Surface microstructure modification of hypereutectic Nb-Si based alloys to improve oxidation resistance without damaging fracture toughness

To achieve a good balance between oxidation resistance and fracture toughness of hypereutectic Nb-Si based alloys, we tune the alloy surface microstructure by an approach of rapid surface remelting. The remelted layer with a refined and modified hypereutectic microstructure is created on a bulk cast Nb-20Si-24Ti-2Cr-2Al (at.%) alloy via electron beam surface melting (EBSM). The EBSM-remelted layer markedly improves the oxidation resistance of the experimental alloy, showing a decreased parabolic rate constant and a reduced weight gain upon oxidation at 1250 °C. Three-point bending tests show that fracture toughness of the EBSM-treated alloy is comparable to that of the cast alloy without EBSM treatment. This work thus demonstrates the capability of surface microstructure modification enabled by rapid remelting for improving the oxidation resistance of Nb-Si based alloys while maintaining the fracture toughness.