Tensile behaviour of different pretreated alloy 718 sheets welded with electron beam welding (EBW)

Abstract

The present paper investigates the tensile behaviour of alloy 718 sheets processed after electron beam welding (EBW). The alloy 718 sheets were pretreated in three conditions: as received, solution and precipitation pretreatments. Metallographic and fractographic examination on the specimens were conducted with optical microscope, scanning and transmission electron microscopes. Experimental results show that cracks propagate through all of the fusion zones during tensile test. The intermetallic laves phase, which precipitates along the fine columnar grain boundary in the fusion zone, offers a preferred crack propagation path, especially for the precipitation pretreated weld. The static ductility of precipitation-treated weld decreases significantly after EBW. This was attributed to high precipitation density of laves phase along the columnar grain boundary. Relatively high tensile strength and ductility of as-received and solution-pretreated welds can be obtained by using two sequential welding passes. The first pass is full penetration welding with high heat input, and the secondary pass uses cosmetic welding to reduce the surface undercut resulted from the first pass.

Aging response of transient liquid phase bonded wrought IN718 superalloy: influence of post-bond heat treatment

“…Aging behavior of the joints is influenced by the chemical composition/microstructure gradient across the bond region. For instance, it has been reported 5–7 that the formation of Lave phase, (Ni,Fe) 2 Nb, in fusion zone ties up the Nb, the key alloying element determining the strengthening role in both γ ″ and γ ′, and hence depletes the principal alloying element required for hardening from the matrix resulting in weak aging response of fusion zone compared to the base metal. In standard TLP models, combining isothermal solidification with a subsequent solid state homogenisation treatment, offers the possibility of producing ideal joints with homogenous chemical composition and microstructure across the bond region.…”