Evaluation of thermo-mechanical fatigue crack propagation behavior of Ni-based single crystal superalloy CMSX-4

Abstract

Out-of-phase thermo-mechanical-fatigue (TMF) crack propagation tests were performed under load control condition by using compact tension specimen made of Ni-based single crystal superalloy, CMSX-4, and the effect of temperature range during loading cycle on crack propagation behavior was studied. The tests were conducted in the temperature range of 200-500°C and 200-800°C. For comparison, isothermal fatigue crack propagation test at 200°C was additionally performed. In the specimens tested under 200°C isothermal and 200-500°C out-of-phase conditions, the fatigue cracks propagated on {111} slip planes. In the specimen tested under 200-800°C out-of-phase condition, the crack propagated on the plane normal to the loading axis independently of crystallographic orientation, when the applied ΔKI was lower than about 50 MPa･m0.5, in spite of the fact that the maximum tensile loading during cyclic loads was applied at 200°C. When ΔK was larger than about 50 MPa･m0.5, the crack propagated on {111} planes near the specimen side faces. These crack propagation rates in the specimens tested under 200-500°C out-of-phase and 200°C isothermal conditions could be evaluated by using the resolved shear stress intensity factor range. Crack propagation rate in the specimen tested under 200-800°C out-of phase could be evaluated by energy release rate for an anisotropy body. A reasonable interpretation was proposed on the transition of fracture mode between the sliding mode to opening mode, by an aid of the resolved shear stress intensity factor range.

Keywords

• single crystal superalloy
• slip plane crack propagation
• thermo mechanical fatigue
• transition of fracture mode