Effect of Skew Angle of Holes on the Thermal Fatigue Behavior of a Ni-based Single Crystal Superalloy

In the present work, holes of various skew angles were electrochemically machined in the middle of the plate specimens in a Ni-based single crystal superalloy and crack initiation and propagation around holes during thermal fatigue cycles (20–1100 °C) were investigated. It was demonstrated that the skew angles had a significant effect on the initiation and propagation of thermal fatigue cracks. During thermal fatigue process, stress concentration occurred at the edge of the holes. As for skew angles, the maximum stress concentration appeared at the acute side of holes. The maximum stress concentration resulted in plastic deformation at the acute side of the 30° hole, driving the thermal fatigue cracks to initiate after 220 cycles and propagate along [01¯1]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$[0\bar{1}1]$$\end{document} direction. However, the stresses concentrated at the edge of 90° or 60° holes were not large enough to initiate cracks even after 580 thermal cycles. This work will help to understand the local deformation behavior in the vicinity of cooling holes with various skew angles and have serious design implications for turbine blades.