TY - JOUR
T1 - Suzuki segregation in Co-Ni-based superalloy at 973 K
T2 - An experimental and computational study by phase-field simulation
AU - Koizumi, Yuichiro
AU - Nukaya, Takeshi
AU - Suzuki, Sho
AU - Kurosu, Shingo
AU - Li, Yunping
AU - Matsumoto, Hiroaki
AU - Sato, Kazuhisa
AU - Tanaka, Yuji
AU - Chiba, Akihiko
N1 - Funding Information:
The authors are grateful to Prof. Samuel M. Allen of Massachusetts Institute for Technology for fruitful discussion on the phase-field modeling of stacking fault. This research was supported by a Regional Innovation Cluster Program 2010 from Ministry of Education, Culture, Sports, Science and Technology of Japan. This research was partly supported by the ISIJ Research Promotion and a Grant-in-Aid for Scientific Research Development from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
PY - 2012/4
Y1 - 2012/4
N2 - 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.
AB - 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.
KW - Interface segregation
KW - Phase field models
KW - Refractory metals
KW - Strain-aging
KW - Transmission electron microscopy (TEM)
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U2 - 10.1016/j.actamat.2012.01.054
DO - 10.1016/j.actamat.2012.01.054
M3 - Article
AN - SCOPUS:84862808247
VL - 60
SP - 2901
EP - 2915
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
IS - 6-7
ER -