Properties of in situ TiAl- and MoSi{sub 2}-base composites produced by reactive processing
- Bureau of Mines, Albany, OR (United States). Albany Research Center
- Oregon Graduate Inst. of Science and Technology, Beaverton, OR (United States)
A variety of intermetallic matrix composites can be produced in situ by Self-Propagating, High-Temperature Synthesis (SHS). In this particular US Bureau of Mines study, stoichiometric mixtures of elemental Ti and Al, with additions of either B, Si or C (graphite), were reactively hot-pressed to form TiAl, reinforced with 10 to 60 volume percent boride reinforcement, Ti{sub 5}Si{sub 3} or TiC. Similarly, Mo and Si powders were reacted with either C (graphite) powders or fibers to form MoSi{sub 2}-SiC composites. Microstructural evaluation of the TiAl-based composites revealed that the reaction products were predominantly TiAl with a range of complex boride phases (e.g., TiB, TiB{sub 2}, and AlB{sub 12}), Ti{sub 5}Si{sub 3}, or TiC, and with a small amounts of Ti{sub 3}Al, TiAl{sub 2}, and TiAl{sub 3} also present. In general, denser and more homogeneous composites were produced by initiating the reactions between elements under a modest pressure, followed by a post-reaction heat treatment at 1,000--1,200 C. Complete conversion of C to SiC, during in situ formation of MoSi{sub 2}-SiC, depended on the size of the graphite particles or fibers. Small graphite particles were completely converted to SiC, while the larger diameter graphite fibers were not. In the case of the larger diameter fibers, only the outer rim transformed to SiC, leaving an inner graphite core. Analysis of the room temperature hardness and abrasive wear of the composites indicated that the addition of a reinforcement phase improved both properties relative to similarly-processed monolithic compounds. In addition, the SHS synthesized materials had wear properties comparable to similar materials produced by conventional casting and hot isostatic processing methods. All the composites displayed active-passive corrosion resistance in both acidic and alkaline solutions.
- OSTI ID:
- 77964
- Report Number(s):
- CONF-950201--; ISBN 0-87339-283-3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM ALLOYS
ALUMINIUM BORIDES
BULK DENSITY
CHEMICAL REACTIONS
COMPOSITE MATERIALS
CORROSION
FABRICATION
FIBERS
HARDNESS
MICROSTRUCTURE
MOLYBDENUM SILICIDES
PARTICLES
SCANNING ELECTRON MICROSCOPY
SILICON CARBIDES
TITANIUM ALLOYS
TITANIUM BORIDES
TITANIUM CARBIDES
TITANIUM SILICIDES
TRANSMISSION ELECTRON MICROSCOPY
WEAR
X-RAY DIFFRACTION