Papers by Keyword: Supercooled Liquid Region

Abstract: Although a Ti47.4Zr5.3Ni5.3Cu42 glassy alloy does not occur precipitation of crystalline in annealing of prolonged time below glass transition temperature, it shows slightly embrittlement during passing through devitrification process. The embrittlment behavior may be connected to structural relaxation. Using ultrasonic, in this study, acoustic characteristics of the glassy alloy during progressive devitrification were examined in terms of structural relaxation. The structural changes are characterized by decreases in specific volume, bulk modulus, Lamè parameter and Poisson ratio, accompanied by structural relaxation.

Abstract: The compressive deformation behavior of as-cast Zr55.9Cu18.6Ta8Al7.5Ni10 Bulk Metallic Glass (BMG) composite with micro-scale particles of Ta-rich solid solution embedded in an amorphous matrix was investigated in the supercooled liquid region. It was found that the apparent viscosity of the BMG is dependent on temperature and strain rate. A deviation from a Newtonian behavior was observed at high strain rate and low temperature. The experimental results can be described by a master curve based on a stretched exponential function and the free volume theory. The structural state and the thermal ability of the BMG composite after deformation are also discussed in the paper.

Abstract: In the current study, the amorphization behavior of mechanically alloyed Ni57Zr20Ti22Pb1 powder was examined in details. The conventional X-ray diffraction results confirm that the fully amorphous powders formed after 5 hours of milling. The thermal stability of the Ni57Zr20Ti22Pb1 amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the glass transition temperature (Tg) and the crystallization temperature (Tx) are 760 K and 850 K, respectively. The supercooled liquid region

 is 90 K. The appearance of wide supercooled liquid region may be mainly due to the Pb additions which cause the increasing differences in atomic size of mechanically alloyed Ni57Zr20Ti22Pb1 powders.

Abstract: The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The thermal stability of the amorphous matrix is affected by the presence of the CNT particles. Changes in Tg and Tx suggest deviations in the chemical composition of the glassy matrix due to a partial dissolution of the CNT species in the amorphous phase. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ Ti50Cu28Ni15Sn7 metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

Abstract: Mg55Y15Cu30 metallic glass powders were prepared by the mechanical alloying of pure Mg, Y, and Cu after 10 h of milling. The thermal stability of these Mg55Y15Cu30 amorphous powders was investigated using the differential scanning calorimeter (DSC). Tg ,Tx , and Δ Tx are 442 K, 478 K, and 36 K, respectively. The as-milled Mg55Y15Cu30 powders were then consolidated by vacuum hot pressing into disk compacts with a diameter and thickness of 10 mm and 1 mm, respectively. This yielded bulk Mg55Y15Cu30 metallic glass with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix. The pressure applied during consolidation can enhance thermal stability and prolong the existence of amorphous phase within Mg55Y15Cu30 powders.

Abstract: The preparation of Mg49Y15Cu36 metallic glass composite powders was accomplished by mechanical alloying of pure Mg, Y, Cu, and WC powder mixture after 10 h milling. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Mg-based alloy glassy matrix. The metallic glass composites powders were found to exhibit a large supercooled liquid region before crystallization. Bulk metallic glass composites were formed by vacuum hot pressing the as-milled WC/ Mg49Y15Cu36 metallic glass composite powders at 473 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared under pressure of 1.20 GPa. It was found that the applied pressure during consolidation could enhance the thermal stability and promotes nanocrystallization of WC/ Mg49Y15Cu36 BMG composites.