On the growth of small fatigue cracks in {gamma}-based titanium aluminides
- Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering
Gamma-based TiAl intermetallic alloys have received considerable attention recently as candidate materials for high-temperature aerospace applications. Two classes of microstructure have been prominent in the two-phase ({gamma} + {alpha}{sub 2}) alloys: a lamellar structure consisting of lamellar colonies containing alternating {gamma} and {alpha}{sub 2} grains. In general, duplex structures display better elongation and strength, whereas lamellar structures show better toughness and fatigue crack-growth resistance. However, a problem with both microstructures, as with most intermetallics, is that fatigue-crack growth rates, da/dN, show a very strong dependence upon the applied stress-intensity range, {Delta}K, i.e., da/dN {proportional_to} {Delta}K{sup m}, where m is greater than {approximately}10. Small cracks (typically < {approximately}500 {micro}m in length) are known to grow at applied {Delta}K below the long crack threshold, and to exhibit growth rates in excess of those corresponding to long cracks (typically larger than 2--3 mm) at the same applied {Delta}K levels. Accordingly, the objective of the present study is to examine the small-crack effect in a commercial {gamma}-based TiAl alloy by comparing the growth-rate behavior of long (through-thickness) cracks with that of small surface cracks for both duplex and fully lamellar microstructures.
- Sponsoring Organization:
- Department of the Air Force, Washington, DC (United States)
- OSTI ID:
- 540929
- Journal Information:
- Scripta Materialia, Vol. 37, Issue 5; Other Information: PBD: 1 Sep 1997
- Country of Publication:
- United States
- Language:
- English
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