In situ TEM investigation on the precipitation behavior of μ phase in Ni-base single crystal superalloys

The precipitation behavior of phase in Ni-base single crystal superalloys was investigated by in situ transmission electron microscopy (TEM). A layer-by-layer growth process with a ledge propagation mechanism was first observed during in situ precipitation. Three types of mu phase with different morphologies were found, which grow along [001](mu) with (001)(mu) planar defects, [-111](mu) with (1-12)(mu) planar defects, as well as both directions with mixed planar defects. High-resolution TEM image and established atomic models reveal a basic growth mechanism of mu phase by stacking on (001)(mu) plane and randomly forming coherent planar defects, while the nucleation of incoherent (1-12)(mu) planar defects at the early stage of precipitation plays an important role in affecting the basic growth mechanism. The frequent faults during the stacking process of the sub-unit layers within mu lattice should be responsible for the defect formation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.