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金属学报  2019, Vol. 55 Issue (6): 692-700    DOI: 10.11900/0412.1961.2019.00007
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电子束快速成形制备TC4合金的组织和拉伸性能分析
刘征1,2,刘建荣1(),赵子博1,王磊1,王清江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
Microstructure and Tensile Property of TC4 Alloy Produced via Electron Beam Rapid Manufacturing
Zheng LIU1,2,Jianrong LIU1(),Zibo ZHAO1,Lei WANG1,Qingjiang WANG1,Rui YANG1
1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2. School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
引用本文:

刘征,刘建荣,赵子博,王磊,王清江,杨锐. 电子束快速成形制备TC4合金的组织和拉伸性能分析[J]. 金属学报, 2019, 55(6): 692-700.
Zheng LIU, Jianrong LIU, Zibo ZHAO, Lei WANG, Qingjiang WANG, Rui YANG. Microstructure and Tensile Property of TC4 Alloy Produced via Electron Beam Rapid Manufacturing[J]. Acta Metall Sin, 2019, 55(6): 692-700.

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摘要: 

针对电子束快速成形(EBRM)钛合金的组织特点,采用OM、SEM、XRD和TEM等实验手段,分析了EBRM制备TC4合金的微观组织和织构对其拉伸性能的影响规律。结果表明:TC4合金存在着平行于沉积方向的β柱状晶,且柱状晶的宽度随着沉积高度的增加,初始时迅速增加,之后增加的趋势变缓。由于沉积过程中循环的热作用,柱状晶内α片尺寸随着沉积高度的增加而减小。合金存在典型的转变α相织构。微观结构的梯度变化也导致了合金在不同位置的拉伸性能差异。随着X方向拉伸试样位置的升高,合金的屈服强度没有明显的变化,但抗拉强度有所提升;合金的塑性呈现上升的趋势。在合金底部,距离基板10和20 mm处的拉伸试样具有相近的加工硬化指数,低于合金中间的拉伸试样,而合金顶端拉伸试样的加工硬化指数较高。此外,合金还具有拉伸性能的各向异性,45°方向拉伸试样的强度高于X方向和Z方向的拉伸试样,同时Z方向拉伸试样的强度最低,这种强度各向异性主要归因于合金的转变α相织构。

关键词 电子束快速成形TC4合金显微组织织构拉伸性能    
Abstract

Electron beam rapid manufacturing (EBRM) is one of the 3D printing technologies. The main attractions of EBRM technology are its high efficiency and economy in fabricating large, complex near net shape components dielessly and only needing limited machining. In general, the microstructure and texture of titanium alloy can play a significant role in determining its mechanical behaviors. In the present work, the microstructure, texture and tensile property of TC4 alloy produced by electron beam rapid manufacturing (EBRM) are investigated. Results show that the microstructure is comprised of columnar prior β grains that orient parallel to the building direction. The width of the columnar β grains increased rapidly at the initial several build layers, and the subsequent increase rate of the width of the columnar β grains tends to slow down. Fine α lamellae with gradient size are observed inside the columnar prior β grains, which occur because the alloy experiences different complex thermal histories during the EBRM-produced process. The size of α lamellae tends to decrease with the increase of build layers. The XRD result shows that the TC4 alloy has a typical α phase texture, (the c-axes are either concentrated at about 45° or are perpendicular to the building direction). At the same time, the <$10\bar{1}0$> poles are relative to random distribution. For the tensile samples along the electron beam scanning direction, the yield strengths do not show significant change with the increase of build layers, but the tensile strengths increase. The ductility of the alloy also has an upward trend, despite of a slightly decreasing ductility in the top sample. The tensile samples at the bottom of the alloy (10 mm and 20 mm away from the substrate) have similar work hardening exponents, which are lower than the top sample. The top sample shows the highest work hardening exponent. This difference in the tensile properties can be highly attributed to the gradient microstructure. The alloy also presents obvious anisotropy in tensile strength. The tensile sample along the 45° direction has a higher strength than the sample along the X direction, while the tensile sample along the Z direction shows the lowest strength. This anisotropic strength is strongly associated with the α phase texture. When the loading direction is 45° to the building direction, most of the c-axes of α phase are about parallel to the loading direction, showing a "hard" orientation, leading to a higher strength than other oriented samples. Conversely, when the loading direction is along the building direction, most of the α phase present a "soft" orientation, resulting in lower strength compared to the tensile samples along the 45° or the X direction.

Key wordsEBRM    TC4 alloy    microstructure    texture    tensile property
收稿日期: 2019-01-09     
ZTFLH:  TG14  
基金资助:国家重点研发计划项目(No.2017YFB1103100);中国航空工业科学基金项目(No.20175492002)
作者简介: 刘 征,男,1989年生,博士生
图1  电子束快速成形(EBRM)制备TC4合金的示意图和拉伸试样的取样位置示意图
图2  EBRM制备TC4合金X-Z面的OM像
图3  原始β晶粒和α板条宽度与沉积高度的关系
图4  EBRM制备TC4合金不同部位的SEM像
图5  TC4合金α相的{0001}和{101ˉ0}极图
图6  平行于X方向的拉伸试样在不同高度的力学性能
图7  拉伸试样的对数真应力-对数真应变曲线(应变2.5%~4.6%)和加工硬化指数
图8  TC4合金不同部位的TEM像
图9  EBRM制备TC4合金不同取向试样的拉伸强度
图10  晶粒沿不同拉伸方向的滑移程示意图
图11  TC4合金沿不同拉伸方向的反极图
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