Sigma phase evolution in Co-Re-Cr-based alloys at 1100 °C
Sigma phase evolution in Co-Re-Cr-based alloys at 1100 °C
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DOI：
10.1016/j.intermet.2013.11.003
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发表时间：
2014-05-01
期刊：
影响因子：
4.4
通讯作者：
Roesler, Joachim
中科院分区：
文献类型：
--
作者：
Depka, Timo;Somsen, Christoph;Roesler, Joachim
Co-Re基合金是一种新型的金属体系，具有可开发的成分范围宽、熔化温度高等特点。通过合金化铬可以改善二元体系较差的抗氧化性。然而，添加铬也会导致Cr2Re3型Sigma相的出现。在本研究中，我们研究了三种基于Co-17Re-23Cr(at.%)三元组分的合金在1100℃蠕变和时效过程中σ相的演变。在所有合金中，Sigma相以块状形态填充在六方密堆积(HCP)相的晶界上。此外，在初始加工过程中或在热暴露过程中形成的片层σ相在颗粒内部形成了细小的弥散。这种沉淀是通过细胞反应进行的，该反应将过饱和的hcp相转变为近平衡hcp相和sigma相的交替片层。因此，这一过程具有不连续降水的特点。利用取向成像显微镜，我们观察到片层之间的取向关系，它描述了hcp相的基面与四方sigma相的原子基层形成的共格界面。在1100摄氏度的长期热暴露后，片层结构的过度老化导致Sigma片层的球化和随后的Ostwald成熟。(C)2013爱思唯尔有限公司。保留所有权利。
Co-Re-based alloys have been introduced as a novel metallic system that possesses a wide exploitable composition range and high melting temperatures. The poor oxidation resistance of the binary system can be improved by alloying chromium. However, adding chromium also leads to the occurrence of the sigma phase of type Cr2Re3. In the present study, we investigate the evolution of the sigma phase during creep and aging at 1100 degrees C for three selected alloys based on the ternary composition Co-17Re-23Cr (at.%). In all alloys, sigma phase populates the grain boundaries of the hexagonally close-packed (HCP) matrix phase in a blocky morphology. Additionally, a fine dispersion of lamellar sigma phase in the grain interiors has formed during the initial processing or forms during thermal exposure. This precipitation takes place by a cellular reaction that transforms a supersaturated HCP phase into alternating lamellae of a near-equilibrium HCP phase and the sigma phase. The process therefore has the character of a discontinuous precipitation. Using orientation imaging microscopy, we observe an orientation relationship between the lamellae, which describes the basal plane of the HCP phase to form a coherent interface with the base layer of atoms of the tetragonal sigma phase. After long-term thermal exposure to 1100 degrees C, overaging of the lamellar structure results in spheroidization of the sigma lamellae and subsequent Ostwald ripening. (C) 2013 Elsevier Ltd. All rights reserved.