A TEM study of creep deformation mechanisms in ALLVAC 718Plus

A preliminary study on the evolution of creep deformation substructure in Ni-base superalloy Allvac 718Plus has been performed. Specimens crept at 620 MPa and at temperatures ranging from 690-732ºC were examined utilizing diffraction contrast TEM characterization techniques. Creep was interrupted at 1-2.5% strain in order to study the deformation substructure following a limited amount of deformation. The dominant deformation modes at each of the test temperatures were highly planar in nature and involved shearing of the y matrix and y' precipitates on {111} glide planes. In addition, paired a/2<110> dislocations were evident which suggest an antiphase boundary shearing mechanism. Creep induced microtwinning was also observed at the highest creep temperature which was created by identical a/6<112> Shockley partial dislocations that shear the y matrix and y' precipitates on consecutive close packed {111} glide planes. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.