Effect of withdrawal rate on the microstructure of directional solidified Ni-43Ti-4Al-2Nb-2Hf single crystal alloys

Abstract

Single crystals of Ni-43Ti-4Al-2Nb-2Hf (atomic fraction, %) alloy were directionally solidified (DS) using liquid Single crystals of Ni-43Ti-4Al-2Nb-2Hf (atomic fraction, %) alloy were directionally solidified (DS) using liquid metal cooling method by the seeding technique. The preferred crystallographic orientations of single crystals were determined by Electron Backscattered Diffraction (EBSD). The effect of withdrawal rates (5×10-6 m•s-1,1×10-5 m•s-1 and 1.5×10-5 m•s-1) on microstructures was also investigated. The results show that the primary dendritic spacing and the morphology of Ti2Ni phase are markedly influenced by withdrawal rates at the heating temperature of 1600°C even also the solidification pathway of the alloy is changed. As except, the primary dendritic spacing decreases with the increasing withdrawal rate. Moreover, the Ti2Ni phases distribute in interdendritic region in DS samples withdrawn at 5×10-6 m•s-1 and 1×10-5 m•s-1, whereas the Ti2Ni phase solidifies as the primary phase when the withdrawal rate increases to 1.5×10-5 m•s-1.