Microstructure Evolution and Mechanical Properties of a Directionally Solidified Nb-Ti-Si-Cr-Al-Hf-Dy Alloy

Shenzhen Insititute, Peking University, Shenzhen 518057, China

^* Corresponding author: lysheng@yeah.net

Abstract

The Nb-Ti-Si-Cr-Al-Hf-Dy alloy was prepared by conventionally casting and then directionally solidified (DS) with the optical floating zone melting technology. Microstructural evolution and mechanical properties of the as cast (AC) and DS alloys were studied by XRD, SEM, TEM, compression and bending tests. The results exhibit that α-(Nb, Ti)₅Si₃, (Ti, Nb)₅Si₃ and (Nb, Ti)ss phases formed the microstructure of the AC alloy, with precipitates of Cr₂Nb, Dy₂O₃ and (Nb, Ti)₃Si along phase or grain boundaries. The DS alignes (Nb, Ti)ss and α-(Nb, Ti)₅Si₃ lamellae parallel to the growth direction and refines the eutectic cell, but coarsens the primary α-(Nb, Ti)₅Si₃ phase. The DS alloy exhibits strong orientation of (310)_{(Nb, Ti)5Si3} and (110)_{(Nb, Ti)ss} along the growth direction. TEM observation reveals that (Nb, Ti)ss and α-(Nb, Ti)₅Si₃ phases have an orientation relationship of [110]_{(Nb, Ti)ss} // [310]_{α-(Nb, Ti)5Si3} and (002)_{(Nb, Ti)ss} // (002)_{α-(Nb, Ti)5Si3}. Compared with the AC alloy, the DS increases the mechanical properties of the alloy obviously and the alloy DS at 8 mm/h exhibits the best mechanical properties.