Containerless processing of the undercooled metallic melts — overview

Abstract

Brief overview of current containerless electrostatic levitation processing technique and research progress of the area of bulk metallic glass formation is introduced. Undercooling behavior during solidification of the bulk metallic glass forming Zh~ :Til~.sCu~,,.sNi~0,Be2z, alloy has been studied using the containerless electrostatic levitation processing technique. The melt is successfully undercoolcd to the glass transition temperature forming the amorphous phase with the proper thermal treatment. Differential scanning calorimetry (DSC) is used to determine the Gibbs free energy difference between the crystal and the undercooled liquid. The results indicate that the Gibbs free energy difference between the metastable undercooled liquid and the crystalline solid of the Zr4~:Tit~RCuzzsNi~arjB~,_, alloy is relatively small compared to that of conventional metallic glass forming binary, alloys even for large undercoolings. The hemispherical total emissivity of undercooled liquid is measured in the whole region of undercooled liquid state. Due to the combining effects of excellent thermal stability of the undercooled liquid in the Zr4, _,.Ti13.,Cu~zsNi~0.nBcz~.~ alloy with unique experimental technique of the containerless electrostatic levitation processing, it is possible to construct the complete time-temperature-transformation ('ITr) diagram. The measured TIT diagram exhibiting the expected "C"shape can not be satisfactorily explained by the existing models due to the complex crystallization mechanisms.

Estimation of Glass Forming Ability of Amorphous Alloys Based on the Thermal Analysis Data during Cooling

“…These results are in good agreement with the experimental results of 15) which showed the nose time of 60 s and the nose temperature of 895 K. The critical cooling rate was calculated to be 1.7 K/s, which was also in good agreement with previous experimental result (1$2 K/s). 16) In order to generally describe the kinetics of phase transformation of amorphous alloys with a range of critical cooling rates, several theoretical approaches based on classical homogeneous nucleation theory have been undertaken. 10,11,17) However, there are large discrepancies between the theoretical model predictions and the experimental results.…”