Microstructure evolution of eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf alloy processed by directional solidification
Microstructure evolution of eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf alloy processed by directional solidification
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DOI：
10.1007/s12598-015-0649-4
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发表时间：
2017-06
期刊：
影响因子：
8.8
通讯作者：
Zhen Li;S. Yuan;L. Jia;B. Kong;Zhen Hong;Hu Zhang
中科院分区：
文献类型：
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作者：
Zhen Li;S. Yuan;L. Jia;B. Kong;Zhen Hong;Hu Zhang
在这项工作中，近共晶Nb-24 Ti-15 Si-4Cr-2Al-2 Hf（at%）合金在1900 °C下以6、18、36、50 mm·min− 1的抽拉速率定向凝固，然后在1450 °C下热处理12 h。研究了显微组织的演变。结果表明：在整个抽拉速率范围内，定向凝固合金的组织均为Nb + Nb 5Si 3共晶，但抽拉速率的变化对定向凝固合金的凝固路线、Nb + Nb 5Si 3共晶团的形貌和尺寸有很大影响。随着抽拉速率的增加，花瓣状的Nb_3 + Nb_5Si_3共晶团转变为颗粒状。热处理后，Nb 5Si 3相逐渐形成网状结构，使Nb 5Si 3相隔离，相界变得更加平滑，从而降低了界面能。热处理样品中存在两种Nb 5Si 3相，分别为α-Nb 5Si 3和γ-Nb 5Si 3。该研究对Nb-Si基合金力学性能的优化具有重要的指导意义。
In this work, the near-eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf (at%) alloy was directionally solidified at 1900 °C with withdrawal rates of 6, 18, 36, 50 mm·min−1and then heat-treated at 1450 °C for 12 h. The microstructure evolution was investigated. The results show that the microstructure of the directionally solidified (DS) alloy is composed of Nbss+ Nb5Si3eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes, the morphology and size of Nbss+ Nb5Si3eutectic cells. With the increase in withdrawal rates, the petaloid Nbss+ Nb5Si3eutectic cells transform into granular morphology. After the heat treatment, a mesh structure Nbssis formed gradually which isolates the Nb5Si3, and the phase boundaries become smoother in order to reduce the interfacial energy. Moreover, two kinds of Nb5Si3exist in the heat-treated (HT) samples identified by crystal form and element composition, which are supposed as α-Nb5Si3and γ-Nb5Si3, respectively. This study exhibits significant merits in guiding the optimization of Nb–Si-based alloys’ mechanical properties.