Intermetallic sheets synthesized from elemental Ti, AI, and Nb foils
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Intermetallic Sheets Synthesized from Elemental Ti, AI, and Nb Foils D.E. ALMAN and C.P. DOGAN Low density, combined with relatively good high-temperature strength, has made titanium aluminides the focus of interest of the aircraft industry for a number of years. Recently, ternary additions of niobium have been found to enhance Ti3Al's strength-to-density ratio and to improve its room-temperature ductility while retaining its high-temperature strengthY ~1 However, in order to find widespread application, these materials must not only have the desired physical properties but must also be fairly inexpensive and easy to produce. Unfortunately, in spite of their improved properties, these ordered intermetallic compounds are still relatively brittle and therefore difficult to shape via conventional hot and cold deformation processing. One potentially promising processing route for these materials is self-propagating, high-temperature synthesis (SHS). It has been demonstrated, for example, that an SHS reaction can be initiated between elemental metal foils to produce intermetallic compounds.tS] This foil-SHS technique has been subsequently employed by the United States Bureau of Mines researchers to produce a variety of metalintermetallic lamellar sheet composites based on the Ni-A1 and Ti-A1 systems.[6,7,81 Through selection of appropriate foil thicknesses and processing parameters, monolithic NiA1 foils approximately 150%tm thick can also be produced from Ni and AI foils.t6] A key advantage to this tech-
D.E. ALMAN and C.P. DO(~AN, Materials Research Engineers, are with the Materials Science Division, United States Bureau of Mines, Albany Research Center, Albany, OR 97321. Manuscript submitted December 29, 1994. METALLURGICALAND MATERIALSTRANSACTIONSA
Stocking Sequence B
Stocking Sequence A Ti =
0.025
AI =
0.01
Ti =
0.025
AI =
0.01
Nb
=
0.025
AI
=
0.01
Ti =
0.025
AI =
0.01
Ti =
0.025
AI =
0.01
0.025 0.01
mm
Ti =
0.05
mm
=
AI =
0.01
mm
0.025
AI =
0.01
Ti =
0.025
0.025 0.01
Ti --- 0 . 0 2 5 At
=
mm mm mm mm mm mm
mm
AI =
Nb
mm mm
mm AI =
=
mm
mm Nb
Nb
mm
mm mm rnm
(a)
=
0.01
Ti =
0.025
AI =
0.01
Nb
=
0.025
AI =
0.01
Ti =
0.025
mm mm mm mm mm mm rnm
(b)
Fig. 1--Stacking sequence of elemental Ti, A1, and Nb used to make the Ti-A1-Nb intermetallic alloy sheets: (a) stacking sequence A, corresponding to a composition of Ti-23A1-25Nb (at. pct); and (b) stacking sequence B, corresponding to a composition of Ti-24A1-23Nb.
nique is that the difficulties associated with the thermomechanical processing of brittle aluminides are avoided. In addition, the elemental foils can be plastically formed into complex shapes prior to synthesizing the brittle aluminide~ To date, research has focused on using this method to produce binary intermetallics; this study demonstrates that more complicated ternary aluminides, such as the Nb-modified Ti3A1 alloys, can also be produced directly from elemental foils. Commercially available Ti (0.025-mm or 0.050-mmthick), Nb (0.025-mm
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