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金属学报  2017, Vol. 53 Issue (5): 583-591    DOI: 10.11900/0412.1961.2016.00502
  论文 本期目录 | 过刊浏览 |
直流电流对Ti-48Al-2Cr-2Nb合金组织和性能的影响
陈占兴,丁宏升,刘石球,陈瑞润,郭景杰,傅恒志
哈尔滨工业大学材料科学与工程学院金属精密热加工国家级重点实验室 哈尔滨 150001
Effects of Direct Current on Microstructure and Properties of Ti-48Al-2Cr-2Nb Alloy
Zhanxing CHEN,Hongsheng DING,Shiqiu LIU,Ruirun CHEN,Jingjie GUO,Hengzhi FU
National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
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摘要: 

将直流电流作用于定向凝固过程中的Ti-48Al-2Cr-2Nb合金,利用OM、XRD、SEM和TEM分析了合金的凝固组织、相组成和片层组织,测试了合金的显微硬度及800 ℃压缩力学性能。结果表明,电流在一定程度上促进了合金凝固组织的细化及成分的均匀性,减少或消除了片层间偏析。随着电流密度的增大,平均晶粒尺寸和片层厚度呈现先减小后增大的趋势,α2相相对含量先增大而后减小,合金的显微硬度、压缩断裂与屈服强度也呈现先增大后减小的趋势。平均晶粒尺寸最小约0.46 mm,片层间距最小为0.19 μm,分别比未加载电流时降低70%和29%,α2相相对含量从18.5%增至39.4%。片层间距或晶粒尺寸越小,合金的强度越高,变形能力越均匀,塑性也越好。合金的最大显微硬度达542 HV,合金的压缩屈服强度与断裂强度分别达到1200和1365 MPa,与未施加电流时相比均有所提高。加载直流电流引起固-液界面相前沿过冷度减小,可认为是TiAl二元相图中的L→β+L→α+β的包晶反应成分向富Al侧微小偏移,此时初生β相增多,从而造成了TiAl合金室温相组织α2相的相对含量增加。

关键词 TiAl合金直流电流凝固微观组织显微硬度高温压缩    
Abstract

TiAl based alloys have been widely used as promising aerospace structural materials, which benefit from their unique combination of mechanical properties. However, they yield poor plasticity and low process ability, thus restricting the wide application. In this work, an efficient way was proposed by which direct current (DC) was imposed on the solidification process of TiAl-based alloy. Influences of DC on the microstructure and properties of directionally solidified Ti-48Al-2Cr-2Nb alloy using water cold crucible directional solidification equipment has been investigated. The changes of solidification microstructure, phase structure and composition of the alloy and γ/α2 interlamellar structures were characterized by OM, XRD, SEM and TEM. The effect of DC on the size of eutectoid colony, interlamellar spacing and relative content of α2 phase had been studied by Image Pro Plus. Furthermore, the mechanical properties of the directionally solidified Ti-48Al-2Cr-2Nb alloy at 800 ℃ were performed. The results revealed that the DC can evidently promote the homogeneity of the solidification component and refiner the structure, and the segregation in lamellar colonies can be efficiently reduced or eliminated to a certain extent. With the increasing of the current density, the grain size and lamellar spacing decreased first and then increased, however, the α2 phase content showed a totally different trend. Moreover, the microhardness, compression yield strength and the fracture strength of the alloy also revealed a trend of decrease after the first increase too. With the current density increasing, the average grain size and interlamellar spacing declined to the lowest of 0.46 mm and 0.19 μm, respectively, and the content of α2 phase increased from 18.5% to 39.4%. The microhardness of sample reached 542 HV, the compression yield strength and the fracture strength were remarkably improved, and the maximum values reached 1200 and 1365 MPa, respectively. DC can cause a reduction of the supercooling in front of the liquid phase during the solidification process. The results can be seen as the peritectic reaction L→β+L→α+β moving a tiny drift to the direction of the Al-rich side in TiAl binary phase diagram, consequently, the primary β-phase increased, and the content of α2 phase, microstructure under room temperature, increased evidently.

Key wordsTiAl alloy    direct current    solidification    microstructure    microhardness    high temperature compression
收稿日期: 2016-11-11      出版日期: 2017-03-13
基金资助:国家自然科学基金项目Nos.51171053和51471062

引用本文:

陈占兴,丁宏升,刘石球,陈瑞润,郭景杰,傅恒志. 直流电流对Ti-48Al-2Cr-2Nb合金组织和性能的影响[J]. 金属学报, 2017, 53(5): 583-591.
Zhanxing CHEN,Hongsheng DING,Shiqiu LIU,Ruirun CHEN,Jingjie GUO,Hengzhi FU. Effects of Direct Current on Microstructure and Properties of Ti-48Al-2Cr-2Nb Alloy. Acta Metall Sin, 2017, 53(5): 583-591.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2016.00502      或      http://www.ams.org.cn/CN/Y2017/V53/I5/583

图1  直流电流作用下定向凝固Ti-48Al-2Cr-2Nb合金的宏观组织
图2  直流电流作用下Ti-48Al-2Cr-2Nb组织的OM像
图3  直流电流作用下Ti-48Al-2Cr-2Nb合金组织的SEM像
图4  电流作用下Ti-48Al-2Cr-2Nb的XRD谱
图5  直流电流作用下Ti-48Al-2Cr-2Nb合金的片层组织TEM像
图6  直流电流作用下Ti-48Al-2Cr-2Nb合金中的α2相含量变化
图7  直流电流作用下Ti-48Al-2Cr-2Nb合金的晶粒尺寸及片层间距
图8  直流电流作用下定向凝固Ti-48Al-2Cr-2Nb合金各区域的显微硬度
图9  直流电流作用下Ti-48Al-2Cr-2Nb合金的高温压缩真应力-应变曲线
图10  直流电流作用下TiAl二元合金非平衡转变示意图
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