Research on laser welding of cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft

Abstract

Exploratory experiments of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energydispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. The corresponding mechanisms were discussed in detail. Results showed that the laser-welded seam had non-equilibrium solidified microstructures consisting of FeCr 0.29 Ni 0.16 C 0.06 austenite solid solution dendrites as the dominant and some fine and dispersed Ni 3 Al ␥ phase and Laves particles as well as little amount of MC short stick or particle-like carbides distributed in the interdendritic regions. The average microhardness of the welded seam was relatively uniform and lower than that of the base metal due to partial dissolution and suppression of the strengthening phase ␥ to some extent. About 88.5% tensile strength of the base metal was achieved in the welded joint because of a non-full penetration welding and the fracture mechanism was a mixture of ductility and brittleness. The existence of some Laves particles in the welded seam also facilitated the initiation and propagation of the microcracks and microvoids and hence, the detrimental effects of the tensile strength of the welded joint. The present results stimulate further investigation on this field.

Transmission electron microscopy characterization of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft

“…Flow of high purity argon gas was passed through the molten pool from both top and lateral sides to provide a protective environment for the sake of avoiding the reaction between the molten metals and ambient air. Further details on laser welding and sample preparation procedures can be found in our previous work [13].…”

“…In this study, thin foils were prepared by cutting slices (0.15 mm thick) from the central typical region of the solidified fusion zone from the welded joint based on our previous OM and SEM observations [13], by electric discharging machine. The slices were first ground mechanically to less than 50 m. Discs of 3 mm diameter were punched mechanically and then dimpled by means of a Gatan Model 656 Dimple Grinder.…”

“…1. Morphology of the laser weld between cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft [13].…”

“…In our recent related studies [13,14], laser welding K418 turbo disk and 42CrMo shaft were conducted. Attempts to characterize the microstructure of the phases present in the seam zone were made on X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS).…”

“…However, there still exist three problems, the first is that it is usually hard to exactly identify and clearly marked the Ni 3 Al (␥ ) phase due to the relatively small amount and the superposed distribution with Laves phase and MC carbides although the XRD results indicate its existence. The second is Laves phase is heavily alloyed with multiple elements and its form is very complex, no present JCPDS cards could be found to identify the exact existence of it as mentioned in [13]. The third is that according to JCPDS standard data, interplanar spacing corresponding to diffraction peaks of possible phases in the fusion zone is close to each other, and the strong reflections of these phases are almost superimposed on one another.…”