Deformation and Fracture of Ruthenium Aluminide
Professor David Johnson
School of Materials Engineering
Funding: The National Science Foundation (Grant DMR-0076219)
RuAl-5%wt% Mo ingot pulled from a cold
crucible Czochralski furnace.
Intermetallics are often considered candidate materials for high temperature structural applications due to the high melting temperature and good oxidation resistance of many intermetallic compounds. However, problems with brittleness have not been solved for intermetallic systems that are to operate above the use temperature of the superalloys. Ruthenium aluminide, having the CsCl (B2) type crystal structure, is unusual in this respect, as good room temperature toughness has been reported from limited and qualitative tests. Previous experiments suggest that the unusual toughness originates from the multiplicity of slip along the <110> and <100> directions which differs considerably from that of most other B2 compounds in which the common slip directions are either <111> or <100>. Reasons, however, for this unusual deformation behavior have not yet been identified. This is likely due to the difficulty in processing single crystals and the exotic nature of the alloy. We propose to directly measure the deformation behavior and fracture toughness of RuAl using single crystals and multiphase composite microstructures of controlled orientation. Preliminary work has shown that appropriate materials for testing can be produced by cold crucible Czochralski techniques and by arc-zone melting . The primary goal for our research is to explain the deformation behavior of RuAl and to correlate the similarities and differences with that of other B2 compounds. With this knowledge, the underlying mechanisms for deformation and fracture can be identified and modeled which will lead to design strategies for improving the toughness of semi-brittle materials.
(a) Schematic of the RuAl-Mo pseudo-binary phase diagram, and
(b) the fully eutectic microtructure of a RuAl-5% wt% Mo Czochralski specimen (optical microscopy, longitudinal view).
S. Rosset, R. Cefalu, L. Varner, and D. Johnson, "Crystal growth of RuAl-base alloys," in High-Temperature Ordered Intermetallic Alloys IX,
J H. Schneibel et al
. eds, MRS, Pittsburgh PA (2001, accepted for publication).