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1、 国内图书分类号 TG115 53 国际图书分类号 620 171 3 工学硕士学位论文 TC4合金低温拉伸和低温真空疲劳性能研究 硕 士 研 究 生 张利清 导师 董尚利副研究员 申请学位级别 工学硕士 学 科 专 业 材料学 所 在 单 位 材料学院 答 辩 日 期 2007 年 7 月 授予学位单位 哈尔滨工业大学 Classified Index TG115 53 U D C 620 171 3 Dissertation for the Master Degree in Engineering A STUDY ON TENSILE AND VACUUM FATIGUE OF A TC4
2、 ALLOY AT CRYOGENIC TEMPERATURE Candidate Zhang Li Qing Supervisor Associate Prof Dong Shang Li Academic Degree Applied for Master of Engineering Specialty Material Science Affiliation School of Material Science and Engineering Date of Defence July 2007 Degree conferring Institution Harbin Institute
3、 of Technology 哈尔滨工业大学工学硕士学位论文 摘 要 本文采用MTS万能材料试验机 低温真空疲劳试验机 金相显微镜 扫描电镜 SEM 和透射电镜 TEM 研究了经 720 1h 退火处理TC4 合金的 低温 100 150 195 拉伸性能和室温大气 室温真空 10 3Pa 低 温真空 190 10 4Pa 条件下的疲劳性能及其变形断裂行为 同时考察了 Co60 辐照对TC4 合金室温和低温拉伸性能的影响 研究结果表明 TC4 合金经 720 1h 退火后呈现典型的 双相混合 组织特征 表现出优异的室温和低温拉伸性能 在 20 和 195 其抗拉 强度与延伸率分别为 1018
4、4MPa 14 8 和 1524 1MPa 14 5 随拉伸温度 的降低 TC4 合金的抗拉强度和屈服强度单调增加 延伸率缓慢下降 但 温度降至 195 时 延伸率又略有上升 经 Co60 辐照后 TC4 合金拉伸性 能变化不显著 室温强度下降 20MPa 30MPa 延伸率下降 1 SEM 观察 表明 TC4 合金在不同温度下的拉伸断口为韧窝断口 随拉伸温度的降 低 韧窝大小分布不均匀程度略有增加 TEM 分析表明 退火态 TC4 合金 在室温和低温的变形机制均以位错滑移为主 TC4 合金在室温大气 室温真空 10 3Pa 和低温真空 190 10 4Pa 三种 环境中的疲劳性能明显不同 低
5、温真空环境的最佳 室温大气环境的最差 真空环境的介于两者之间 TC4 合金在室温真空环境 10 3Pa 中的疲劳寿命 为室温大气环境中的两倍左右 而低温真空环境 190 10 4Pa 的疲劳寿命 则大幅度提高 表明温度对TC4 合金疲劳寿命的影响远远大于真空 SEM 观察表明 TC4 合金室温和低温真空疲劳断口可明显区分出裂纹萌生区 扩展区和瞬断区 裂纹萌生于试样表面 瞬断区存在大量韧窝 真空环境 中 由于钛合金的热传导较差 因循环应力产生的大量热量又不能传递到周 围环境中 疲劳断口有熔断现象 而在室温大气和低温真空环境中 没有出 现熔断现象 透射电镜 TEM 分析表明 在室温大气和低温真空环
6、境 190 10 4Pa 中 疲劳变形仍以位错滑移为主 关键词 TC4 合金 疲劳 拉伸性能 低温 真空 I 哈尔滨工业大学工学硕士学位论文 Abstract Tensile and vacuum fatigue properties and deformation fracture behavior at cryogenic temperature of a 720 1h annealed TC4 alloy have been studied by means of universal material testing system MTS fatigue testing machine
7、optical microscope scanning election microscope SEM and transmission electron microscope TEM Influence of Co60 irradiation on tensile properties of TC4 alloy has also been investigated The cryogenic tensile test was carried out at 100 150 and 195 while the fatigue test was performed in laboratory ai
8、r in vacuum 10 3Pa and in cryogenic temperature vacuum 195 10 4Pa respectively The results show that the 720 1h annealed TC4 alloy possesses an bimodal microstructure and exhibits excellent tensile properties with an UTS and elongation of 1018 4MPa and 14 8 at room temperature and 1524 1MPa and 14 5
9、 at 195 respectively The UTS and yield strength of TC4 alloy were found to monotonously increase while the elongation slowly decreases with decreasing the testing temperature and the elongation shows slightly increasing at 195 The Co60 irradiation has a little effect on tensile properties of TC4 all
10、oy resulting in a reduction of 20 30MPa in UTS and 1 decrease in elongation at room temperature SEM observations indicated that the fractured surfaces of TC4 alloy tested at room and cryogenic temperatures displayed dimple fracture features and the uniformity of dimples size distribution decreased w
11、ith decreasing the testing temperature TEM examinations showed that the dominant deformation mechanism of TC4 alloy tensioned at room and cryogenic temperatures would be dislocation slip The fatigue property of the annealed TC4 alloy was apparently different as tested in the three environments of la
12、boratory air vacuum 10 3Pa and cryogenic temperature vacuum 190 10 4Pa and the highest fatigue life could be obtained in the cryogenic temperature vacuum while the lowest one in the laboratory air It has been found that the fatigue life of TC4 alloy in vacuum is about two times of that in laboratory
13、 air and the fatigue life in cryogenic temperature vacuum increases obviously indicating the effect of temperature on II 哈尔滨工业大学工学硕士学位论文 fatigue life is greater than that of vacuum SEM observations showed that the crack initiation site crack prorogation path and rapid failure zone were distinguishab
14、le on the fractured surfaces of the specimens fatigued in laboratory air and cryogenic temperature vacuum The crack initiated at surface of the fatigue specimens and a lot of dimples could be found on the rapid failure zone Some melted zone could be observed on the fractured surface of specimens tes
15、ted in vacuum because of the low thermal conductivity of titanium alloy which leading to the generation of heat produced by cyclic stressing No such features could be found in the specimens tested in air or in vacuum at cryogenic temperature TEM examinations showed that dislocation slip is the main
16、deformation mode of the TC4 alloy fatigued in laboratory air or in the cryogenic temperature vacuum Keywords TC4 alloy fatigue tensile property cryogenic temperature vacuum III 哈尔滨工业大学工学硕士学位论文 目目 录 摘 要 I Abstract II 第 1 章 绪论 1 1 1 选题背景 1 1 2 钛合金 2 1 2 1 钛 2 1 2 2 钛合金的分类及性能特点 2 1 2 3 TC4 合金的热处理 3 1 2 4 TC4 合金的显微组织特征 4 1 3 疲劳机制 5 1 3 1 疲劳的概念 5 1 3 2 疲劳的分类 5 1 3 3 疲劳破坏机理 5 1 4 钛合金的疲劳 10 1 4 1 纯钛的疲劳 10 1 4 2 钛合金的疲劳 10 1 4 3 低温真空对疲劳性能的影响 14 1 5 本课题的研究目的及内容 15 第 2 章 试验材料及方法 17 2 1 试验材料及热处理工艺选择 17 2 1
