Effect of boron on lamellar grain refinement and lath formation in wrought processed gamma TiAl alloys

Effects of boron additions (0-0.5 at%) are discussed in wrought processed fully lamellar microstructures of TiAl-base alloys. Boron additions greater than 0.03at% produce borides present (often in the ribbon forms) in interdendritic, regions. Hot working (forging or extrusion) breaks up and redistributes these borides into arrays of flake-like borides that effectively retard the high-temperature alpha-grain growth through the GB pinning process. For the given forging reduction, the resulting lamellar grain sizes for each alloy set are quantitatively related to the boron content. The borides on alpha grain boundaries help the gamma phase nucleate to raise the lamellar formation temperatures, leading to the formation of coarser and more inhomogeneous lath structures.