Near-threshold crack growth behavior of a single crystal Ni-base superalloy subjected to mixed-mode loading

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20000287

John, R; DeLuca, D; Nicholas, T; Porter, J

Ni-base single crystal superalloys, which are used in applications such as gas turbine engine blades, are primarily loaded along the (001) direction. Mode II (crystallographic shear) type cracking along the (111) plane is frequently the mode of growth in the early stages of fatigue failure of these components. Disks with a middle crack were used to characterize crystallographic shear crack growth from machined flaws oriented parallel to a (111) plane of a single crystal alloy. Automated crack growth experiments were conducted at constant stress ratio in the near threshold regime. Various combinations of Mode I and Mode II loading were achieved by orienting the machined flaw at different angles ({theta}) to the loading axis. Loading angle {theta} = 0{degree} (pure Mode I loading) resulted in crystallographic crack extension along alternating (111) slip systems producing a zig-zag pattern. This orientation exhibited significant resistance to self-similar crack growth from the machined flaw. In contrast, self-similar crack growth was achieved with relative ease for loading angles, {theta} {ne} 0{degree} (mixed mode). In the mixed mode tests with K{sub 1} > 0, the crack growth rate was 10 to 50 times higher than that under Mode I loading. Preliminary results indicate that crack growth is non-crystallographic at 593 C.

• Research Organization: Air Force Research Lab., Wright-Patterson AFB, OH (US)
• OSTI ID: 20000287
• Report Number(s): CONF-9805206--; ISBN 0-8031-2602-6
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
36 MATERIALS SCIENCE
CRACK PROPAGATION
FATIGUE
FRACTURE MECHANICS
GAS TURBINES
HEAT RESISTING ALLOYS
MICROSTRUCTURE
NICKEL BASE ALLOYS
TURBINE BLADES