A study of the microstructures and oxidation of Nb-Si-Cr-Al-Mo in situ composites alloyed with Ti, Hf and Sn
A study of the microstructures and oxidation of Nb-Si-Cr-Al-Mo in situ composites alloyed with Ti, Hf and Sn
复制标题
DOI：
10.1016/j.intermet.2006.08.016
复制
发表时间：
2007-03-01
期刊：
影响因子：
4.4
通讯作者：
Tsakiropoulos, Panos
中科院分区：
文献类型：
--
作者：
Geng, Jie;Tsakiropoulos, Panos
研究了合金化对Nb-Ti-Si-Al-Cr-Nlo-Hf-Sn系Nb-ss/Nb_5Si_3基原位复合材料的组织、凝固路径、相稳定性和氧化动力学的影响。所有研究的合金被归类为过共晶铌硅化物基原位复合材料，并具有较低的密度相比，镍基高温合金。Nb 3Si硅化物在不含Hf的合金中形成，并在1500 ℃的热处理期间转变为Nb-ss和α Nb 5Si 3。通过添加Ti增强了这种转变。Nb_5Si_3和Nb_5Si_3是无Hf合金显微组织中的平衡相。在Ti的存在下，β Nb 5Si 3仅部分转化为α Nb 5Si 3，表明Ti使β Nb 5Si 3稳定到较低温度（至少到1300 ℃）。此外，与Hf的合金化稳定的六方晶系的γ Nb 5Si 3（Mn 5Si 3型）硅化物在含Hf的合金。Sn的加入促进了富Si C14 Laves相的形成，并使其在1300 ℃下稳定。这是由于Sn的加入降低了Cr在Nb-Ti-Si-Al-Cr-Mo-Hf-Sn系Nb-ss中的溶解度，同时增加了Si的溶解度。Si在C14 Laves相中的溶解度在类似于6.6至10.5原子%的范围内。在每种合金中的Nb-ss的晶格参数增加后，热处理意味着Nb-ss和金属间相之间的溶质的重新分配。通过与Ti和Sn合金化，合金在800 ℃和1200 ℃下的抗氧化性显著增加。Nb-18 Si-5Al-5Cr-5 Mo（铸态）、Nb-24 Ti-18 Si-5Al-5Cr-5 Mo（铸态）、Nb-24 Ti-18 Si-5Al-5Cr-2 Mo（热处理）和Nb-24 Ti-18 Si-5Al-5Cr-2 Mo-5 Hf（热处理）合金在800 ℃下表现出有害氧化行为。在Nb-24 Ti-Si 5Al-5Cr-2 Mo-5 Hf-5Sn合金中，在800 ℃下消除了有害物，表明Sn的添加在控制中等温度下有害物的氧化行为中起重要作用。所有合金在800 ℃和1200 ℃下的氧化行为由Nb-ss的氧化控制，并且对合金中Nb-ss的面积分数敏感。(c)2006爱思唯尔有限公司保留所有权利。
The effects of alloying on the microstructures, solidification path, phase stability and oxidation kinetics of Nb-ss/Nb5Si3 base in situ composites of the Nb-Ti-Si-Al-Cr-Nlo-Hf-Sn system have been investigated in this study. All the studied alloys are classified as hyper-eutectic Nb silicide base in situ composites and have lower densities compared to nickel-based superalloys. The Nb3Si silicide formed in the Hf-free alloys and transformed to Nb-ss and alpha Nb5Si3 during heat treatment at 1500 degrees C. This transformation was enhanced by the addition of Ti. The Nb-ss and Nb5Si3 were the equilibrium phases in the microstructures of the Hf-free alloys. In the presence of Ti, the beta Nb5Si3 only partially transformed to alpha Nb5Si3, suggesting that Ti stabilises the beta Nb5Si3 to lower temperatures (at least to 1300 degrees C). Furthermore, alloying with Hf stabilised the hexagonal gamma Nb5Si3 (Mn5Si3-type) silicide in the Hf-containing alloys. The addition of Sn promoted the formation of the Si-rich C14 Laves phase and stabilised it at 1300 degrees C. This is attributed to the Sn addition decreasing the solubility of Cr in the Nb-ss of the Nb-Ti-Si-Al-Cr-Mo-Hf-Sn system whilst increasing the Si solubility. The Si solubility in the C14 Laves phase was in the range similar to 6.6 to 10.5 at%. The lattice parameter of the Nb-ss in each alloy increased after heat treatment signifying the redistribution of solutes between the Nb-ss and the intermetallic phases. The oxidation resistance of the alloys at 800 degrees C and 1200 degrees C increased significantly by alloying with Ti and Sn. Pest oxidation behaviour was exhibited by the Nb-18Si-5Al-5Cr-5Mo (as cast), Nb-24Ti-18Si-5Al-5Cr-5Mo (as cast), Nb-24Ti-18Si-5Al-5Cr-2Mo (heat treated) and Nb-24Ti-18Si-5Al-5Cr-2Mo-5Hf (heat treated) alloys at 800 degrees C. Pesting was eliminated in the alloy Nb-24Ti-Si5Al-5Cr-2Mo-5Hf-5Sn at 800 degrees C, indicating that the addition of Sn plays an important role in controlling the pest oxidation behaviour at intermediate temperatures. The oxidation behaviour of all the alloys at 800 degrees C and 1200 degrees C was controlled by the oxidation of the Nb-ss and was sensitive to the area fraction of Nb-ss in the alloy. (c) 2006 Elsevier Ltd. All rights reserved.