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金属学报  2018, Vol. 54 Issue (3): 419-427    DOI: 10.11900/0412.1961.2017.00144
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低偏析异质籽晶制备单晶高温合金的籽晶熔合区形成机制研究
郭静1,2, 李金国2(), 刘纪德2, 黄举2,3, 孟祥斌2, 孙晓峰2
1 中国科学院大学 北京 100049
2 中国科学院金属研究所 沈阳 110016
3 东北大学材料科学与工程学院 沈阳 110819
Formation Mechanism of Fusion Zone in Growth of Single Crystal Superalloy with Low-Segregated Heterogeneous Seed
Jing GUO1,2, Jinguo LI2(), Jide LIU2, Ju HUANG2,3, Xiangbin MENG2, Xiaofeng SUN2
1 University of Chinese Academy of Science, Beijing 100049, China
2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
3 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
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摘要: 

采用低偏析异质籽晶法研究了定向凝固制备单晶高温合金时籽晶熔合区的形成机制,利用SEM和EPMA对籽晶熔合区的组织以及元素分布进行分析。结果表明,籽晶回熔平衡界面前沿存在一个无微观偏析的熔合区,该区域是凝固界面发生平面状-胞状失稳转变的过渡区。增加籽晶材料中W含量或提高定向凝固速率均会促进凝固界面的平面状-胞状失稳转变,且凝固速率的影响更显著。相比于传统籽晶法,低偏析异质籽晶熔合区内的平界面凝固能有效避免籽晶回熔界面的枝晶熔断和成分过冷导致的杂晶形核,从而提高单晶的引晶生长成功率。

关键词 镍基单晶高温合金籽晶凝固界面熔合区    
Abstract

Seeding technique is a promising method for growing single crystal superalloy blade. However, sometimes stray grains nucleate in the transformation process of single crystal structure from a seed, which always cause failure of single crystal growth. In order to obtain single crystal with high perfection structure, Ni-based single crystal superalloy was prepared with low-segregated seeds by high rate solidification (HRS) method in the dual heating zone furnace. The melt-back zones of seeds were investigated systematically, and the results showed that a fusion zone without microsegregation exists in front of the melt-back equilibrium interface of seeds, in which solidification interface transited from planar to cellular. Further experiments showed that increasing the W content of seeds or the solidification rate can both accelerate the whole non-steady transition process and make fusion zone shrink. Compared with the traditional seeding method, the low segregated heterogeneous seeding technique can increase the casting yield by avoiding the nucleation of stray grains in the fusion zone, which caused by the pinched-off secondary dendrites and constitutional undercooling.

Key wordsNi-based single crystal superalloy    seed    solidification interface    fusion zone
收稿日期: 2017-04-21     
基金资助:资助项目 国家自然科学基金项目Nos.51331005和U1508213
作者简介:

作者简介 郭 静,男,1991年生,硕士

引用本文:

郭静, 李金国, 刘纪德, 黄举, 孟祥斌, 孙晓峰. 低偏析异质籽晶制备单晶高温合金的籽晶熔合区形成机制研究[J]. 金属学报, 2018, 54(3): 419-427.
Jing GUO, Jinguo LI, Jide LIU, Ju HUANG, Xiangbin MENG, Xiaofeng SUN. Formation Mechanism of Fusion Zone in Growth of Single Crystal Superalloy with Low-Segregated Heterogeneous Seed. Acta Metall Sin, 2018, 54(3): 419-427.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2017.00144      或      https://www.ams.org.cn/CN/Y2018/V54/I3/419

Specimen Vw Nominal composition (seed) k
No. mmmin-1 (mass fraction)
1 1 Ni -
2 1 Ni-28%W 1.04
3 1 Ni-35%W 0.99
4 Quenching Ni -
5 Quenching Ni-28%W 1.04
6 Quenching Ni-35%W 0.99
表1  实验样品的工艺参数以及籽晶中溶质元素的偏析系数
图1  抽拉速率为1 mm/min时不同成分低偏析异质籽晶的熔合区形貌
图2  抽拉速率为1 mm/min时3种异质籽晶熔合区组织形貌与溶质分布
图3  抽拉速率为1 mm/min时纯Ni籽晶熔合区的形貌和各元素EPMA面分布
图4  纯Ni籽晶熔合区组织形貌和垂直于凝固方向的元素分布
图5  纯Ni籽晶熔合区沿凝固方向的溶质元素含量变化
图6  熔合区凝固界面形态转变示意图
图7  EPMA测定的高温合金中的溶质元素偏析系数(k)
图8  快速凝固后3种低偏析异质籽晶回熔平衡界面形貌
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