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Acta Metall Sin  2020, Vol. 56 Issue (7): 969-978    DOI: 10.11900/0412.1961.2019.00396
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Influence of Secondary Orientation on Competitive Grain Growth of Nickel-Based Superalloys
ZHANG Xiaoli1, FENG Li2, YANG Yanhong3, ZHOU Yizhou3, LIU Guiqun1()
1. School of Materials Science and Engineering, North Minzu University, Yinchuan 750021, China
2. Electrical Engineering, Shengyang Polytechnic College, Shenyang 110045, China
3. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
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Directional solidification (DS) has been widely used to produce aero-engine and gas turbine blades of nickel-based superalloys. The preferred crystallographic orientation of nickel-based superalloys is [001], so the [001] columnar-grain structure can form after DS. Due to the low Young's modulus and the elimination of transverse grain boundaries, the [001] columnar-grain structure has beneficial mechanical behavior. The competitive grain growth dominates the production of columnar grains. There are two views about competitive grain growth, which are consistent for diverging grains but not consistent for converging grains. In the case of convergence of the first view, the grain boundary (GB) was parallel to the favorably aligned dendrites, which indicates that the favorably aligned grain cannot be eliminated. For converging grains of the second view, not only the favorably aligned dendrites could block unfavorably aligned ones, but also the unfavorably aligned dendrites could block favorably aligned ones. Thus, the converging grain boundary moved from unfavorably aligned grain to favorably aligned grain. Finally, the favorably aligned grain may be eliminated. The study about the two views was carried out in the case of the same secondary orientation but did not taken into account the secondary orientation. Up to now, the literatures about the effect of secondary dendrite orientation on competitive growth is rarely and their views contradict with each other. In this work, the bi-crystal and ter-crystal plates with different secondary orientations were produced to study the influence of secondary orientation on competitive grain growth. For the bi-crystal with the same primary orientation, as the secondary GB angle increased, the GB was nearly at the middle of the plate sample, which indicated that the competitive grain growth was weak and could be neglected. For the ter-crystal with different primary orientations, not the secondary orientation but the primary orientation could obviously affect competitive grain growth. In the case of converging grains, the change of secondary dendrite orientation had no effect on the competitive growth behavior and grain growth rate; the favorably and unfavorably aligned dendrites could block each other, which disagreed with Walton-Chalmers model and in good agreement with the results of Zhou. In the case of diverging grains, the result agreed with Walton-Chalmers model and Zhou's result.

Key words:  Ni-based superalloys      directional solidification      competitive grain growth      secondary orientation     
Received:  20 November 2019     
ZTFLH:  TG132.3,TG21  
Fund: National Natural Science Foundation of China(51701210);National Natural Science Foundation of China(21865001);Key Research and Development Program of Ningxia(2019BDE03016);Natural Science Foundation of Ningxia(2018AAC03250)
Corresponding Authors:  LIU Guiqun     E-mail:

Cite this article: 

ZHANG Xiaoli, FENG Li, YANG Yanhong, ZHOU Yizhou, LIU Guiqun. Influence of Secondary Orientation on Competitive Grain Growth of Nickel-Based Superalloys. Acta Metall Sin, 2020, 56(7): 969-978.

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Fig.1  Schematic diagrams showing the mechanism of grain selection in the directional solidification process (Grains A1/A2 and B are favorably and unfavorably oriented grains, respectively; ΔZA, ΔZB—undercooling of grains A and B, respectively)
(a) Walton-Chalmers model (b) summary of experimental results
Fig.2  Schematics of the placement of seeds
(a) bi-crystal: seeds A1 and A2 with the same [001] orientation(b) ter-crystal: seeds A1/A2 and B with different [001] orientations
Seed patternExp.[001]orientation[010]/[010]orientation

Withdrawal speed


θA1 / (o)θB / (o)θA2 / (o)θA1 / (o)θB / (o)θA2 / (o)
Table 1  Structural characteristics and casting conditions of samples
Fig.3  Macrographs showing the macrostructures on the longitudinal section (a) and top cross section (b) and OM image showing the microstructure on cross section (c) in Exp.1-9 (a1, a2—dendrites)
Fig.4  Dependence of θGB on secondary grain boundary angle of seeds A1 and A2 in Exp.Ⅰ (θGB—grain boundary misorientation)
Fig.5  OM image showing the microstructures of ter-crystal samples with the same [010]/[100] orientation in Exp.2-2 (White triangles: the blocking of the favorably aligned dendrites; black triangles: the blocking of the unfavorably aligned dendrites; white arrows: the branching of the favorably aligned dendrites; black arrows: the branching of the unfavorably aligned dendrites)
Fig.6  OM images showing the microstructures of ter-crystal samples with different withdrawal speeds of Exp.3-1 (a~d) and Exp.3-2 (e~h) (White triangles: the blocking of the favorably aligned dendrites; black triangles: the blocking of the unfavorably aligned dendrites; white arrows: the branching of the favorably aligned dendrites; black arrows: the branching of the unfavorably aligned dendrites)
(a, e) longitudinal section (b, f) 90 mm transverse section (c, g) 55 mm transverse section (d, h) 10 mm transverse section
Fig.7  Dependence of θGB on secondary grain boundary angle in the cases of convergence and divergence
Fig.8  Disappearance and regeneration of dendrites in directional solidification (a, a1, a2, b, b1, b2—dendrites)
(a) the blocking of the dendrites (white triangle)
(b) the branching of the dendrite (white triangle)
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