TY - GEN
T1 - Fatigue-Crack Propagation in Gamma-Based Titanium Aluminide Alloys at Large and Small Crack Sizes
AU - Kruzic, J. J.
AU - Campbell, J. P.
AU - Ritchie, R. O.
PY - 1998/11
Y1 - 1998/11
N2 - Most evaluations of the fracture and fatigue-crack propagation properties of 7+ Oj titanium aluminide alloys to date have been performed using standard "large-crack" samples, e. g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i. e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller (<500 [im) and where the small-crack fatigue threshold may be the most relevant design parameter. In this study, we compare and contrast the cyclic crack-growth behavior of both large (a > 5 mm) and small (c - 25-300 Um) cracks in a y-TiAl based alloy, of composition Ti-47Al-2Nb-2Cr-0. 2B (at. %), specifically for duplex (average grain size -17 jim) and refined lamellar (average colony size -150 (im) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i. e., crack bridging) contributions to cyclic crack advance. © 1999 Materials Research Society.
AB - Most evaluations of the fracture and fatigue-crack propagation properties of 7+ Oj titanium aluminide alloys to date have been performed using standard "large-crack" samples, e. g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i. e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller (<500 [im) and where the small-crack fatigue threshold may be the most relevant design parameter. In this study, we compare and contrast the cyclic crack-growth behavior of both large (a > 5 mm) and small (c - 25-300 Um) cracks in a y-TiAl based alloy, of composition Ti-47Al-2Nb-2Cr-0. 2B (at. %), specifically for duplex (average grain size -17 jim) and refined lamellar (average colony size -150 (im) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i. e., crack bridging) contributions to cyclic crack advance. © 1999 Materials Research Society.
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U2 - 10.1557/proc-552-kk2.3.1
DO - 10.1557/proc-552-kk2.3.1
M3 - RGC 32 - Refereed conference paper (with host publication)
VL - 552
T3 - Materials Research Society Symposium - Proceedings
BT - Proceedings of MRS Meetings
PB - Cambridge University Press
T2 - 1998 MRS Fall Meeting
Y2 - 30 November 1998 through 3 December 1998
ER -