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首页> 外文会议>ASME(American Society of Mechanical Engineers) Turbo Expo vol.4; 20060506-11; Barcelona(ES) >BIAXIAL THERMO MECHANICAL FATIGUE LIFE PROPERTY OF A Ni BASE DS SUPER ALLOY
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BIAXIAL THERMO MECHANICAL FATIGUE LIFE PROPERTY OF A Ni BASE DS SUPER ALLOY

机译：Ni基DS超级合金的双轴热机械疲劳寿命

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Development of life assessment methods of high temperature components in gas turbine for maintenance and operating cost reduction is strongly demanded by Japanese utilities. Especially, first row blades are subjected to complicated Thermo-Mechanical-Fatigue (TMF) loading during start-steady state-stop cycles. Therefore it is important to clarify the TMF life property of blade materials to develop a life assessment procedure. In this study, tension-torsion biaxial TMF tests have been performed between 450C and 870C on a Ni base directional solidified (DS) supper alloy. Strain ratio, φ was defined as shear strain range, Δγ, to normal strain range, Δε, and φ varied from 0 to infinite. The "Blade waveform" which simulated surface temperature and strain loading condition of the blade, was employed. The biaxial TMF tests were also carried out on coated specimens with CoCrAlY. Fatigue life under biaxial TMF loading showed strain ratio dependency giving shorter life with increasing φ. Considering biaxial stress effect on failure life, an equivalent shear strain range was derived based on Γ -plane theory, and biaxial TMF life was well correlated with the equivalent shear strain range. The biaxial TMF life was reduced by introducing strain hold duration at the maximum temperature. The maximum stress increased by introducing the hold time due to increasing mean stress level in the Blade waveform. It was concluded that creep damage gradually accumulated during cycles resulting in TMF life reduction. The nonlinear creep-fatigue damage accumulation model was applied to predict failure life of the hold time tests. As a result, failure life could be predicted within factor of 1.5 on observed life. It was found that fatigue life of CoCrAlY coated material reduced 1/2 to 1/3 from that of without coated material. From observation of longitudinal section of the coated specimens, many cracks started from coating surface and penetrated into the substrate. It was concluded that CoCrAlY coating reduced the biaxial TMF life due to acceleration of crack initiation period in the substrate.
机译：日本公用事业强烈要求开发燃气轮机中高温部件的寿命评估方法，以降低维护成本和运营成本。特别是，第一排叶片在启动-稳定状态-停止-循环期间会经受复杂的热机械疲劳（TMF）负载。因此，阐明叶片材料的TMF寿命特性对于制定寿命评估程序非常重要。在这项研究中，已经在450℃和870℃之间对Ni基定向凝固（DS）超级合金进行了拉伸-扭转双轴TMF测试。应变比φ定义为剪切应变范围Δγ至正常应变范围Δε，并且φ从0到无穷大。使用模拟叶片的表面温度和应变加载条件的“叶片波形”。还使用CoCrAlY在涂层样品上进行了双轴TMF测试。双轴TMF加载下的疲劳寿命显示出应变比依赖性，随着φ的增加，寿命缩短。考虑到双轴应力对破坏寿命的影响，基于Γ平面理论推导了等效剪切应变范围，而双轴TMF寿命与等效剪切应变范围相关性很好。通过在最高温度下引入应变保持时间，可以缩短双轴TMF寿命。由于增加了叶片波形中的平均应力水平，因此引入了保持时间，从而使最大应力增加。结论是蠕变损伤在循环过程中逐渐积累，导致TMF寿命缩短。应用非线性蠕变疲劳损伤累积模型来预测保持时间测试的失效寿命。结果，可以将失效寿命预测为观察寿命的1.5倍。已经发现，CoCrAlY涂层材料的疲劳寿命比没有涂层材料的疲劳寿命降低了1/2到1/3。从涂覆样品的纵向截面观察，许多裂纹从涂层表面开始并渗透到基底中。结论是，CoCrAlY涂层由于加速了基板中的裂纹萌生期而降低了双轴TMF寿命。

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