Abstract
This research work focuses on the mechanical behaviour comparative assessment in conjunction with microstructural evolution characterization of Waspaloy® and Inconel® 718, following TIG and EB welding. Both of the forth-mentioned alloys are precipitation strengthened Ni-based superalloys, widely used in chemical, petrochemical and aerospace industries. More specifically, Waspaloy® is strengthened by the precipitation of the ordered fcc gamma prime intermetallic phase, γ΄ - Ni3(Al,Ti), while Inconel® 718 is mainly hardened by the ordered bct gamma double prime phase, γ΄΄ - Ni3Nb, in addition to γ΄. After both welding processes, samples of the above superalloys were subjected to appropriate post-weld heat treatment, according to SAE Aerospace Material Specifications. The mechanical response of the tested specimens is assessed via uniaxial tensile tests, combined with fractography. Furthermore, the microstructural characterization of TIG and EB welds is conducted by Scanning Electron Microscopy (SEM), coupled with Energy Dispersive Spectroscopy (EDS), while phase identification was performed through X-Ray Diffraction (XRD). The main objective of the present research work is to examine the influence of post-weld heat treatment on the Waspaloy® and Inconel® EBW and TIG welds microstructural evolution features, correlating them with their corresponding mechanical behaviour.
Highlights
Waspaloy is strengthened by the precipitation of the intermetallic gamma prime phase γ (Ni3(Al,Ti)) and MC, M6C και M23C6 carbides, while Inconel 718 is mainly strengthened by gamma double prime phase γ (Ni,Co)3(Nb,Ta,Ti,Al), in addition to γand corresponding carbides
Waspaloy presents some limitations related to its weldability due to its susceptibility to strain age cracking under conditions of heavy restraint and requires special as well as controlled welding conditions [1, 2]
The post-weld heat treatment required for Waspaloy to enhance mechanical strength and eliminate internal stresses consists of three stages, namely homogenization, stabilization and ageing [1, 2]
Summary
Waspaloy is strengthened by the precipitation of the intermetallic gamma prime phase γ (Ni3(Al,Ti)) and MC, M6C και M23C6 carbides, while Inconel 718 is mainly strengthened by gamma double prime phase γ ́ (Ni,Co)3(Nb,Ta,Ti,Al), in addition to γand corresponding carbides. Waspaloy presents some limitations related to its weldability due to its susceptibility to strain age cracking under conditions of heavy restraint and requires special as well as controlled welding conditions [1, 2]. The most widely-used welding process is Tungsten Inert Gas (TIG), a welding technique that uses a non-consumable tungsten electrode. Waspaloy is susceptible to welding solidification cracking and during post-weld heat treatment (strain-age cracking). The post-weld heat treatment required for Waspaloy to enhance mechanical strength and eliminate internal stresses consists of three stages, namely homogenization, stabilization and ageing [1, 2]. Electron Beam Welding (EBW) is a non-conventional, highly automated and precise technique; suitable for joining materials that are not weldable (i.e., Waspaloy) [1, 2]
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