一种镍基单晶超合金高温低周疲劳的晶体取向相关性模型

在950℃t对[001]、[012]、[112]、[011]和[114]晶体取向的镍基单晶超合金DD3试样进行了对称循环低周疲劳(ICF)试验。应变率取1.0×10-2,1.33×10-3,0.33×10-3s-1.试验结果表明,LCF特性显着地取决于晶体取向和应变率。试样断口细观分析表明,除了[001]取向试样外,其余所有试样断口上均有明显的等间距疲劳纹。这些疲劳纹由微裂纹组成,其间距取决于试样的晶体取向和总应变范围。基于晶体滑移理论,建立了疲劳纹间距和总分切应变范围及取向和应变率函数的一个简单关系。对Lall-Chin-Pope(LCP)模型进行修正并推广应用于循环塑性和疲劳寿命研究,提出了一个晶体取向和应变率参数,该参数可以很好地描述镍基单晶超合金高温低周疲劳循环塑性和疲劳寿命的晶体取向和应变率相关性。

A Crystallographic Model for the Orientation Dependence of Low Cyclic Fatigue Property of a Nickel-Base Single Crystal Superalloy

Fully reversed low cyclic fatigue(LCF) tests were conducted on [001],[012],[112],[011] and [11 4] oriented single crystals of nickel-based superalloy DD3 with different cyclic strain rates at 950℃.The cyclic strain rates were chosen as 1.0×10-2,1.33×10-3 and 0.33×10-3s-1.The octahedral slip systems were confirmed to be activated on all the specimens.The experimental result shows that the fatigue behavior depends on the crystallographic orientation and cyclic strain rate.Except [001] orientation specimens,it is found from the scanning electron microscopy(SEM) examination that there are typical fatigue striations on the fracture surfaces.These fatigue striations are made up of cracks.The width of the fatigue striations depends on the crystallographic orientation and varies with the total strain range.A simple linear relationship exists between the width and total shear strain range modified by an orientation and strain rate parameter.The nonconformity to the Schmid law of tensile/compressive flow stress and plastic behavior existed at 950℃,and an orientation and strain rate modified Lall-Chin-Pope(LCP) model was derived for the nonconformity.The influence of crystallographic orientation and cyclic strain rate on the LCF behavior can be predicted satisfactorily by the model.In terms of an orientation and strain rate modified total strain range,a model for fatigue life was proposed and used successfully to correlate the fatigue lives studied