Effect of boron addition on the microstructure and mechanical property of cobalt-based haynes 188 alloy

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 M 23 C 6 and M 6 C carbides and facilitates the formation of M 23 C 6 carbide in hot rolling condition. M 23 (B,C) 6 precipitates along the grain boundaries during solution treatment have coherency relationship with the matrix due to boron diffusion and segregation, which serve as strong obstacle to the migration of grain boundaries and restrict the nucleation and growth of dynamic recrystallization when stress rupture tests were conduct at 927 °C and 83 MPa. The lower volume fraction of DRX and the growth of carbides suppress the linkage and propagation of micro-cracks, substantially improving the stress rupture life and the ductility due to the addition of boron.