Misorientation effect of grain boundary on the formation of discontinuous precipitation in second and third generation single crystal superalloys

Abstract

[001] tilt artificial grain boundaries of Ni-based single crystal superalloys CMSX-4 and DD10 have been prepared by self-diffusion bonding. The microstructural stability of 0 ∼ 30° artificial grain boundaries have been investigated after heat treatment at 1100 °C for 0 ∼ 300 h. TCP phases and cellular colony developed on boundaries are related to misorientation angle of the bonded boundaries of DD10 and DD10 alloys as well as the bonded boundaries of CMSX-4 and DD10 alloys. The heterogeneous nucleation of TCP phase, enveloped by γ′ film, occurred along 15° and 20° boundaries. Discontinuous Precipitation (DP) reaction occurred along high misorientation angle (20°∼ 30°) boundaries. However, no TCP phase formation existed along grain boundaries with different misorientation angles in CMSX-4/CMSX-4 bonded alloys as well as for a 0° boundary in DD10/DD10 and CMSX-4/DD10 bonded alloys. The current study clearly suggests that grain boundary precipitation and its morphology were influenced by the misorientation angle of grain boundary and the content of refractory elements in alloy. © 2014 Owned by the authors, published by EDP Sciences.