On the role of Zr and B addition on solidification cracking of IN738LC produced by laser powder bed fusion

Abstract

The demand for manufacturing increasingly complex geometries for high temperature applications drives the increasing interest into additive manufacturing of nickel-based superalloys. Of particular interest are superalloys with high contents of the strengthening phase γ' such as IN738LC. Previous research suggests that especially B and Zr have a detrimental influence on crack formation during the laser powder bed fusion (LPBF) process. The present study investigates solidification cracks in an IN738LC derivative with increased B (0.03 wt.%) and Zr (0.07 wt.%) in more detail using high resolution techniques such as transmission electron microscopy (TEM) and atom probe tomography (APT). Analysis of the bulk material shows a high number of MC carbides containing Ti and Cr. The concentration profiles indicate non-equilibrium carbide compositions by suggesting that Cr is pushed out of these particles. The carbides are surrounded by a thin B-rich layer at the metal/carbide interface. Analysis of the fracture surface shows both Zr and small amounts of B in the formed oxide layer. The presence of these elements together with thermodynamic calculations and previously reported findings of the same material variant support the hypothesis that low-melting phases are likely reasons for cracking of IN738LC.