The effect of load ratio and grain size on fatigue crack growth rates in nickel base superalloy AP-1

Fatigue crack propagation rates have been investigated in the powder metallurgy formed nickel base superalloy AP-1. Fatigue crack growth data are presented for different microstructures and load ratio throughout the life history of the crack and discussed in terms of current theories of fatigue crack propagation. The experimental results indicate that threshold values for crack growth depends on load ratio and grain size. However, the effective threshold values are virtually not affected by these values and characteristics of materials tested