Suzuki segregation in Co-Ni-based superalloy at 973 K: An experimental and computational study by phase-field simulation
- 作者：Yuichiro Koizumi ; koizumi@imr.tohoku.ac.jp ; Takeshi Nukaya ; Sho Suzuki ; Shingo Kurosu ; Yunping Li ; Hiroaki Matsumoto ; Kazuhisa Sato ; Yuji Tanaka ; Akihiko Chiba
- 关键词：Strain-aging ; Transmission electron microscopy (TEM) ; Refractory metals ; Interface segregation ; Phase field models
- 刊名：Acta Materialia
- 出版年：2012
- 期刊代码：1_13596454
- 类别：ms
- 出版时间：April, 2012
- 卷：60
- 期：6-7
- 页码：2901-2915
- 文件大小：2573 K
摘要
Suzuki segregation in Co-Ni-based superalloys is of longstanding interest. In this study, the development of widely extended stacking fault (SF) ribbons was confirmed in a Co-Ni-based superalloy aged at 973 K after deformation at room temperature, which supports the decrease in stacking fault energy (SFE) due to Suzuki segregation. In addition, the plastic deformation behaviors of Co-Ni-based superalloys with various Nb contents up to 3 wt.%were investigated focusing on the effect of Nb addition on dynamic strain-aging by Suzuki segregation. The negative strain-rate dependence of flow stress due to dynamic strain-aging became more significant with increasing Nb content; however, attempts to detect segregating elements by scanning transmission electron microscopy and energy-dispersive spectroscopy analysis were not successful. A phase-field simulation of Suzuki segregation suggested strong Ni depletion with segregation of Cr and Mo atoms at the SF, and the SFE can become negative as a consequence of the segregation. This agrees with the experimentally observed formation of wide SFs by the aging at 973 K after cold deformation. It is also suggested that Nb atoms are strongly depleted at SFs, and a small amount of Nb addition dramatically enhances Cr segregation, resulting in further decreases in the SFE, which is probably responsible for the observed enhancement of dynamic strain-aging by Nb addition. In addition, the local structural changes, such as short-range ordering and/or an in-plane ordering, accompanying the segregation were discussed as possible additional mechanisms for strain-aging enhancement.