GRADUATE STUDENT RESEARCH HIGHLIGHTS
2014 Spring Seminar Series
Friday, February 28, 2014
307 SERF Building
2:00 – 2:15
2:20 – 2:35
Haoling Jia
(Peter Liaw’s Research Group)
Dept. of Materials Science & Engineering
Insights from the lattice strain evolution on
deformation mechanisms in metallic-glass-matrix
composites
In-situ high energy synchrotron X-ray diffraction
experiments and micromechanics-based finite element
simulations have been conducted to examine the lattice
strain evolution in metallic-glass-matrix composites
(MGMCs) with dendritic crystalline phases dispersed in
the amorphous alloy matrix. The lattice strain
measurements show that the crystalline phase yields at
an applied stress of ~ 450 MPa and the metallic glass
matrix yields at ~ 1,450 MPa. The lattice strain
evolution curves are composed of the following three
stages. In Stage I, both the crystalline phase and matrix
are subjected to elastic deformation. In Stage II, the
matrix remains elastic but the crystalline phase deforms
plastically. In Stage III, plastic deformation features
both crystalline inclusion and amorphous matrix; at this
stage, relaxation of the lattice strains in the crystalline
phase occurs as the plastic deformation in the matrix
evolves. The micro-mechanisms corresponding to the
above stages are discussed in depth in the present work.
Ling Li
(Keppens/Mandrus’ Research Group)
Dept. of Materials Science & Engineering
Elastic softening and doping induced
ferromagnetism in quantum paraelectric
EuTiO3
The cubic to tetragonal phase transition at 105 K in
quantum paraelectric SrTiO3 has been extensively
studied for decades. Most recently, a similar structural
transition was observed near room temperature in
EuTiO3 which orders antiferromagnetically around 5 K.
The dramatic difference in structural transition
temperature and the close similarity in tolerance factor
between EuTiO3 and SrTiO3 attract much attention and
signal the importance of spin-phonon coupling in
EuTiO3. The observation of ferroelectricity and
ferromagnetism close to room temperature in EuTiO3
thin films further highlights the critical importance of
magnetism. In this talk, I will talk about (1) our
resonant ultrasound spectroscopy study of EuTiO3
single crystals in order to understand the nature of the
structural transition, and (2) chemical pressure effect on
the magnetism in polycrystalline EuTi1-xNbxO3 in order
to reveal the correlation between the low temperature
Eu magnetic order and high temperature structural
transition.
Join us for refreshments at
1:30 in 307 SERF
2:40 – 2:55
Jacob McMurray
(Ted Besmann’s Research Group)
Nuclear Engineering Dept. and Surface Processing
and Mechanics group leader in the Materials Science
and Technology Division at ORNL
Thermodynamic assessments of complex
uranium oxide systems using the CALPHAD
approach
The CALPHAD method is used to describe the
thermodynamic properties and phase relations in the UM-O system where M is a lanthanide, Th, or Y element.
The compound energy formalism (CEF) model for the
UO2±x phase can be extended to represent urania rare
earth solid solutions since. The lattice stability for
fictive MO2 fluorite structure compounds are calculated
from density functional theory (DFT) for use in the
CEF for U1-yMyO2±x. It is found that the introduction of
a U6+ cation into the CEF model results in a better
representation of the phase equilibria when M is a fixed
trivalent cation like many of the elements in the
lanthanide series. Tentative Gibbs functions for the
stoichiometric UM6O12 compounds are developed and
the partially ionic two-sublattice model is used to
represent the liquid phases. The models that constitute
the U-M-O assessments can be combined with those for
other actinide and fission product containing U-O
systems to develop higher order multi-component
representations within the CALPHAD framework.
Research supported by the US Department of Energy,
Office of Nuclear Energy, Fuel Cycle R&D Program.