Influence of grain boundary precipitation and segregation on cracking of cast and wrought superalloys containing B and Zr
Felix Theska, R. Buerstmayr, H. Liu, M. Lison-Pick, Steven R. Street, Sophie Primig
Abstract
Improving the hot workability of cast and wrought Ni-base superalloys is complex due to grain boundary cracking. Mitigation approaches focus on grain boundary active microalloying elements B and Zr. René 41 is one of few superalloys with exceptional high-temperature strength required for next-generation aircraft engine components. Its grain boundaries are decorated by solutes and γ', carbide, and/or boride precipitates. However, the detailed influence of B & Zr additions on the hot workability and grain boundary decoration of superalloys like René 41 remain unexplored. To address this knowledge gap, we industrially manufactured two René 41 variants, a nominal and a high B & Zr one. Correlative microscopy reveals γ' and M2B grain boundary precipitation as supported by thermo-kinetic modeling. Site-specific atom probe microscopy reveals the interfacial excess close to those grain boundaries most prone to cracking. In the nominal variant, γ'/γ interfaces are less decorated by B, C and Zr with 4.6 atoms nm−2. γ/γ interfaces are saturated at ~ 5.8 atoms nm−2 in both variants. Grain boundary pinning of M2B is increased by Zr promoting γ' precipitation, causing grain boundary cracking. Optimized solute concentrations are proposed. Based on our findings the next iteration of superalloy design using microalloying is enabled.