Role of yttrium in the microstructure and mechanical properties of a boron-modified nickel-based superalloy

The stress-rupture life of a nickel-based superalloy increases with increasing yttrium addition up to 0.013% Y, then decreases. The carbide morphology changes from continuous platelets to discrete blocks. Eutectic volume increases with increasing yttrium concentration. This results in the drop of rupture life when excess yttrium doped.