Analysis of fracture toughness and fatigue crack growth rates of electron beam-welded dissimilar nickel-based superalloys: Mode-I cracks oriented normal to the weld

Abstract

This paper discusses the experimentally obtained results of fracture toughness and fatigue crack growth rates of dissimilar metal-welded joints of Inconel 718 to Nimonic 80A. The dissimilar metal-welded joints were prepared in butt joint configuration using electron beam welding. Mode-I cracks were oriented normal to the weld. The base metals have different yield strength values (plastic mismatch) and ultimate tensile strength values but have the same elastic modulus and thermal expansion coefficients. The experiments were conducted using single-edge notched bend specimen design. The fracture toughness ( J) and fatigue crack growth rates of dissimilar metal-welded joints were affected by the direction of crack growth, such as cracks moving from stronger metal to weaker metal or vice versa. In comparison to Nimonic 80A (base metal), the J value of dissimilar metal-welded joint with crack direction from Nimonic 80A (stronger) to Inconel 718 (weaker) was lower. Moreover, the J value of dissimilar metal-welded joint was higher than that of Nimonic 80A (base metal) when crack traveled from Inconel 718 (weaker) to Nimonic 80A (stronger). In the fatigue crack growth rate test, the crack grew faster as it approached the weld interface from Nimonic 80A toward Inconel 718 due to crack acceleration. Conversely, the crack grew slowly in the opposite direction due to crack shielding. The onset of these effects began sooner for higher loads than lower loads.