Precipitates in Al-Cu alloys revisited: Atom-probe tomographic experiments and first-principles calculations of compositional evolution and interfacial segregation
Precipitates in Al-Cu alloys revisited: Atom-probe tomographic experiments and first-principles calculations of compositional evolution and interfacial segregation
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DOI：
10.1016/j.actamat.2011.06.036
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发表时间：
2011-09-01
期刊：
影响因子：
9.4
通讯作者：
Seidman, David N.
中科院分区：
文献类型：
--
作者：
Biswas, Aniruddha;Siegel, Donald J.;Seidman, David N.
采用原子探针层析、透射电子显微镜、X射线衍射和第一性原理计算研究了Al-1.7at.%中GPII区和θ '相的成分演化和α-Al/θ'界面的溶质偏析Cu（Al-4wt.% Cu）合金。在438 K时效8 h后观察到GPII区，而更高的时效温度，463 K时效8 h和533 K时效4 h，仅显示θ '沉淀。大多数GPII区和θ '沉淀物被证明是Cu不足，在较低的两个时效温度，只有533 K的处理导致θ'的化学计量与预期的Al 2Cu平衡组成一致。对于含有类似于200 at. ppm Si，我们发现Si分配到GPII区和θ '沉淀物的证据。在533 K下时效的共格α-Al/θ '界面处观察到显著的Si偏析，导致界面Si浓度比α-Al基体中的Si浓度大11倍以上。重要的是，随着时效温度从463 K增加到533 K，Si界面浓度经历了从非平衡离域分布到平衡局域分布的转变。与这些测量结果一致，第一性原理计算预测了一个强的热力学驱动力，有利于Si分区的Cu网站在θ '。硅在θ '沉淀物处的偏析和向θ'沉淀物的分配导致界面自由能的降低，并且伴随着成核电流的增加。我们的研究结果表明，Si催化这些合金中沉淀的早期阶段，与在商业Al-Cu-Si合金中观察到的较高的沉淀物数密度一致。(C)2011 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Atom-probe tomography, transmission electron microscopy, X-ray diffraction and first-principles calculations are employed to study: (i) compositional evolution of GPII zones and theta' precipitates; and (ii) solute segregation at alpha-Al/theta' interfaces in Al-1.7 at.% Cu (Al-4 wt.% Cu) alloys. GPII zones are observed after aging at 438 K for 8 h, whereas higher aging temperatures, 463 K for 8 h and 533 K for 4 h, reveal only theta' precipitates. Most GPII zones and theta' precipitates are demonstrated to be Cu-deficient at the lower two aging temperatures; only the 533 K treatment resulted in theta' stoichiometries consistent with the expected Al2Cu equilibrium composition. For alloys containing similar to 200 at. ppm Si we find evidence of Si partitioning to GPII zones and theta' precipitates. Significant Si segregation is observed at the coherent alpha-Al/theta' interface for aging at 533 K, resulting in an interfacial Si concentration more than 11 times greater than in the alpha-Al matrix. Importantly, the Si interfacial concentration undergoes a transition from a non-equilibrium delocalized profile to an equilibrium localized profile as the aging temperature is increased from 463 to 533 K. Consistent with these measurements, first-principles calculations predict a strong thermodynamic driving force favoring Si partitioning to Cu sites in theta'. Silicon segregation at, and partitioning to, theta' precipitates results in a decrease in interfacial free energy, and concomitantly an increase in the nucleation current. Our results suggest that Si catalyzes the early stages of precipitation in these alloys, consistent with the higher precipitate number densities observed in commercial Al-Cu-Si alloys. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.