Deformation mechanisms and fatigue crack initiation in single crystal nickel superalloys

Despite high safety factors in the design of nickel superalloy components in gas turbine engines, part failure and material degradation still ultimately occur. Fatigue failure remains the most common cause of failure for these components, and exists in the forms of mechanical, thermomechanical and creep; cyclic stress and strain leads to localised plastic deformation at regions of high stress concentration, around complex geometries, pores, and inclusions, which results in the initiation of fatigue cracks. A greater understating of this process will lead to more accurate component lifing predictions, enabling safer operation and a reduction in cost.
Notched single crystal nickel samples have been tested under fatigue loading to determine fatigue life; using material data, along with crystal plasticity finite element (CPFE) modelling, complex models have been generated to estimate fatigue lives using damage criteria. Detailed models of the microstructure of these alloys have been created using representative volume elements (RVE) in order to extract slip strengths of different slip systems present in the gamma/gamma' microstructure, creating a two-phase representative model. These models will be used to simulate fatigue loading of notched single crystal samples to determine any for mechanistic drivers for fatigue crack initiation.