Long-Range Mass Transport during Structural Transitions in Metallic Glass-Forming Melts

Abstract

We investigate the structure and dynamics of the bulk metallic glass-forming alloys Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 and Zr 58.5 Cu 15.6 Ni 12.8 Al 10.3 Nb 2.8 . Combining in situ synchrotron x-ray diffraction and quasielastic neutron scattering with electrostatic levitation, we directly observe an abrupt change in the temperature dependence of the first structure factor maximum of these melts. We find that the kinetics of this liquid-liquid transition during cooling are on the order of tens of seconds, whereas its onset temperature depends only weakly on the applied cooling rate. Such slow transition kinetics require longrange mass transport, which is incompatible with a transition mechanism involving only local structural changes as in oxides or molecular liquids.

Freezing Shrinkage Dynamics and Surface Dendritic Growth of Floating Refractory Alloy Droplets in Outer Space

“…Both the International Space Station (ISS) and CSS are supplied with experimental equipment to study the alloy solidification under microgravity and containerless conditions. [12,13] Electrostatic levitation (ESL) has been widely used in solidification experiments, most of which are carried out by ground-based ESL equipment, [14][15][16][17] while a small number of which are carried out on ISS. [18] Compared to electromagnetic levitation, ESL lacks electromagnetic stirring within the molten materials, which is advantageous for studying deep undercooling and rapid solidification of liquid alloys.…”

Electromagnetic levitation containerless processing of metallic materials in microgravity: thermophysical properties

“…Recent examples are Cu-Ni 43 , Si-Ge 44 , or ZrNi 41 where, at deep undercoolings, a significant deviation of the specific resistivity from linearity is observed or even a sign reversal of the temperature coefficient. Moreover, from investigating the undercooled range, indications of a liquid-liquid phase transition became evident in a number of properties in liquid Vit1 and Vit106a 45 , 46 .…”

Glassy or Amorphous? A Demonstration Using G-Phase Copper Containing a Fivefold Twinning Structure

“…Despite the fact that liquid–liquid transitions (LLTs) have been reported in many substances like amorphous ice, amorphous silicon, molecular liquids, , and oxide glass, their emergence in metallic glass-forming systems − is both surprising and intriguing. Unlike other systems that have directional bonding (e.g., hydrogen bonds), metallic glasses (MGs) are considered to have nondirectional metallic bonds that are not expected to stabilize the second liquid phase.…”

“…It is then a surprise to see many MGs have signs of LLTs, as detected by different experimental techniques, in their molten liquids or supercooled liquids. These signs include abrupt changes in the structural factor or radial distribution function (RDF), 4,7,13,14,16 the appearance of anomalous calorimetry peaks, 13 and a kink in the Knight shift. 10 However, the reported LLTs are all in multicomponent MGs, which are more likely to have phase separation rather than phase transition upon cooling from the melts.…”