论文部分内容阅读
In this work, the near-eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf(at%) alloy was directionally solidified at 1900 ℃ with withdrawal rates of 6, 18, 36, 50 mm·min~(-1) and then heat-treated at 1450 ℃ for 12 h. The microstructure evolution was investigated. The results show that the microstructure of the directionally solidified(DS) alloy is composed of Nb_(ss)+Nb_5Si_3 eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes,the morphology and size of Nb_(ss)+Nb_5Si_3 eutectic cells.With the increase in withdrawal rates, the petaloid Nb_(ss)+Nb_5Si_3 eutectic cells transform into granular morphology. After the heat treatment, a mesh structure Nbssis formed gradually which isolates the Nb_5Si_3, and the phase boundaries become smoother in order to reduce the interfacial energy. Moreover, two kinds of Nb_5Si_3 exist in the heat-treated(HT) samples identified by crystal form and element composition, which are supposed as α-Nb_5Si_3 and γ-Nb_5Si_3, respectively. This study exhibits significant merits in guiding the optimization of Nb–Si-based alloys’ mechanical properties.
In this work, the near-eutectic Nb-24Ti-15Si-4Cr-2Al-2Hf (at%) alloy was directionally solidified at 1900 ℃ with withdrawal rates of 6, 18, 36 and 50 mm · min -1 The results show that the microstructure of the directionally solid (DS) alloy is composed of Nb_ (ss) + Nb_5Si_3 eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes, the morphology and size of Nb_ (ss) + Nb_5Si_3 eutectic cells. The increase in withdrawal rates, the petaloid Nb_ (ss) + Nb_5Si_3 eutectic cells transform into granular morphology. heat treatment, a mesh structure Nbssis formed gradually which iso boundaries the ni_5Si_3, and the phase boundary become smoother in order to reduce the interfacial energy. composition, which are supposed as α-Nb_5Si_3 and γ-Nb_5Si_3, respectively. This study shows significant merits in guiding the optimization of Nb-Si-based alloys’ mechanical properties.