Influence of σ Phase on the Allotropic Transformation of the Matrix in Co-Re-Cr-Based Alloys with Ni Addition
Influence of σ Phase on the Allotropic Transformation of the Matrix in Co-Re-Cr-Based Alloys with Ni Addition
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DOI：
10.3390/met8090706
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发表时间：
2018-09-01
期刊：
影响因子：
2.9
通讯作者：
Christ, Hans-Juergen
中科院分区：
文献类型：
--
作者：
Doerries, Kai;Mukherji, Debashis;Christ, Hans-Juergen
Co-Re-Cr 合金正在开发用于燃气轮机的高温应用。在这些合金中，当Cr含量高于20原子％时，Cr2Re3基σ相是稳定的。正在研究添加镍来部分替代铬，其目的是在不牺牲铬在合金抗氧化性方面的优势的情况下抑制西格玛形成。本研究通过电子显微镜研究了不同 Cr (18-23%) 和 Ni (8-25%) 合金的微观结构，主要是为了研究 Sigma 相的稳定性及其对 Co 基体相变的影响。在这些合金中，西格玛相主要以两种形态存在，其中在高温下，晶界处仅存在块状西格玛相，但在较低热处理温度下，通过晶粒内的不连续沉淀形成细胞西格玛相。细小细胞σ相的存在影响合金硬度。此外，西格玛析出会耗尽Re基体，也会影响Co基体的同素异形转变。
Co-Re-Cr alloys are being developed for high-temperature application in gas turbines. In these alloys, the Cr2Re3-based sigma phase is stable when the Cr content is higher than 20 atomic %. The addition of Ni is being studied to partially substitute Cr, which aims to suppress sigma formation without sacrificing the benefit of Cr in the oxidation resistance of the alloy. The microstructure of the alloys with varying Cr (18-23%) and Ni (8-25%) was investigated by electron microscopy in the present study, primarily to look into the stability of the sigma phase and its influence on the Co matrix phase transformation. The sigma phase is mainly found in two morphologies in these alloys, where at high temperature only blocky sigma phase is present at grain boundaries but cellular sigma is formed through a discontinuous precipitation within the grains at lower heat treatment temperatures. The presence of fine cellular sigma phase influences the alloy hardness. Moreover, the sigma precipitation, which depletes the matrix in Re, also influences the allotropic transformation of the Co matrix.