Effects of compositions and melting processes on the microstructure of multicomponent Nb-based super-high temperature alloys

Four batches of multicomponent Nb-based super-high temperature alloys with different compositions have been prepared by vacuum consumable arc-melting or vacuum non-consumable arc-melting. The effects of compositions and melting processes on the microstructure of multicomponent Nb-based super-high temperature alloys are studied. The results show that the four batches of alloys with different compositions are composed of the primary Nbss (Nb-based solid solution) dendrites, or the primary (Nb, x)₅Si₃ blocks and plates (x represents Ti, Hf and Cr elements) and the Nbss/(Nb, x)₅Si₃ eutectic clusters. With the increase of Si content, the amount of Nbss/(Nb, x)₅Si₃ eutectic clusters increases, and furthermore, the primary phase changes from the Nbss dendrites to the (Nb, x)₅Si₃ blocks and plates. The Nb silicides are in the forms of γ-(Nb, x)₅Si₃ and β-(Nb, x)₅Si₃. Some micro-cracks are observed in big Nb silicide blocks and plates for the four batches of alloy ingots.