Numerical and experimental investigation of plasticity (slip) evolution in notched single crystal superalloy specimens

Single crystal nickel base superalloys (SCNBS) are being used increasingly for high temperature turbine blade and vane applications in aircraft and rocket engines. As a first step toward developing a mechanistically based fatigue life prediction system for SCNBS components, an understanding of the evolution of plasticity in regions of stress concentration, under the action of triaxial stresses, is necessary.; A detailed numerical and experimental investigation of the evolution of plasticity and slip sector boundaries near notches in SCNBS double-notched tensile specimens was conducted. The evolution of plasticity in the vicinity of notches in three specimens with a <100> loading orientation, and having their notches parallel to one of the <010>, <110> and <310> directions (secondary orientation), were studied. A three dimensional (3D) linear elastic anisotropic finite element model of the specimens was developed using ANSYS. Ni-base superalloys which deform by the shearing of the gamma' precipitate, were selected for the experimental study to insure that slip bands followed the slip planes, similar to single-phase materials. The tensile testing of the notched specimens was carried out using a 1125 Instron system, and optical microscopy was utilized to observe the slip bands on the surface of the specimens near notches. The experimental tests were conducted at room temperature to limit the plastic deformation to {lcub}111{rcub} planes, similar to FCC metals.; In this study, we demonstrate that a 3D linear elastic anisotropic finite element model is able to predict the activated slip planes and sector boundaries accurately on the surface of the specimens. The experimental and numerical results suggest that the dominant slip planes activated at low load levels persist even at high load levels, and the activation of other slip bands within a domain is initially inhibited. Results reveal that slip sector boundaries have complex curved shapes, rather than straight sector boundaries as predicted previously. Moreover, both the experimental and numerical results indicate that sector boundaries change with increasing load. A comparison between the isotropic and anisotropic results demonstrates that elastic anisotropy has a noticeable effect on the slip evolution near notches. (Abstract shortened by UMI.)...