High-temperature fatigue-crack growth behavior in a two-phase ({gamma} + {alpha}{sub 2}) TiAl intermetallic alloy
- Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering
- UES, Inc., Dayton, OH (United States). Materials and Processing Division
From an experimental study on the high temperature fatigue-crack growth behavior in a two-phase ({alpha}{sub 2} + {gamma}) Ti-47.3Al-2.3Nb-1.5Cr-0.4V alloy, processed in fine duplex and coarse lamellar microstructures, the following conclusions may be made: Fatigue-crack growth resistance of the alloy, both in the lamellar and duplex microstructures, is found to be optimal at 800 C and compromised at 650 C compared to behavior at room temperature. While faster growth rates at 650 C are presumably associated with higher crack opening displacements at elevated temperatures, the slower growth rates at 800 C may be attributed primarily to a large increase in ductility leading to crack-tip blunting above the ductile-to-brittle transition temperature. Improved damage tolerance is apparent, especially in the duplex microstructure, at 650 and 800 C from the shallower slope on the da/dN-{Delta}K curve. At all temperatures, the lamellar microstructure exhibits superior fatigue-crack growth resistance compared to the duplex structure, primarily due to beneficial extrinsic effects from crack deflection, microcracking ahead of the crack tip and resultant shear-ligament bridging by microlaminate colonies in the wake. Fatigue thresholds in lamellar {gamma}-TiAl range between {approximately}8--13 MPa{radical}m; corresponding values for the duplex alloy are {approximately}5.5--8MPa{radical}m.
- OSTI ID:
- 103598
- Journal Information:
- Scripta Metallurgica et Materialia, Vol. 33, Issue 3; Other Information: PBD: 1 Aug 1995
- Country of Publication:
- United States
- Language:
- English
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