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 690-732°C 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 γ matrix and γ′ 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 γ matrix and γ′ precipitates on consecutive close packed {111} glide planes.