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首页> 外文会议>Proceeding of An International Conference the Importance of understanding the fundamentals of the fatigue Process in Counteracting Its Effects in Engineering Components and Structures,and to Reflect on the Contributions of K.J.Miller Sheffield/United >High temperature fatigue of Ni-base superalloys:Microstructural and environmental effects
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High temperature fatigue of Ni-base superalloys:Microstructural and environmental effects

机译：镍基高温合金的高温疲劳：组织和环境影响

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摘要

The effects of environment and metallurgical factors on the fatigue crack growth rate (FCGR) behaviour of Ni-based superalloys are analysed in two alloys,Inconel 718 and Alloy N18 used for the fabrication of turbine discs.Inconel 718 is a widely used wrought alloy,while Alloy N18 is representative of the most advanced PM superalloys.It is shown that the FCGR behaviour of these materials is largely dependent on microstructural parameters,including gamma recipitate size,grain size,and grain morphology.It is also confirmed that the FCGRs of these alloys tested at elevated temperature ( approx approx 650 deg C) and low frequency,in particular in fatigue with a tensile hold time,are largely dependent on oxygen partial pressure,PO_2.In both materials a transition in FCGRs is observed when PO_2 is reduced below 10~-3 mbar.This transition is related to the types of oxides formed ahead of the crack tip: spinel type above the transition and Cr_2O_3 type below the transition.In both alloys two extreme regimes for the FCGR behaviour are distinguished:(i) a pure cycle-dependent regime,and (ii) a pure time-dependent regime.These regimes are associated with widely different fracture modes: transgranular in the former case,intergranular in the latter.An attempt is made to give guidelines for modelling the FCGR behaviour in both regimes.
机译：分析了环境和冶金因素对镍基高温合金疲劳裂纹扩展速率（FCGR）行为的影响，分析了两种合金，即用于制造涡轮盘的Inconel 718和N18合金.Inconel 718是一种广泛使用的锻造合金， N18合金是最先进的PM超级合金的代表。研究表明，这些材料的FCGR行为在很大程度上取决于微观结构参数，包括γ沉淀物尺寸，晶粒尺寸和晶粒形态。还证实了这些材料的FCGR在高温（大约650摄氏度）和低频下（尤其是在具有拉伸保持时间的疲劳中）进行测试的合金很大程度上取决于氧分压PO_2。在两种材料中，当PO_2降至以下时，均会观察到FCGR的转变10〜-3 mbar。此过渡与裂纹尖端之前形成的氧化物类型有关：过渡以上为尖晶石型，过渡以下为Cr_2O_3型两种合金FCGR行为的极端机制有以下几种：（i）纯粹的循环依赖机制和（ii）纯粹的时间依赖机制。这些机制与广泛不同的断裂模式有关：前者为穿晶型，后者为粒间型试图给出在两种情况下模拟FCGR行为的指南。

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