On the role of Re in the stress and temperature dependence of creep of Ni-base single crystal superalloys
On the role of Re in the stress and temperature dependence of creep of Ni-base single crystal superalloys
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DOI：
10.1016/j.msea.2015.01.010
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发表时间：
2015-03
期刊：
影响因子：
6.4
通讯作者：
P. Wollgramm;H. Buck;K. Neuking;A. Parsa;S. Schuwalow;J. Rogal;R. Drautz;G. Eggeler
中科院分区：
文献类型：
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作者：
P. Wollgramm;H. Buck;K. Neuking;A. Parsa;S. Schuwalow;J. Rogal;R. Drautz;G. Eggeler
本文研究了一种镍基单晶高温合金的蠕变行为。我们评估了最小蠕变速率的应力和温度依赖关系，结果显示幂律型的应力依赖关系（以应力指数n为特征）和指数型的温度依赖关系（以表观活化能Q app为特征）。在高温（1323 K）和低应力（160 MPa）蠕变条件下，n和Q分别为5.3和529 kJ/mol。在较低温度（1123 K）和较高应力（600 MPa）条件下，应力指数n较高（8.5），蠕变表观活化能较低（382 kJ/mol）。结果表明：应力指数n随应力的增加和温度的降低而增大，而表观活化能随应力的降低和温度的升高而增大。利用密度泛函理论（DFT）计算了稀土在低重浓度镍-稀土二元合金中的扩散活化能。所得能量几乎比蠕变的表观活化能小1 / 2。我们解释了为什么仅仅根据一种合金元素的扩散来解释蠕变的温度依赖性是不直接的。我们表明微观结构的演变也必须考虑。
In the present study we investigate the creep behavior of a Ni-base single crystal superalloy. We evaluate the stress and temperature dependence of the minimum creep rate, which shows a power law type of stress dependence (characterized by a stress exponent n) and an exponential type of temperature dependence (characterized by an apparent activation energy Q app). Under conditions of high temperature (1323 K) and low stress (160 MPa) creep, n and Q app are determined as 5.3 and 529 kJ/mol, respectively. For lower temperatures (1123 K) and higher stresses (600 MPa) the stress exponent n is higher (8.5) while the apparent activation energy of creep is lower (382 kJ/mol). We show that there is a general trend: stress exponents n increase with increasing stress and decreasing temperature, while higher apparent activation energies are observed for lower stresses and higher temperatures. We use density functional theory (DFT) to calculate the activation energy of diffusion for Re in a binary Ni–Re alloy with low Re-concentrations. The resulting energy is almost a factor 2 smaller than the apparent activation energy of creep. We explain why it is not straightforward to rationalize the temperature dependence of creep merely on the basis of the diffusion of one alloying element. We show that the evolution of the microstructure also must be considered.