【作者】 张勇；

【导师】 陈刚；

【作者基本信息】 天津大学 ， 化工过程机械， 2016， 硕士

【摘要】 本文围绕镍基时效强化高温合金GH4169开展了一系列高温650oC下的试验研究,主要包括高温静置氧化试验、高温低周疲劳试验和高温蠕变-疲劳交互试验。高温静置氧化试验旨在通过研究该合金在650oC不同暴露时间条件下表面微观组织演化情况,揭示其高温氧化行为;高温低周疲劳试验采用应变控制循环对称加载,研究该合金高温低周疲劳性能;高温蠕变-疲劳交互试验在低周疲劳试验的基础上,在应变峰值处引入不同保持时间以研究该合金高温蠕变与疲劳的交互行为。此外,借助扫描电子显微镜对低周疲劳和蠕变-疲劳交互试验试样表面和断口进行了观察,分析该合金疲劳断裂形式和裂纹扩展模式以揭示微观失效机制。通过对试验结果分析整理可以得到以下结论:(1)GH4169合金在高温650oC时表面会发生氧化,随着高温静置时间增长氧化水平升高,主要表现在金属间化合物的氧化、开裂和脱落;(2)随着应变幅值增大,GH4169合金的高温低周疲劳寿命显著下降,除了较低应变幅0.3%该合金均呈现循环软化特性,且软化水平随应变幅值增大而增大;(3)对于高温蠕变-疲劳交互试验,保持时间的引入进一步削减合金低周疲劳寿命,而随保持时间延长该影响出现了“饱和”效应,此外保持时间并未改变合金循环软化特性;(4)低周疲劳断裂呈现脆性断裂特征,裂纹源均位于试样表面,二次裂纹和疲劳辉纹是主要的裂纹扩展模式;(5)随着保持时间的增长,GH4169合金的断口形貌由单一起裂变为多点起裂,裂纹扩展由穿晶扩展向沿晶扩展过渡。更多还原

【Abstract】 A series of tests have been conducted on a nickel based superalloy of GH4169 at elevated temperature of 650 oC,including high temperature oxidation tests,low cycle fatigue tests and creep-fatigue interaction tests.In order to release the superalloy’s oxidation behavior,high temperature oxidation tests were to study the micro change of the surface under different exposure times.Applying strain as control parameter,lo w cycle fatigue tests were to know about the superalloy’s low cycle fatigue performance.Importing hold period at peak strain,creep-fatigue tests were to study the creep-fatigue interaction behavior of GH4169.Furthermore,the surface and fracture surface of failure samples were observed by scanning electron microscope to analyze the fracture behavior and failure mechanism.The conclusions can be drawn as follows:(1)The oxidation level of GH4169 increases as the increasing high temperature exposure time,manifesting by the oxidation,cracking and flaking of intermetallic compounds.(2)Low cycle fatigue life decreases as the increasing strain amplitude.Besides it shows cyclic softening except for the low strain amplitude of 0.3% and the level of softening increases as the strain amplitude increases.(3)The introduction of hold period decreases fatigue life and before reaching saturation this effect becomes heavier as the elongation of hold period.In addition,the introduction of hold period didn ’t change the cyclic softening phenomenon of GH4169.(4)Low cycle fatigue showed brittle fracture,which all initiated from surface of samples.Secondary crack and fatigue striation were the main crack propagation mode.(5)As the increasing of hold period,c rack initiation transformed from single initiation site to multiple sites and the crack propagation changed from transgranular mode to intergranular mode.更多还原