The effects of boron addition on the microstructure and mechanical properties of Co-Re-based high-temperature alloys

  High-melting-point Co-Re-base alloys show promise as a new class of high-temperature material. However, polycrystalline alloys fracture intergranularly. The addition of boron changes the fracture mode and dramatically improves the strength and ductility. Cr2B-type borides form at grain boundaries even with 200 ppm B addition in a Co-17Re-23Cr alloy. Borides are not, however, present at all grain boundaries, and electron energy loss spectroscopy could not detect elemental B segregation at grain boundaries. Measurements of boron mapping by neutron-induced radiography indicates that segregation of B to grain boundaries occurs, though only in some Co-Re alloy compositions.