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金属学报  2019, Vol. 55 Issue (7): 811-820    DOI: 10.11900/0412.1961.2018.00408
  本期目录 | 过刊浏览 |
基于同步辐射X射线成像的选区激光熔化Ti-6Al-4V合金缺陷致疲劳行为
吴正凯1,吴圣川1(),张杰2,宋哲1,胡雅楠1,康国政1,张海鸥3
1. 西南交通大学牵引动力国家重点实验室 成都 610031
2. 中国航空制造技术研究院 北京 100024
3. 华中科技大学数字制造装备与技术国家重点实验室 武汉 430074
Defect Induced Fatigue Behaviors of Selective Laser Melted Ti-6Al-4V via Synchrotron Radiation X-Ray Tomography
Zhengkai WU1,Shengchuan WU1(),Jie ZHANG2,Zhe SONG1,Yanan HU1,Guozheng KANG1,Haiou ZHANG3
1. State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China
2. AVIC Manufacturing Technology Institute, Beijing 100024, China
3. State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
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摘要: 

基于自主研制的原位疲劳试验机和高分辨同步辐射X射线三维成像技术,采用Feret直径和极值统计方法定量表征选区激光熔化Ti-6Al-4V合金的缺陷特征尺寸、数量、位置及形貌,原位观测疲劳裂纹的萌生与扩展行为,通过辨识疲劳断口源区的缺陷特征,开展缺陷诱导的疲劳损伤评价研究,从而建立缺陷特征与疲劳寿命之间的关系。分析表明,缺陷主要为未熔合和气孔,等效直径小于50 μm的频率为90%,球度分布于0.4~0.65之间;在不考虑表面粗糙度的情况下,疲劳裂纹优先在试样表面或近表面缺陷处萌生,呈现出典型的半椭圆形貌;同时缺陷特征尺寸越大,疲劳寿命越低。研究结果为增材高性能部件的疲劳性能及寿命评估提供了重要的理论参考。

关键词 增材制造疲劳寿命评价缺陷演化表征同步辐射三维成像高周疲劳    
Abstract

As a very promising additive manufacturing (AM) technique, selective laser melting (SLM) has gained considerable attentions due to the feasibility of producing light-weight metallic components directly from virtual design data. On the other hand, high strength, low density and high corrosion resistance Ti-6Al-4V alloy has been a preferred AM used material for the aviation and military industries. However, the fatigue damage behaviors of SLMed or AMed components usually suffer from interior defects such as incomplete fusion and gas pores due to unstable process or unsuitable processing parameters. Therefore, thorough investigations on process-induced and metallurgical defects and its influence on the fatigue behavior is required for robust designs and engineering applications of high performance SLM components. As an advanced characterization approach, synchrotron radiation micro computed X-ray tomography (SR-μCT) has been recently to investigate the fatigue damage behaviors of critical components with defects. Based on self-developed in situ fatigue testing rig fully compatible with the BL13W1 at Shanghai Synchrotron Radiation Facility (SSRF), several AMed specimens were prepared for in situ fatigue SR-μCT. The Feret diameter and extreme values statistics were then adopted to characterize the defect size, morphology, population, location and the influence on fatigue life. Fatigue fractography was also examined to further identify the defect to really initiate a fatigue crack. Results show that two types of defects including gas pores and the lack of fusion can be clearly distinguished inside SLM Ti-6Al-4V alloys. Fatigue crack with a typical semi-ellipse usually initiates from the defects at the surface and near the surface. Besides, the defects less than 50 μm and sphericity of 0.4~0.65 dominate for the SLM Ti-6Al-4V alloys. It is also found that the larger the characteristic size of the defect, the lower the fatigue life. Current results can provide a theoretical basis and support to predict the fatigue performance of SLM Ti-6Al-4V alloys. Further investigations should be performed on the relationship between the critical defect and fatigue strength by introducing the Kitagawa-Takahashi diagram.

Key wordsadditive manufacturing    fatigue life assessment    defect evolution characterization    synchrotron radiation three-dimensional tomography    high cycle fatigue
收稿日期: 2018-09-03     
ZTFLH:  TG146.2  
基金资助:国家自然科学基金项目(No.11572267)
通讯作者: 吴圣川     E-mail: wusc@swjtu.edu.cn
Corresponding author: Shengchuan WU     E-mail: wusc@swjtu.edu.cn
作者简介: 吴正凯,男,1994年生,硕士生

引用本文:

吴正凯, 吴圣川, 张杰, 宋哲, 胡雅楠, 康国政, 张海鸥. 基于同步辐射X射线成像的选区激光熔化Ti-6Al-4V合金缺陷致疲劳行为[J]. 金属学报, 2019, 55(7): 811-820.
Zhengkai WU, Shengchuan WU, Jie ZHANG, Zhe SONG, Yanan HU, Guozheng KANG, Haiou ZHANG. Defect Induced Fatigue Behaviors of Selective Laser Melted Ti-6Al-4V via Synchrotron Radiation X-Ray Tomography. Acta Metall Sin, 2019, 55(7): 811-820.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2018.00408      或      https://www.ams.org.cn/CN/Y2019/V55/I7/811

图1  试样成形及制备位置示意图
图2  高周疲劳试样尺寸图
图3  同步辐射X射线原位成像实验工作原理及原位成像疲劳试样尺寸示意图
图4  X射线原位成像疲劳试样缺陷三维重构结果
图5  缺陷等效直径的频率直方图及累积频率曲线
图6  缺陷球度的频率直方图及正态分布拟合曲线
图7  不同等效直径缺陷的形貌表征
图8  X射线成像试样裂纹三维形貌重构结果及相应断口形貌
图9  选区激光熔化Ti-6Al-4V合金高周疲劳试样疲劳断口形貌
图10  选区激光熔化Ti-6Al-4V合金不同类型缺陷断口形貌特征
图11  缺陷位置表征示意图
图12  选区激光熔化Ti-6Al-4V合金高周疲劳试样裂纹源缺陷与疲劳寿命的关系
图13  作图求极值统计方法所需尺寸参数(α)和位置参数(λ)
图14  一定体积下最大缺陷特征尺寸的估算曲线
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