Search

[Display omitted] • Inconel 718 and Nimonic 80A were welded using rotary friction welding. • Welded joints showed lesser toughness than the base metals. • Post-weld heat-treated welded joints showed improved crack growth resistance. • Crack grew along weld zone with no deviation to either of the base metals. • Fractography of weldments confirmed linear elastic fracture mechanics. In this paper, fracture toughness (FT) and fatigue crack growth rate (FCGR) studies were carried out on dissimilar metal welded joints (DMWJs) of Inconel 718 and Nimonic 80A. The DMWJs were made using rotary friction welding (RFW). The base metals (BMs) showed plastic mismatch. Single edge notched bend specimen was used for FT and FCGR studies. The crack was initiated and propagated along the weld. BMs showed higher toughness than the DMWJs. The crack growth resistance offered by the DMWJs were inferior to BMs. Post-weld heat-treated DMWJ showed improved FT and crack growth resistance than the untreated DMWJ. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates fracture toughness and fatigue crack growth behaviour of mode-I cracked bi-metallic compact tension specimens. The specimens were made of weak-copper (UNSC11000) and strong-alloy steel (En31) arc-welded with nickel-filler. Residual stresses induced in constituent materials during welding, due to their different coefficients of thermal expansion (thermal mismatch) were measured at important locations in all the materials near the weld zone. Several notched specimens with positions of crack tip in critical zones of copper, steel and nickel-weld were subjected to fracture tests. The specimens were fatigue precracked prior to fracture testing. Bi-metallic specimens having an equal initial crack length were subjected to constant-amplitude fatigue crack growth rate tests until their fracture occurred. Residual stress intensity factor as a function of crack length was computed theoretically for inclusion in the analysis. Thermal and mechanical mismatches between constituent materials, the latter represented by elastic and plastic property differences, were strongly found to affect the behaviour of crack tip in the vicinity of the weld under both monotonic and fatigue load. The combined effect of “elastic–plastic mismatch” across the material interfaces over the crack tip was described by crack driving force, J interface . Under monotonic load (i) fracture toughness of bi-metallic specimens with crack in copper side facing the weld backed by steel was found to be higher than that of monolithic copper with crack arrest noticed in all the specimens when the crack tip was near the weld. Furthermore, J interface was found to be positive in this case which implied that the crack driving force, J tip , was less than the remotely applied crack-driving force, J applied . (ii) Fracture toughness of bi-metallic specimens with crack in steel side facing the weld backed by copper was found to be lesser than that of monolithic steel with the specimens failing quickly in the form of short brittle fracture within steel and the part of the weld. In addition, J interface was negative in this case with J tip being more than J applied . Under constant amplitude fatigue load (i) for crack growth from copper to steel side, crack growth rates in copper side retarded in the vicinity of the weld due to shielding caused by the stronger weld and back up steel. The crack deflected away from mode-I plane before penetrating into weld and back up steel. (ii) For crack growth from steel to copper side, crack growth rates in steel accelerated in the vicinity of the weld due to the amplification caused by the “elastic–plastic” property gradient from higher to lower. Furthermore, the crack penetrated through the weld and back up copper with no deflection. The results were also compared with those of monolithic metals subjected to similar fracture and fatigue crack growth rate tests. The shielding and amplification trends in the fatigue crack growth tests were not found to be altered by residual stresses. This implied that the combined effect of “elastic–plastic” mismatch was dominant over that of residual stresses in both directions of crack-transition. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents metallurgical and mechanical examinations of joints between dissimilar metals viz. copper (UNSC11000) and alloy steel (En31) obtained by Shielded Metal Arc Welding (SMAW) using two different filler materials, bronze and nickel-base super alloy. The weld bead of the joint with bronze-filler displayed porosity, while that with nickel-filler did not. In tension tests, the weldments with bronze-filler fractured in the centre of the weld, while those with nickel-filler fractured in the heat affected zone (HAZ) of copper. Since the latter exhibited higher strength than the former, all the major tests were undertaken over the joints with nickel-filler alone. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) indicated corrugated weld interfaces and favorable elemental diffusions across them. X-ray diffraction (XRD) studies around the weld interfaces did not reveal any detrimental intermetallic compounds. Transverse bending tests showed that flexural strengths of the weldments were higher than the tensile strengths. Transverse side bend tests confirmed good ductility of the joints. Shear strength of the weld-interface (Cu–Ni or Ni–steel) was higher than the yield strength of weaker metal. Microhardness and Charpy impact values were measured at all the important zones across the weldment. [Copyright &y& Elsevier]