Influence of Hf contents on interactions between Nb-silicide based alloys and yttria moulds during directional solidification

► In the alloys contained Hf, a reaction layer was formed and inclusions were dispersed. ► In the alloy without Hf, there was no apparent reaction layer or visible inclusion. ► The decrement of Hf caused the weakened interactions and reduced contaminations. ► Yttria is a promising suitable refractory material, especially for the alloys without Hf.