Relations between Structure, Phase Formation and Phase Transitions in Supercooled Metallic Liquids and Glasses

Kenneth F. Kelton, Washington University, DMR 0856199

2 4 6 8 10 120.0

0.5

1.0

1.5

2.0

2.5

3.0

Pt20

Zr80

S(q)

q (inverse Angstroms)

Primary goal – study ordering in supercooled alloy liquids, particularly those that form metallic glasses, to develop a better understanding of glass formation and the glass transition.WU-BESL – construction of a new facility that is optimized for x-ray scattering studies of electrostatically levitated liquids was completed. A schematic of the vacuum chamber with scattering geometry is shown in the upper left figure and a levitated liquid sample is shown in the lower left. Pre-peak (indicated by arrow in figure below) indicates medium range order in a Pt20Zr80 liquid, an unusual feature in a highly mobile metallic liquid.

Density Measurement Light Source

X-Ray Scattered Cone

X-Ray Entrance

Position Laser 1

Position Laser 1

PSD 2

PSD 2

UV Light Source

Heating Laser 1

Heating Laser 2

Camera for Density Measurements

Pyrometer 1

Pyrometer 2

Visualization Optics

Area Detector

Relations between Structure, Phase Formation and Phase Transitions in Supercooled Metallic Liquids and Glasses (DMR-0856199)

Kenneth F. Kelton, Washington University, DMR 0856199

Graduate student Nick Mauro (left in figure) works with Austin Hope ( a Washington University freshman) on the levitation chamber.

Professor Kelton discussing Austin’s results in his analysis of x-ray scattering data.

Outreach - Kelton is a member and past president of UCSAC, a science advisory council dedicated to improving science education. As Chair of the Physics department at Washington University, Kelton has created an Outreach Committee that encourages and coordinates outreach activities of students (graduate and undergraduate) and faculty.

Broader Relevance -Results will be of basic and technological interest, leading to a deeper understanding of glass structure, phase transitions, and improved control over nanostructure production.

Graduate and Undergraduate Education

First Transparency – Intellectual Merit of Research

Our NSF sponsored research is focused on developing a better understanding of liquid and glass structures and how they impact glass formation and phase transitions in the glasses. Over the past year, we have designed and constructed a new electrostatic levitation (ESL) facility that is optimized for x-ray scattering studies of containerlessly processed liquids (WU-BESL, for Washington University Beamline ESL). Charged samples approximately 2-3 mm in diameter of metallic alloys are levitated in high vacuum by 3 sets of orthogonal electrodes using fast active feedback. These are melted using a high-power diode laser and the structure of the liquid is measured in transmission mode using synchrotron radiation. This facility will play a central role in the studies that will be carried out under our current NSF grant. The facility was successfully tested at the Advanced Photon Source in August, 2009. We also obtained structural data on several alloys, including those that form the Cu-Zr and Ni-Zr binary metallic glasses, Ti-Zr-Hf-Ni liquids that show a change in structure with Hf substitution for Zr, and the ones shown here, Pt-Zr.

Upper Left – Schematic diagram of the facility and the transmission geometry used for the scattering experiments.

Lower Left – Melted sample of Cu-Zr

Lower Right – X-ray structure factor for a Pt20Zr80 close to the melting temperature. Note the presence of the prepeak (indicated by arrow). This signals medium range order in the liquid. While medium range is sometimes observed in metallic glasses, to our knowledge this is the first time that it is has been observed in a metallic liquid. That the liquid is not deeply supercooled, but ordered near the melting temperature is even more surprising.

Kenneth F. Kelton, Washington University, DMR 0856199