Effect of boron additions on the microstructure and transverse properties of a directionally solidified superalloy

The effect of boron additions ranging from 5 to 210 ppm on the microstructure and transverse properties of a directionally solidified (DS) superalloy was studied. Lamellar borides were observed in the as-cast specimens when B addition was increased to 210 ppm. The borides gradually decomposed during solution heat treatment. γ′ envelope formed around carbides in B containing alloys after solution heat treatment. No secondary carbides were found during the formation of the γ′ envelope. The transverse creep lifetime and the tensile properties at both room temperature and 870 °C were significantly improved when boron was added. However, further increasing in B content showed different effect on creep strength and tensile properties at different experimental conditions.