investigated using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), high resolution transmission electron microscopy (HRTEM) and thermal dilatometer. It was found that the glass forming ability gradually increased with increasing melt superheated temperature and reached the maximum at 1105℃. In addition, the study on thermal expansion behavior revealed that the average thermal expansion coefficient decreased with increasing melt superheated temperature and at 1105℃. After melt superheated treatment, the melt structure become more homogeneous, local ordering regions turn into much smaller and thermal stability is enhanced. The as-quenched samples are just to inherit liquid structure after melt superheated treatment, thus the glass forming ability of as-quenched samples increases with increasing superheated temperature.The Gd56Al26Co18 and Sm56Al26Co18 were chosen to research the influence of remelting treatment on the glass forming ability and thermal expansion behavior using X-ray diffraction (XRD), differential scanning calorimetry (DSC), dilatometer and high resolution transmission electron microscopy (HRTEM). The results showed that the remelting treatment can improve the glass forming ability of the alloys. In addition, it was found that the average thermal expansion coefficients of the BMGs prepared by remelting were smaller than the BMGs prepared by first-time melting for Gd56Al26Co18 and Sm56Al26Co18 alloys. After remelting treatment, the microstructure of the amorhous alloys become more homogeneous and local ordering regions turn into much smaller. Therefore, the glass forming ability and thermal stability of amorphous alloys were enhanced.The influence of remelting treatment on the oxidation behavior and the hardness of Sm56Al26Co18 amorphous alloys, was investigated by therm-gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD) and hardness test apparatus. It was found that the remelting treatment can improved the oxidation resistance and hardness of Sm56Al26Co18 amorphous alloy, which has closely related with the more even microstructure.