On the fatigue small crack behaviors of directionally solidified superalloy DZ4 by in situ SEM observations

Small fatigue crack behaviors in a nickel-based directionally solidified superalloy DZ4 were studied by in situ Scanning Electron Microscopy. The crack initiation and propagation manners were identified under different temperatures, i.e. 25 degrees C, 350 degrees C, 700 degrees C. Fatigue crack growth occurred preferentially along slip bands at 25 degrees C and 350 degrees C but by Mode-I type at 700 degrees C. The crack growth rate generally increased with temperature, especially between room temperature and 350 degrees C. The anomalous small crack growth was analyzed by in situ examining the effect of microstructure. The small cracks were found to be primarily microstructurally small and secondly mechanically small. (C) 2010 Elsevier Ltd. All rights reserved.