# Research Activity: Mechanical Behavior of Materials and Radiation Effects

Division: Materials Sciences and Engineering

Primary Contact(s): Yok Chen ([yok.chen@science.doe.gov]{.underline};
301-903-4174)

Team Leader: Robert J. Gottschall

Division Director: Patricia Dehmer, Acting

**Portfolio Description:**

This activity focuses on understanding the mechanical behavior of
materials under static and dynamic stresses and the effects of radiation
on materials properties and behavior. The objective is to understand the
defect-behavior relationship at an atomic level. In the area of
mechanical behavior, the research aims to advance understanding of
deformation and fracture and to develop predictive models for design of
materials having desired mechanical behavior. In the area of radiation
effects, the research aims to advance understanding of mechanisms of
amorphization (transition from crystalline to a non-crystalline phase),
understand mechanisms of radiation damage, predict and learn how to
suppress radiation damage, develop radiation-tolerant materials, and
modify surfaces by ion implantation.

**Unique Aspects:**

This activity represents a major fraction of federally supported basic
research in mechanical behavior and is the sole source of basic research
in radiation damage. In the science of mechanical behavior, cutting-edge
experimental and computational tools are bringing about a renaissance,
such that researchers are now beginning to develop unified,
first-principles models of deformation, fracture, and damage. The
compelling need for understanding deformation mechanisms is related to
the fact that virtually all structural metals utilized in energy systems
are fabricated to desired forms and shapes by deformation processes. The
compelling need in radiation effects - for valid predictive models to
forecast the long-term degradation of reactor components and radioactive
waste hosts - is expected to become increasingly critical over the next
decade. Radiation tolerance of structural metals and insulating ceramics
is also a matter of great concern for fusion energy systems.

**Relationship to Others:**

This research activity forms the basis for:

\- The activities of these centers include concerted outreach effort
coordinating the science with Small Business Innovation Business (SBIR)
program on topics such as surface modification by ion implantation,
metal forming, oxide protective films on metals, high-temperature
intermetallic alloys, and corrosion.

\- This CRA also coordinates with DOE's Office of Defense Programs (DP)
on the multi-institutional collaborative Nansoscience Network topic
entitled "Mechanics and Tribology at the Nanoscale."

Other parts of DOE:

\- Nuclear Energy Research Initiative (NERI)

\- Energy Materials Coordinating Committee (EMaCC)

Interagency:

\- MatTec Communications Group on Metals

\- MatTec Communications Group on Structural Ceramics

\- MatTec Communications Group on Nondestructive Evaluation

\- Interagency Working Group on Nanotechnology

**Significant Accomplishments:**

Ordered intermetallic alloys based on aluminides and silicides have
great potential for structural use at high temperatures because of their
excellent mechanical strength and corrosion resistance. However, because
they lack ductility, they are generally brittle and impossible to
fabricate by conventional techniques such as rolling, forging,
extruding, drawing or sheet forming at ambient temperatures. Clear
evidence has now been developed over the past twenty years of work under
this activity that many intermetallic alloys are intrinsically quite
ductile; the observed poor ductility and inability to fabricate them is
now understood to arise from moisture-induced embrittlement. The
understanding of the embrittlement mechanism has led to the formulation
of scientific alloying and processing principles that have now proved to
be effective in the design of ductile intermetallic alloys for
commercial use. This cumulative work has led to eight commercial
licenses and has been recognized by the Department of Energy\'s E. O.
Lawrence Award, the Acta Metallurgica Gold Medal, two Humboldt (Germany)
awards and numerous other honors to the investigators that have been
involved.

Magnetism affects hardness? Experimental studies and first-principals
theoretical calculations of a model intermetallic system have identified
magnetic interactions as the cause of the unusually large lattice
dilation and resultant solid solution softening in NiAl alloyed with Fe
solutes. Solid solution hardening is an important element in the design
of metallic materials as strength elements for structural use. The
hardening behavior of random substitutional solid solution has
traditionally been correlated with a mismatch in atomic size or elastic
moduli, and/or difference in valence electrons between solute and
solvent atoms. The solid-solution effect in ordered intermetallic
alloys, however, is much more complex and not well understood because
hardening behavior of intermetallics requires the consideration of both
site occupancy and excess point defects induced by solute atoms.

Another effort in this activity is focused on the understanding and
development of radiation-tolerant materials, which have critical
implications for environmentally acceptable and reliable nuclear-waste
storage. Experiments have shown that a class of complex oxides,
gadolinium zirconate, will lock plutonium in its structure and remain
highly resistant to the radiation damage from radioactive plutonium for
hundred thousands of years. Current materials proposed for plutonium
immobilization become unstable in several decades and eventually the
plutonium will leach into the environment. In parallel studies, the
ability to theoretically predict the composition and structure of
radiation-tolerant materials has been formulated on a scientific basis.
The research in this area has contributed to a Guggenheim Fellowship
Award, Canada's Hawley Medal, and a Distinguished Scholar Award from the
Microbeam Analysis Society.

Materials Friendly to Nuclear Waste: The ability to predict the
composition and structure of materials that are resistant to radiation
damage, such as in nuclear waste storage, has been formulated on a firm
scientific basis. Current nuclear storage materials cannot resist
radiation damage for the required thousands of years, because
radioactive emissions in a storage material jostle atoms out of their
carefully ordered arrangements. These materials become unstable, and
eventually leach into the environment. Computer simulations and
experiments revealed that a special class of complex ceramic oxides
called *fluorites* is able to resist this fate. This class of materials
shares a basic chemical formula: two different pairs of metallic ions
and seven oxygen atoms. The fundamental principle is rather simple: The
configurations of atomic arrangements in these oxides are relatively
disordered which explains why they can easily tolerate displaced atoms
caused by radiation. Like an out-of-place object in a messy household, a
misplaced atom into an anti-site is not all that conspicuous.

Dialing Friction? In the U.S. alone, an estimated \$1.9 billion/year in
energy is wasted to fight friction. The trick to controlling friction
between microscopic moving parts is to coat them with molecules that
spontaneously order into a single layer like the bristles on a brush.
Experiments using a unique Interfacial Force Microscope to delicately
rub together different layer combinations showed how chemical
interactions both within the brush-like layer and across the moving
interface determine friction. Alkanethiol molecules with chemically
inert ends self-assemble into a passive, Teflon-like surface with
remarkably low friction due only to the physical waving motion of the
\"bristles.\" Substituting chemically active ends on the same molecules
introduces attractive forces that increase friction. These attractive
forces can be fine-tuned by changing the molecule length, which
effectively points the end group in a different direction and
consequently "dials-in" the amount of friction.

**Mission Relevance:**

The scientific results of this activity contribute to the DOE mission in
the areas of fossil energy, fusion energy, nuclear energy,
transportation systems, industrial technologies, defense programs,
radioactive waste storage, energy efficiency, and environmental
management. In an age when economics require life extension of
materials, and environmental and safety concerns demand reliability, the
ability to predict performance from a fundamental basis is a priority.
Furthermore, high energy-conversion efficiency requires materials that
maintain their structural integrity at high operating temperatures. It
is also necessary to understand the deformation behavior of structural
metals so as to fabricate them to desired forms and shapes. This
activity seeks to understand the mechanical behavior of materials. It
also relates to nuclear technologies including fusion, radioactive waste
storage and extending the reliability and safe lifetime of nuclear
facilities. For example, a recent study to understand environmental
cracking of metallic alloys on the atomic scale has strong implications
in pressurized water reactors.

**Scientific Challenges**:

There are two grand challenges: (a) Understanding the mechanism of
amorphization at the atomic scale when oxides are irradiated with
neutrons or positive ions. Amorphization degrades a material and
adversely affects its physical and chemical properties. By understanding
the mechanism and the parameters contributing to radiation tolerance, it
will be possible to predict or engineer materials that are less
susceptible to amorphization by radiation damage. (b) A unified model
covering all length scales that can successfully explain deformation and
fracture. Dislocation theory is typically valid for length scales less
than 0.1 micron. Continuum elasticity and constitutive equations derived
from it are typically limited to macroscopic length scales greater than
10 microns. These models do not converge in the interval often referred
to as "mesoscale" between these limits. It is often possible, however,
to control or \"tune\" microstructural features in this mesoscale regime
by suitable adjustment of synthesis and processing parameters. Thus a
unified model is sought that will quantitatively describe mechanical
behavior (including strength, deformation parameters, and fracture
toughness) over all length scales. A unified predictive model that is
valid in the mesoscale regime could be used to design microstructures
that could then be achieved via appropriate selection of synthesis and
processing parameters and thus lead to optimized materials properties
and behavior. Other challenges are: (a) Many metals and metallic alloys,
including common steels, undergo a profound ductile-to-brittle
transition over a small temperature interval, without structural or
chemical change. The understanding of the origins of this transition
remains elusive and represents an on-going challenge. (b) Investigating
and understanding nanoscale materials, their response to mechanical
stress and radiation damage, will reveal previously inaccessible realms
of materials behavior as well as paving the way to novel applications.

**Funding Summary:**

**Dollars in Thousands**

**[FY 2002]{.underline}** **[FY 2003 Request]{.underline}** **[FY 2004
Request]{.underline}**

14,530 14,530 14,510

> **[Performer]{.underline} [Funding Percentage]{.underline}**
>
> DOE Laboratories 81.7%
>
> Universities 18.3%
>
> These are percentages of the operating research expenditures in this
> area; they do not contain laboratory capital equipment,
> infrastructure, or other non-operating components.

**Projected Evolution:**

Predicting the elemental, stoichiometric, and structural combinations
that will yield radiation-tolerant materials by design is likely to make
strong progress, thus ending an era of empirical and trial-and-error
design. The Nanoscience Network project on "Tribology at the Nanoscale"
leverages both BES and DP investments. The materials-by-design approach
at the nanoscale level, and the time-and-length scale of the experiments
necessary to link with models, will require state-of-the-art
microscopies and innovative techniques.

In the long term, we anticipate continued efforts to develop a unified
model covering all length scales that will provide significant insights
into deformation and fracture. Concurrent advances in microstructural
characterization will be exploited to understand the ductile-to-brittle
transition and permit this understanding to be exploited for the design
of embrittlement-resistant materials. The origins of radiation tolerance
will continue to be pursued including exploitation of parameters, which
feed into the phenomena of radiation tolerance, such as structure,
stoichiometry, and ionic (or atomic) size. Advanced computer simulations
for modeling radiation-induced degradation developed during this time
will also be essential to progress. During this time, the mesoscale and
nanoscale modeling efforts will be extended to include nanoscale
materials.

It is envisioned that nanomechanics will occupy the stage in the next
decade. It will be impacted especially by the fundamental understanding
of quasi zero-dimensional clusters of atoms. Nanoclusters involve small
assemblies of atoms and can be envisioned as constituting the third
dimension of the periodic table. Nanocluster research will evolve with
its own spectroscopy and magic numbers. Such understanding is expected
to have profound effects on sub-fields such as MEMS and NEMS.

November 12, 2023