Fatigue behaviour and lifing of two single crystal superalloys
Fatigue behaviour and lifing of two single crystal superalloys
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DOI：
10.1046/j.1460-2695.2001.00392.x
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发表时间：
2001-08
影响因子：
3.7
通讯作者：
D. W. MacLachlan;D. Knowles
中科院分区：
文献类型：
--
作者：
D. W. MacLachlan;D. Knowles
建立了单晶高温合金RR 2000和CMSX-4在蠕变和疲劳条件下的高温循环寿命预测模型。一个组合的蠕变-疲劳模型被使用，虽然它被发现，故障总是发生蠕变或疲劳分别，蠕变-疲劳相互作用有很小的影响。本文介绍了一系列断续高、低频试验的微观结构研究，并结合一系列断续蠕变试验的结果，确定了蠕变和疲劳的独立和相互作用的机理。当存在蠕变损伤时，材料表现均匀。在这些条件下，裂纹扩展是初始控制的，失效机制是表面或铸孔引发的平面裂纹扩展，随后是晶面上的剪切。随着温度降低或循环频率增加，材料表现得不那么均匀，并且在循环期间形成剪切带。在这些条件下，裂纹的扩展再次受到初始控制，断裂是由晶体学裂纹沿着剪切带快速扩展引起的。这种失效是一种明显的疲劳失效，并且在几乎不存在蠕变损伤时发生。在某些循环条件下，主要是晶体学失效机制占主导地位的那些条件下，材料在高达约950 °C的温度下显示出抗疲劳性的异常增加，这种行为已经通过将其与应变速率和温度对材料屈服强度的影响相关联来量化。
A model has been developed to predict the high temperature cyclic life of single crystal superalloys RR2000 and CMSX-4 under conditions of creep and fatigue. A combined creep-fatigue model is used, although it is found that failure always occurs by creep or fatigue separately, and that creep-fatigue interaction has a minor influence. Microstructural investigation of a series of interrupted high- and low-frequency tests are presented, these are combined with the results of a series of interrupted creep tests to identify the separate and interactive mechanisms of creep and fatigue. When creep damage is present the material behaves homogeneously. Under these conditions crack growth is initiation controlled, the mechanism of failure is surface or casting pore-initiated planar crack growth followed by shear on crystallographic planes. As the temperature is lowered or the cyclic frequency increased, the material behaves less homogeneously and shear bands are formed during cycling. Crack growth under these conditions is again initiation controlled and failure is by rapid crystallographic crack growth along shear bands. Such a failure is a distinct fatigue failure and occurs when little creep damage is present. Under certain cyclic conditions, mainly those where the crystallographic failure mechanism is dominant, the material shows an anomalous increase in fatigue resistance with temperature up to approximately 950 °C, This behaviour has been quantified by relating it to the effect of strain rate and temperature on the yield strength of the material.