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金属学报  2015, Vol. 51 Issue (5): 569-579    DOI: 10.11900/0412.1961.2014.00447
  论文 本期目录 | 过刊浏览 |
冷坩埚定向凝固Ti-47Al-2Cr-2Nb合金的拉伸与高周疲劳性能研究*
丁宏升(),尚子博,王永喆,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
TENSILE AND HIGH CYCLE FATIGUE PROPERTIES OF Ti-47Al-2Cr-2Nb DIRECTIONALLY SOLIDIFIED BY COLD CRUCIBLE METHOD
Hongsheng DING(),Zibo SHANG,Yongzhe WANG,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
引用本文:

丁宏升, 尚子博, 王永喆, 陈瑞润, 郭景杰, 傅恒志. 冷坩埚定向凝固Ti-47Al-2Cr-2Nb合金的拉伸与高周疲劳性能研究*[J]. 金属学报, 2015, 51(5): 569-579.
Hongsheng DING, Zibo SHANG, Yongzhe WANG, Ruirun CHEN, Jingjie GUO, Hengzhi FU. TENSILE AND HIGH CYCLE FATIGUE PROPERTIES OF Ti-47Al-2Cr-2Nb DIRECTIONALLY SOLIDIFIED BY COLD CRUCIBLE METHOD[J]. Acta Metall Sin, 2015, 51(5): 569-579.

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摘要: 

采用冷坩埚定向凝固技术制备了定向柱状晶的Ti-47Al-2Cr-2Nb合金铸锭, 在改变抽拉速率的情况下, 所获得的铸锭具有不同片层间距的全片层组织. 通过拉伸性能实验, 测得其室温极限抗拉强度最高达到652 MPa, 伸长率最大达到1.5%, 而高温极限抗拉强度最高达到490 MPa, 伸长率最大达到5.0%. 通过高周疲劳性能实验, 绘制了抽拉速率分别为1.0和1.2 mm/min时定向凝固合金的应力-循环次数(S-N)曲线以及应力比R为0.1时的疲劳极限值. 对比断口形貌分析表明, 室温时试样拉伸断裂方式为脆性断裂, 而经高周疲劳实验后断裂方式为脆性解理断裂; 高温时试样拉伸断裂方式则为大部分脆性断裂与少部分延性断裂并存. 对高周疲劳试样断口的分析表明, 疲劳裂纹在相界面和B2相附近萌生, 据此基于塑性钝化理论分析了其裂纹扩展机制, 并绘制了高周疲劳裂纹扩展模式图.

关键词 Ti-47Al-2Cr-2Nb合金定向凝固冷坩埚拉伸性能高周疲劳    
Abstract

TiAl-based alloys have recently received considerable attention as one of the promising candidates for application in aero engine blades by replacing the Ni-based superalloys because of their unique properties, such as high specific strength, high specific stiffness and good oxidation resistance. However, there are some shortcomings limiting the application of TiAl-based alloys, namely, their brittleness and poor processing properties. Nevertheless, aero engine blades usually suffer a variety of cyclic loadings during the period of services, which finally results in fatigue failure. According to statistics, fatigue failure, mainly high cycle fatigue (HCF), occupies almost 80% failure modes of gas turbine blades in aero engines. Consequently, more and more researches about fatigue behavior of blade materials have been done in the last tens of years. However, there are less relevant results about TiAl-based alloys, especially HCF properties. Recently, the advancement of directional solidification (DS) of TiAl-based alloys using cold crucible has revealed that the ductility can be enhanced at room and elevated temperature. For purpose to verify the influence of DS structures on the tensile and HCF properties, TiAl-based alloy in composition with Ti-47Al-2Cr-2Nb (atomic fraction, %) was prepared and evaluated in this work. Directionally solidified Ti-47Al-2Cr-2Nb alloy ingots with different withdrawal rates (1.0, 1.2 and 1.4 mm/min) were prepared by cold crucible method under alter electromagnetic field in a vacuum furnace. Based on these ingots, macro and microstructures have been characterized by methods of digital camera, OM, SEM and XRD. Furthermore, the tensile properties at room and high temperature (800 ℃) as well as HCF properties at room temperature have been measured respectively. So, the relationship between microstructures and mechanical properties of TiAl-based alloy, especially HCF properties, was demonstrated reasonably and mechanism in which HCF cracks propagated was discussed. The results show that the comprehensive mechanical properties of Ti-47Al-2Cr-2Nb alloy can be significantly improved after directionally solidified using cold crucible. The tensile strength reaches 652 MPa at room temperature with the maximum elongation of 1.5%. Meanwhile, the tensile strength at 800 ℃ attains 490 MPa with the elongation of 5.0%. Based on the data of HCF test at room temperature with the stress ratio of 0.1, the equations of stress amplitude-number of cycles to failure (S-N) curve at different withdrawal rates are calculated. The fatigue limits are 300 and 247 MPa with the withdrawal rates of 1.0 and 1.2 mm/min, respectively, namely, with the increase of withdrawal rate, the fatigue fracture resistance decreases. The mode of HCF fracture of directionally solidified Ti-47Al-2Cr-2Nb alloy behaves in brittle cleavage fracture. And micro-cracks which can propagate along and perpendicular to the lamellae at the same time are observed between α2/g lamellae and around B2 phases.

Key wordsTi-47Al-2Cr-2Nb alloy    directional solidification    cold crucible    tensile property    high cycle fatigue
收稿日期: 2014-08-09     
基金资助:*国家自然科学基金项目51171053和51471062及国家重点基础研究发展计划项目2011CB605504资助
Withdrawal rate v mm/min Power kW Ingot length mm Dummy height (initiation/end) mm Primer height (initiation/end) mm Feeding length mm
1.0 49 110.3 56/51 84/80 228.5
1.2 49 114.0 56/60 84/88 234.1
1.2 49 109.8 56/57 84/87 224.8
1.2 49 110.1 56/64 84/86 231.5
1.2 49 110.0 56/52 84/82 228.1
1.4 49 99.6 56/50 84/82 202.8
表1  Ti-47Al-2Cr-2Nb合金的定向凝固工艺参数
图1  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金的宏观组织
图2  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金稳定生长区片层组织的BSE像
图3  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金稳定生长区横截面的宏观组织
v / (mm·min-1) D / mm q / (°) l / mm
1.0 251 36.4 1.81
1.2 198 49.3 1.42
1.4 135 67.2 1.16
表2  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金的晶粒大小(D)、片层取向(q)和片层间距(l)
图4  抽拉速率为1.2 mm/min时定向凝固Ti-47Al-2Cr-2Nb合金中不同凝固区域的XRD谱
图5  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金的室温拉伸应力-应变曲线
图6  抽拉速率为1.2 mm/min时定向凝固Ti-47Al-2Cr-2Nb合金的室温拉伸断口形貌
图7  不同抽拉速率下定向凝固Ti-47Al-2Cr-2Nb合金的高温(800 ℃)拉伸应力-应变曲线
图8  抽拉速率为1.2 mm/min时定向凝固Ti-47Al-2Cr-2Nb合金的高温(800 ℃)拉伸断口形貌
图9  定向凝固Ti-47Al-2Cr-2Nb合金高周疲劳断裂后的形貌
图10  定向凝固Ti-47Al-2Cr-2Nb合金的应力-循环次数(S-N)曲线
图11  定向凝固Ti-47Al-2Cr-2Nb合金的衍生应力-循环次数曲线
图12  抽拉速率为1.2 mm/min时定向凝固Ti-47Al-2Cr-2Nb合金的高周疲劳断口形貌
图13  抽拉速率为1.0 mm/min时定向凝固Ti-47Al-2Cr-2Nb合金高周疲劳未断裂试样的宏观形貌及其不同部位的BSE像
图14  定向凝固Ti-47Al-2Cr-2Nb合金的疲劳裂纹扩展模式示意图
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