Effects of vacuum on gas content, oxide inclusions and mechanical properties of Ni-based superalloy using electron beam button and synchrotron diffraction

Abstract

The effects of vacuum induction melting (VIM) vacuum (<1 Pa–100 Pa) on gas content, oxide inclusions and mechanical properties of Ni-based superalloy K4648 has been investigated by electron beam (EB) button experiment under high vacuum (10-3 Pa) and high resolution synchrotron X-ray powder diffraction (SXPD). The results indicated that VIM remelting vacuum drop has obvious effect on the existing form of trace oxygen. The total amount of oxygen did not increase significantly but a dramatic increase in the amount of oxide inclusions by 1–2 orders of magnitude was found. The inclusions are mainly oxides including Al2O3, Cr2O3, NiAl2O4 and complex oxides or sulfides. Remelting under 100–110 Pa has no significant effect on mechanical properties such as stress rupture life and tensile strength but decreased ductility obviously. In comparison to the normal vacuum counterpart, the tensile elongation and impact ductility of the alloy remelted under lower vacuum level decreased by 67% and 39%, respectively. This study reveals the relationship between the vacuum level and mechanical properties of superalloys and highlights the trace amount of oxide inclusions which should be considered as one of the key issues for the cleanliness of virgin or revert superalloys apart from the typical measurement of the gas content only.

Keywords

• Superalloy K4648
• Electron beam (EB) button
• Synchrotron X-ray powder diffraction (SXPD)
• Oxygen content
• Ductility
• Inclusion