Nanometer-Scale Structure and Dynamics of Bulk Metallic Glass Forming Alloys from Coherent Nanodiffraction

Departments: Mechanical Engineering and Materials Science
Time: Wednesday, February 11, 2015 - 2:30pm - 3:30pm
Type: Seminar Series
Presenter: Paul M. Voyles
Room/Office:
Location:
Mason
9 Hillhouse Avenue - Rm. 107
New Haven, CT 06510
United States
See map: Google Maps

Nanometer-Scale Structure and Dynamics of Bulk Metallic Glass Forming Alloys from Coherent Nanodiffraction

Paul M. Voyles

Department of Materials Science and Engineering, University of Wisconsin-Madison

1509 University Ave, Madison, WI 53706

 

Abstract:

 

We have used coherent electron nanodiffraction in a scanning transmission electron microscope to investigate the structure and dynamics of various bulk metallic glass (BMG) forming alloys.  Spatial variations in nanodiffraction reveal nanometer-scale structure in a technique called fluctuation electron microscopy (FEM).  By combining FEM with computational structure refinements, we have shown that Zr-Cu-Al BMGs contain two competing nanoscale structure types [1].  One is icosahedral, with approximate five-fold rotational symmetry.  The other is more crystal-like four- and six-folder rotational symmetry.  The stability of these structures on annealing is correlated to glass forming ability (GFA).  In Zr50Cu45Al5, an alloy with high GFA, annealing increases the icosahedral structure.  In Zr50Cu35Al15, an alloy with lower GFA, annealing increases the crystal-like structure.  Time variation in nanodiffraction from alloys heated into the supercooled liquid state inside the STEM reveal the dynamics of atomic rearrangements with nanometer spatial resolution in a technique called electron correlation microscopy (ECM).  Initial ECM data on Pd40Ni20P20 BMG show an a relaxation time as a function of temperature in approximate agreement with mechanical spectroscopy data and offer a glimpse of spatial variability in ta from the time-dependent scattering of single coherent speckles [2].

[1] J. Hwang, Z. Melgarejo, Y. E. Kalay, I. Kalay, M. J. Kramer, D. S. Stone, P. M. Voyles, P. M. Phys. Rev. Lett.108, 195505 (2012).

[2] L. He, P. Zhang, M. Besser, M. J. Kramer, P. M. Voyles (submitted).

 

Wednesday, February 11, 2015

2:30 – 3:30 pm

 

Location – Mason 107

Host:   Professor Judy Cha

 

Refreshments served at 2:15 pm