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

Abstract

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 Į-(Nb,Ti) 5 Si 3 , (Ti,Nb) 5 Si 3 and (Nb,Ti)ss phases formed the microstructure of the AC alloy, with precipitates of Cr 2 Nb, Dy 2 O 3 and (Nb,Ti) 3 Si along phase or grain boundaries. The DS alignes (Nb,Ti)ss and Į-(Nb,Ti) 5 Si 3 lamellae parallel to the growth direction and refines the eutectic cell, but coarsens the primary Į-(Nb,Ti) 5 Si 3 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 Į-(Nb,Ti) 5 Si 3 phases have an orientation relationship of [110] (Nb,Ti)ss // [310] Į-(Nb,Ti)5Si3 and (002) (Nb,Ti)ss // (002) Į-(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.

Microstructural Characteristics and Mechanical Properties of a Nb/Nb5Si3 based Composite with and without Directional Solidification

“…Additionally, the white particles mainly distribute along phase and grain boundary randomly. [15,19], grey phase sh α-(Nb,Ti) 5 Si 3 and the grey-white matrix should be (Nb,Ti)ss phase, which form the main structure and grows into eutectic cell. Moreover, the black (Ti,Nb) 5 Si 3 phase tends to precipit grow along eutectic cell boundary forming the semi-continuously necklace shape.…”

“…The further observation reveals that the CC Nb/Nb 5 Si 3 based composite comprises of four kinds of phases. Based on recent researches [15,19], grey phase should be α-(Nb,Ti) 5 Si 3 and the grey-white matrix 4 α-(Nb,Ti) 5 Si 3 and the grey-white matrix should be (Nb,Ti)ss phase, which form the main eutectic structure and grows into eutectic cell. Moreover, the black (Ti,Nb) 5 Si 3 phase tends to precipitate and grow along eutectic cell boundary forming the semi-continuously necklace shape.…”

“…Tian, J.T. Guo the Nb 5 Si 3 strengthening phase [19][20][21]. Based on the recent investigations [22,23], the appropriate rare earth addition could increase the cohesion of phase boundary.…”

“…The further observation reveals that the CC Nb/Nb 5 Si 3 based composite comprises of four kinds of phases. Based on recent researches[15,19], grey phase should be α-(Nb,Ti) 5 Si 3 and the grey-white matrix…”