No abstract

No abstract

The fatigue crack propagation (FCP) behaviour of < 001 > axially oriented single edge notch (SEN) tension specimens (R = 0.05) if CMSX-2 has been examined. At 950°C c 100 > oriented cracks propagate faster than < 110> oriented cracks in the (001) plane.The influence of y I morphology on FCP at 750 and 950°C has been determined. Increasing the test temperature from 750 to 950°C lowers the FCP rates especially of the standard heat treated (ST) material (cuboidal y I).FCP rates of the thermomechanicaly treated (TMT) material, which has a raft-like y 1 and which simulates the microstructure formed after short high temperature service, are not very sensitive to temperature variations between 750 and 950°C. Higher FCP rates at 950°C for the TMT compared to the ST material have been related to fracture morphology. Time dependent FCP mechanisms were explored at 950°C for cuboidal and raft-like y I materials by performing continuous cycle (triangular wave form) and hold time tests. Hold time tests exhibited lower FCP rates. Tests in air had much slower FCP rates than tests in vacuum at low AK, especially with hold times. Repeatedly changing the environment from vacuum to air and vice versa, at 950°C with hold time provides confirmation of the slower propagation rates in air than in vacuum. Oxide-induced closure at the crack tip can explain the drastic environmental effect on FCP rates at low AK values while creep mechanisms can explain the acceleration at high AK when hold time is added in vacuum.

No abstract

No abstract