High temperature tensile behavior of a thin-walled Ni based single-crystal superalloy with cooling hole: In-situ experiment and finite element calculation

Abstract

The high temperature tensile behavior for film-hole plates of a Ni based single-crystal superalloy has been investigated. Both the hole and the drill-produced recast layer are detrimental to tensile properties. During yielding, the strain distribution obtained in-situ by digital image correlation technique exhibits an X-like concentration at <101> directions around the hole. The crack initiates on the hole's edge with different crystallographic directions, depending on the recast layer. The fracture mechanism for 980 °C tensile exhibits a necking-dimple process, where plastic deformation is originated from the a/2 [101](11¯1¯) dislocation's by-passing. The Peierls-Nabarro force on [101](11¯1¯) slip system is 258.7 MPa, leading to the yielding of plate-type specimen. The finite-element method results indicate an X-like concentration of the resolved shear stress for such slip system around the hole, where the stress exceeds the Peierls-Nabarro force. This results in an X-like plastic deformation during yield, which explains the in-situ experimental results. The different chemical compositions and phase structures result in the softer nature of recast layer and the special stress/strain concentrated in it. The crack initiation and propagation around the hole also investigated in detail, via combining the experimental and computational results.