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arXiv 1601.06015cond-mat.mtrl-sci
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难熔高熵合金的相稳定性、局部化学无序及其对力学性能的影响

Phase stability, local chemical disorder and its effect on the mechanical properties of refractory high-entropy alloys

Soumyadipta Maiti, Walter Steurer

摘要:

本文研究了等原子态TaNbHfZr和TaNbHfZrTi高熵合金的相稳定性、短程簇集(SRC)型化学有序化、其它结构现象以及对强化的影响。从头计算已经完成,以确定热力学稳定性参数。铸态结构不包含任何局部化学有序,但高分辨透射电子显微镜(HRTEM)研究显示其局部畸变的晶格。通过从单晶X射线衍射(XRD)和粉末中子衍射(ND)研究中细化原子位移参数(ADP)来量化在其铸态和退火状态下的平均结构的局部晶格畸变。ADP的静态分量似乎占主导地位的热ADP,这表明在HEAs的局部晶格畸变的程度很高。晶格畸变导致固溶体状强化,与混合规则相比,这使HEAs的硬度增加了2-3倍。在退火HEA中形成的SRC具有垂直于方向的平面轮廓<1 0 0>。SRCs主要是Zr和Hf的共簇。SRC具有更高的原子体积,导致局部四方晶格畸变,这在XRD数据集和HRTEM晶格图像的快速傅里叶变换(FFT)中产生弥散条纹状强度。SRC的存在局部地降低了结构的晶格势能,并对位错的运动设置了额外的能垒。这增加了硬度,导致退火HEAs中约50%的额外强化。热力学分析表明,含有SRCs的弛豫结构降低了焓和构型熵。

英文摘要:

Equiatomic TaNbHfZr and TaNbHfZrTi high-entropy alloys (HEAs) have been investigated for their phase stability, short-range clustering (SRC) type chemical ordering, other structural phenomena and and the effects on strengthening. Ab-initio calculations have been done to determine the thermodynamic stability parameters. The as-cast structures do not contain any local chemical order, but the high-resolution transmission electron microscopy (HRTEM) studies reveal their locally distorted lattice. The local lattice distortion of the average structure in their as-cast and annealed state is quantified by refining atomic displacement parameters (ADPs) from single-crystal X-ray diffraction (XRD) and powder neutron diffraction (ND) studies. The static component of the ADPs appears to dominate over the thermal ADP, suggesting a high degree of local lattice distortion in the HEAs. The lattice distortions cause solid-solution like strengthening, which increases the hardness of the HEAs by a factor of 2-3 compared to the rule of mixture. The SRCs that form in the annealed HEAs have a planar profile perpendicular to the <1 0 0> directions. The SRCs mainly are co-clustering of Zr and Hf. The SRCs have a higher atomic volume causing local tetragonal lattice distortions, which in terms produce diffuse streak-like intensities in the XRD datasets and in the fast Fourier transform (FFT) of the HRTEM lattice images. The presence of SRCs locally reduces the lattice potential energy of the structure and puts additional energy barrier to the movement of dislocations. This increases the hardness causing around 50% of additional strengthening in the annealed HEAs. Thermodynamic analysis shows that the relaxed structure containing the SRCs lower the enthalpy and the configurational entropy.

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