Co-precipitation of M2B on ZrO2 in a Ni-base superalloy with B & Zr additions

Abstract

Polycrystalline superalloys are high-performance materials with complex microstructures often affected by micro-alloying elements B, C, or Zr added to control mechanical properties during manufacturing and in-service. This requires precise compositional control and makes increasing recycling rates challenging. One example is Zr in scrap used for making René 41. Zr is incorporated due to comparably higher concentration in Waspaloy commonly mixed with René 41 scrap. Increasing recycling rates therefore requires a detailed understanding of the impact of Zr on the microstructure of superalloys. High B and High B&Zr variants of the Ni-based superalloy René 41 are compared using analytical electron microscopy, focused ion beam, and transmission electron microscopy techniques. We show that morphology and dispersion of C16-M2B borides are affected by Zr. C16-M2B, TiC, (Ti,Zr)C, and γ′ Ni3(Al,Ti) co-precipitate on m-ZrO2. The lattice mismatch between C16-M2B and m-ZrO2 is mitigated with an (012)ZrO2 || (200)M2B orientation relationship allowing epitaxial growth. This demonstrates how the C16-M2B morphology and dispersion is affected by Zr additions in polycrystalline superalloys.