Ruthenium Aluminides: Deformation Mechanisms and Substructure Development Page: 3 of 13
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Structural and functional materials that can operate in severe, high temperature
environments are key to the operation of a wide range of energy generation systems.
Because continued improvements in the energy efficiency of these systems is critical,
the need for new materials with higher temperature capabilities is inevitable.
Intermetallic compounds, with strong bonding and generally high melting points offer this
possibility for a broad array of components such as coatings, electrode materials,
actuators and/or structural elements. For most applications some degree of intrinsic
deformability is desirable for durability under thermal cycling conditions.
RuAI is a very unusual intermetallic compound among the large number of B2
compounds that have been identified and investigated to date. This material has a very
high melting temperature of 20500C, low thermal expansion, high thermal conductivity
and good corrosion resistance. Unlike most other high temperature B2 intermetallics,
RuAI possesses good intrinsic deformability at low temperatures [1 - 8 ]. In this program,
fundamental aspects of low and high temperature mechanical properties and
deformation mechanisms in binary and higher order RuAI-based systems have been
investigated. Alloying additions of interest included platinum, boron and niobium.
Additionally, preliminary studies on high temperature oxidation behavior of these
materials have been conducted.
In comparison to other B2 compounds, a number of unusual features of the behavior of
this class of intermetallics have been discovered. TEM studies of stoichiometric RuAI
indicate that deformation occurs by glide of both <100> and <011> dislocations within
individual grains, giving five independent slip systems. These slip systems operate over
a wide range of temperature, from -1960C to 10500C. Additionally, the addition of 2at%
Pt results in a transition to <111> slip. No other high melting point B2 intermetallic is
known to deform by any of these slip modes. Additionally, preliminary high temperature
creep experiments demonstrate an exceptionally high creep strength for RuAI at 10500C.
For a fixed creep rate RuAI can sustain stresses that are approximately a factor of 25X
higher, compared to NiAI. The oxidation properties are also very unusual, with the
formation of alternating layers of A12O3 and 6-Ru as a result of exposures in the
temperature range of 10000C - 12000C. Pt additions provided substantial improvements
in oxidation rates. A more in-depth description of the research is provided in the
following sections. Additional details are given in manuscripts published as a result of
this research program, listed in Section 6.
2. Slip Systems in RuAI - Low Temperatures
All experiments have been performed on polycrystalline RuAI alloys prepared by arc-
melting or levitation melting, following by annealing at either 13000C or 15000C. To first
understand the unusual low temperature deformation behavior of this class of materials,
detailed transmission electron microscopy studies were conducted on polycrystalline
RuAI deformed at room temperature and 77K. Fig. 2(a) shows a low magnification view
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Pollock, Tresa M. Ruthenium Aluminides: Deformation Mechanisms and Substructure Development, report, May 11, 2005; Ann Arbor, Michigan. (digital.library.unt.edu/ark:/67531/metadc877902/m1/3/: accessed February 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.