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  MSE / Research / Projects / Ruthenium Aluminides: Deformation Mechanisms and Substructure Development

Ruthenium Aluminides: Deformation Mechanisms and Substructure Development
Materials: Metals Ceramics
Application: Structural
Technique: Characterization

RuAl is a very unusual intermetallic compound among the large number of B2 compounds that have been identified and investigated in recent years. This material has a very high melting temperature of 2060˚C, low thermal expansion, high thermal conductivity and good corrosion resistance. Unlike most other high temperature B2 intermetallics, RuAl possesses good intrinsic deformability at low temperatures.

To gain insight to the origins of this unusual deformation behavior, our research has focused on investigation of slip modes and other key aspects of low temperature deformation in RuAl-based systems. These investigations have utilized binary, ternary and quaternary alloys in polycrystalline form. Transmission electron microscopy studies on RuAl deformed at room temperature and 77K reveal an unusual deformation substructure, with high densities of <110> and <100> dislocations on {110} planes. Combined slip on these two systems results in five independent slip systems, required for compatible deformation in a polycrystalline material. Strain rate change experiments also reveal a low strain rate sensitivity over a wide range of composition, indicating that alloying additions are not detrimental to the intrinsic deformation processes. Interestingly, we have also discovered that an addition of 2at%Pt to RuAl results in a change of the dominant deformation mode to slip on the <111>{110} system. This mode of deformation is typically only observed in B2 compounds with much lower melting temperatures and correspondingly lower ordering energies. Pt additions also improve the oxidation characteristics of this material in the temperature range of 1000-1200&#730;C.

The results to date highlight the possibility of a new class of ductile, high temperature B2 intermetallics. However, a number of key questions remain under investigation regarding the unusual behavior of these RuAl-based systems. The proposed program addresses these issues. First, it is unclear how the combined <110> + <100> dislocation substructure develops; transmission electron microscopy studies are in progress. Since this system is of interest as a material for thermal barrier coating systems, the high temperature creep properties are also important. Ternary Ni-Al-Ru alloys are under investigation.
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