Experimental studies of fracture and fatigue crack growth in dissimilar metal welded joints of nickel-based superalloys: Cracks oriented along the weld

Abstract

Nickel-based superalloys, Inconel 718 and Nimonic 80A, were welded without any interlayer for Blisk manufacturing in aerospace industries. Fracture toughness and fatigue crack growth rate of the dissimilar metal welded joints were experimentally studied to confirm their structural integrity. Cracks were oriented in and along the weld. Base metals, Inconel 718, and Nimonic 80A differ in yield strength but have the same modulus of elasticity. Electron beam welding was used to butt weld Inconel 718 to Nimonic 80A. J resistance curve (J vs. crack extension) was experimentally found to determine the elastic–plastic fracture toughness. The welded specimens showed lesser fracture toughness and higher crack growth rates than base metals. An increase in load ratio resulted in an increase in fatigue crack growth rate in the high ΔK region and a decrease in ΔK_th. Fractography studies confirmed linear elastic and plane strain fracture all along the fatigue crack growth rate path except for the final fracture with plane stress.