Directional and single-crystal solidification of Ni-base superalloys: Part II. Coincidence site lattice character of grain boundaries

Abstract

The development of grain boundary misorientations with an evolving axial texture during directional solidification has been examined using the electron backscattered diffraction (EBSD) technique on the Ni-base superalloys, CMSX4 and CM186LC. A preferred grain boundary misorientation distribution (GBMD) for a sharp 〈001〉 axial texture in CM186LC was associated with a clustering of misorientation axes (MAx) in the proximity of 〈001〉. This is accompanied by an enhanced distribution of coincidence site lattice (CSL) boundaries. The increased distribution of low angle boundaries, Σ1 and Σ5, can be attributed to the existence of a preferred MAx and accommodation by secondary intrinsic grain boundary dislocations. The more diffuse 〈001〉 axial texture in CMSX4 is associated with a significant proportion of MAx deviating from 〈001〉 and a dramatic reduction in the proportion of CSL boundaries.