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金属学报  2020, Vol. 56 Issue (2): 203-211    DOI: 10.11900/0412.1961.2019.00100
  研究论文 本期目录 | 过刊浏览 |
冷却速率对β凝固γ-TiAl合金硼化物和室温拉伸性能的影响
王希1,2,刘仁慈1(),曹如心3,贾清1,崔玉友1,杨锐1
1. 中国科学院金属研究所 沈阳 110016
2. 中国科学技术大学材料科学与工程学院 沈阳 110016
3. 三峡大学机械与动力学院 宜昌 443002
Effect of Cooling Rate on Boride and Room Temperature Tensile Properties of β-Solidifying γ-TiAl Alloys
WANG Xi1,2,LIU Renci1(),CAO Ruxin3,JIA Qing1,CUI Yuyou1,YANG Rui1
1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2. College of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3. College of Mechanical and Power Engineering, China Three Gorges University, Yichang 443002, China
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摘要: 

设计了不同厚度台阶铸板以实现冷却速率梯度,采用离心熔模铸造制备了不同冷却速率的β凝固含B γ-TiAl合金样品,研究了冷却速率对硼化物和室温拉伸性能的影响。结果表明,硼化物分布在晶界,其长径比随冷却速率的提高而增大,而形貌由短棒状转变为丝带状。慢冷样品中短棒状TiB为B27结构,而快冷样品中丝带状TiB为Bf结构。2种结构TiB均存在生长各向异性,[010]和[100]分别为Bf和B27结构的最慢生长方向,前者更为显著,这可能与上述方向Ti、B原子周期性间隔排列,原子短程重排更为困难有关。随着冷却速率提高,材料屈服强度提高,但室温塑性下降,这与快冷样品中的细长丝带状硼化物容易萌生裂纹并迅速扩展有关;慢冷样品中的短棒状硼化物不易萌生裂纹,相应室温塑性较好。

关键词 γ-TiAl合金β凝固熔模铸造冷却速率硼化物拉伸性能    
Abstract

β-solidifying γ-TiAl alloys have attracted much attention for their higher specific strength and better mechanical properties at elevated temperature. They usually need some boron addition to refine the lamellar grain size, which is believed to improve their poor room temperature ductility. However, the boron addition may cause some side effects on mechanical properties for the formation of borides with unfavorable morphology and crystal structure, which is severely influenced by the alloy composition and cooling rate during casting. The components of γ-TiAl applied usually have complex structure, such as different thicknesses, which leads to different cooling rates and therefore different microstructures and mechanical properties. To evaluate the influence of cooling rate on the microstructure and mechanical properties of γ-TiAl investment casting, plate with step thicknesses was designed to achieve different cooling rates. Step plates of β-solidifying boron-containing TiAl alloy were fabricated by centrifugal casting in Y2O3 facing coating ceramic moulds. It was found that boride mainly distributed on grain boundary, and its aspect ratio increased with increasing cooling rate, with its morphology varying from short, flat plate to long, curvy ribbon. The short plate and curvy ribbon borides were TiB with B27 and Bf structure, respectively. Both types of boride exhibit anisotropic growth characteristics (especially for Bf structure), with the slowest growth rate along [100] and [010] for B27 structure and Bf structure, respectively. This is attributed to the difficulty of atomic rearrangement along corresponding directions during solidification. The cooling rate increase caused the increase of yield strength but the decrease of room temperature ductility, the former results from the decreasing of grain size and lamellar spacing, while the latter results from the easy cracking nucleation and propagation of the long curvy boride, leaving smooth curvy surfaces on the fracture surface. Samples containing short flat plate boride showed better ductility, and no smooth curvy surface was observed.

Key wordsγ-TiAl alloy    β-solidifying    investment casting    cooling rate    boride    tensile property
收稿日期: 2019-04-03     
ZTFLH:  TG146.2  
基金资助:国家自然科学基金项目(51701209);国家重点研发计划项目(2016YFB0701304);国家重点研发计划项目(2016YFB0701305)
通讯作者: 刘仁慈     E-mail: rcliu@imr.ac.cn
Corresponding author: Renci LIU     E-mail: rcliu@imr.ac.cn
作者简介: 王 希,男,1995年生,硕士生

引用本文:

王希,刘仁慈,曹如心,贾清,崔玉友,杨锐. 冷却速率对β凝固γ-TiAl合金硼化物和室温拉伸性能的影响[J]. 金属学报, 2020, 56(2): 203-211.
Xi WANG, Renci LIU, Ruxin CAO, Qing JIA, Yuyou CUI, Rui YANG. Effect of Cooling Rate on Boride and Room Temperature Tensile Properties of β-Solidifying γ-TiAl Alloys. Acta Metall Sin, 2020, 56(2): 203-211.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2019.00100      或      https://www.ams.org.cn/CN/Y2020/V56/I2/203

图1  台阶状铸板示意图
图2  台阶状铸板不同位置热等静压及热处理后显微组织的OM、BSE-SEM和SE-SEM像
图3  4和12 mm厚样品热等静压和热处理后的晶界SE-SEM像及其组成相β和硼化物的EDS分析
PositionPhaseTiAlNbMo
1β53.2538.545.153.06
2Boride62.5827.817.991.62
表1  图3a和b中不同位置EDS分析结果 (atomic fraction / %)
图4  4和12 mm厚度铸板片层组织的TEM明场像
图5  4和12 mm厚铸板中硼化物TEM明场像及其SAED花样
图6  不同厚度样品的室温拉伸应力-应变曲线

Thickness

mm

No.

Yield strength

MPa

Ultimate strength

MPa

Elongation

%

417327440.27
27177330.29
816837430.57
26717200.47
1216667931.17
26667560.79
表2  不同厚度铸板的室温拉伸性能
图7  4和12 mm厚度样品断口宏观形貌和裂纹形核处形貌及其BSE-SEM像
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