Effect of Boron Addition on the Microstructure and Mechanical Property of Cobalt-Based Haynes 188 Alloy

Abstract

The cobalt-based superalloys are required for high-temperature components depending on solid-solution strengthened effect. While the microstructure and mechanical properties stability are also brought about by the grain boundaries cohesion and strength. Therefore, the role of boron on the microstructure and the stress rupture properties of cobalt-based Haynes 188 superalloy were studied. Here, we found that boron co-segregation with carbon mainly distributes in the M23C6 and M6C carbides and facilitates the formation of M23C6 carbide in hot rolling condition. Borides precipitate along the grain boundaries during solution treatment and have coherency relationship with the matrix due to boron diffusion and segregation, and minor boron addition also delays the dissolution of the secondary precipitation of M6C carbides, as compared to no precipitations in the 0B alloy. Borides serves as strong obstacle to the migration of grain boundaries and restricts the nucleation and growth of dynamic recrystallization, which profited from the suppression of linkage and propagation of micro-cracks, substantially improving the stress rupture life and the ductility.

Keywords: Haynes 188 alloy, Boron, Borides, stress rupture properties