Review of Microstructure–Mechanical Property Relationships in Cast and Wrought Ni-Based Superalloys with Boron, Carbon, and Zirconium Microalloying Additions

Abstract

Cast and wrought Ni-based superalloys are materials of choice for harsh high-temperature environments of aircraft engines and gas turbines. Their compositional complexity requires sophisticated thermo-mechanical processing. A typical microstructure consists of a polycrystalline γ-matrix, strengthening Ni₃(Al,Ti) γ′ precipitates, carbides (MC, M₆C, and M₂₃C₆), borides (M₂B, M₃B₂, and M₅B₃), and other inclusions. Microalloying additions of B, C, and Zr commonly improve high-temperature strength and creep resistance, although excessive additions are detrimental. Grain boundary (GB) segregation may improve cohesion and displace embrittling impurities. Finely dispersed carbides and borides are desired to control grain size via GB pinning. However, excessive decoration of GBs may lead to failure during processing and in-service. Hence, a systematic review on the roles of B, C, and Zr in cast and wrought Ni-based superalloys is required. The current state of knowledge on GB segregation and precipitation is reviewed. Experimental and modeling results are compared across various processing steps. The impact of GB precipitation on mechanical properties is most well researched. Co-precipitation in proximity to GBs interacting with local microstructure evolution and mechanical properties remains less explored. Addressing these gaps in knowledge allows a more complete understanding of processing–microstructure–properties relationships in advanced cast and wrought Ni-based superalloys.