Influence of carbon additions on microstructures and mechanical properties in additive manufactured superalloys

Abstract

Combined with scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and mechanical properties, the effects of three different carbon contents on mechanical structure–properties of nickel superalloys fabricated by laser metal deposition (LMD) were studied. The grains exhibited a preferred orientation and strong texture along the {001} plane. Meanwhile, it was confirmed that C exists in the form of MC and M₆C carbides in the C-containing alloys. Moreover, C addition reduced the residual stress but had little impact on microstructures. Additionally, the rupture life (760 °C/780 MPa) was remarkably improved as the C content was increased to 0.01 wt%. The improvement of stress rupture properties mainly contributed to the combined strengthening effect of MC and M₂₃C₆. However, with the excessive addition of C, the stress rupture properties were reduced significantly, as a high carbon content may cause stress concentration, making the material more prone to pore and crack formation under stress.