通过相场模型系统研究了Fe-Cu-Mn-Ni合金成分、热处理温度及外部加载对α→γ相变行为的影响机制,并重点考察了体系成分、α/γ两相结构瞬时分布及二者随时间的演化规律.研究结果表明:较低含量的Cu元素,能促使该Fe基合金形成颗粒中心区域Cu富集但结构仍保持与母相(bcc结构)一致α的析出相;较高含量的Cu元素,则倾向于使其形成颗粒边缘区域Cu富集但为fcc的γ析出相.在Fe-Cu合金中添加少量Mn、Ni元素可以形成Mn/Ni成分环状富集的析出相结构,而增加Mn、Ni元素的含量会加速相变过程的发生,且Mn的促进作用大于Ni.通过改变热加工参数及外加载荷可以调控Fe基合金α+γ的两相微结构.时效温度越低或冷却速率越快,相变起始点越早,且随着相变的进行和析出相的增大,会出现Cu元素外排至边缘的现象;同时,外加载荷的增加也促使Cu富集γ相的形成.该研究结果为优化Fe-Cu-Mn-Ni合金性能提供了理论支持,并可对其他多元合金体系的相场模型研究提供参考.
In this study, the effects of alloy composition, heat treatment temperature, and external loading on the α → γ phase transformation behavior in Fe-Cu-Mn-Ni alloys were systematically investigated. Using a phase-field modeling approach, the composition and structural distributions of both α and γ phases were examined and analyzed, represented by two sets of order parameters. The results indicate that a lower Cu concentration promotes the formation of α precipitates with Cu enrichment at the particle center, maintaining the same crystal structure as the parent α phase（i.e., the bcc structure）. In contrast, a higher Cu concentration favors the formation of γ precipitates, characterized by Cu enrichment at the particle edge and an fcc crystal structure. Moreover, the addition of small amounts of Mn and Ni to Fe-Cu alloys leads to the formation of precipitate phases with Mn/Ni compositional ring enrichment. Increasing the Mn and Ni content accelerates the phase transformation process, with Mn exhibiting a more pronounced effect than Ni. Furthermore, the α + γ dual-phase microstructure of Fe-based alloys can be regulated by adjusting the thermomechanical parameters and external loading. A lower aging temperature or a faster cooling rate results in earlier initiation of the phase transformation, as well as earlier Cu enrichment at the particle edges during precipitate growth. Additionally, increasing external loading promotes the formation of Cu-enriched γ phases. These findings provide theoretical support for optimizing the performance of Fe-Cu-Mn-Ni alloys and offer a reference for phase-field modeling studies on other multicomponent alloy systems.
[1] Alami A H, Hawili A A. Synthesis, characterization and applications of FeCu alloys[J]. Applied Surface Science Advances, 2020, 1:10027.
[2] Shi J J, Zhao W Z, Wu Y C, et al. Evolution of microstructures and hardening property of initial irradiated, post-irradiation annealed and re-irradiated Chinese-type low-Cu reactor pressure vessel steel[J]. Journal of Nuclear Materials, 2019, 523:333-341.
[3] Sun Y, Zhao Y, Zhao B, et al. Multi-component phase-fleld simulation of microstructural evolution and elemental distribution in Fe-Cu-Mn-Ni-Al alloy[J]. Calphad, 2020, 69:101759.
[4] Odette G R, Lucas G E. Recent progress in understanding reactor pressure vessel steel embrittlement[J]. Radiation Efiects and Defects in Solids, 1998, 144(1/2/3/4):189-231.
[5] Seko A, Odagaki N, Nishitani S R, et al. Free-energy calculation of precipitate nucleation in an Fe-Cu-Ni alloy[J]. Materials Transactions, 2004, 45(7):1978-1981.
[6] Goodman S R, Brenner S S, Low J R. An FIM-atom probe study of the precipitation of copper from lron-1.4 at. pct copper. Part I:Field-ion microscopy[J]. Metallurgical Transactions, 1973, 4(10):2363-2369.
[7] Habibi-Bajguirani H R, Jenkins M L J P M L. High-resolution electron microscopy analysis of the structure of copper precipitates in a martensitic stainless steel of type. PH 15-5[J]. Philosophical Magazine Letters, 1996, 73(4):155-162.
[8] Koyama T, Onodera H. Computer simulation of phase decomposition in Fe-Cu-Mn-Ni quaternary alloy based on the phase-fleld method[J]. Materials Transactions, 2005, 46(6):1187-1192.
[9] Isheim D, Gagliano M S, Fine M E, et al. Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale[J]. Acta Materialia, 2006, 54(3):841-849.
[10] Sun Y Y, Zhao Y H, Zhao B J, et al. Phase-fleld modeling of microstructure evolution of Cu-rich phase in Fe-Cu-Mn-Ni-Al quinary system coupled with thermodynamic databases[J]. Journal of Materials Science, 2019, 54(16):11263-11278.
[11] Koyama T, Hashimoto K, Onodera H. Phase-fleld simulation of phase transformation in Fe-Cu-Mn-Ni quaternary alloy[J]. Materials Transactions, 2006, 47(11):2765-2772.
[12] Cahn J W, Hilliard J E. Free energy of a nonuniform system. I. Interfacial free energy[J]. The Journal of Chemical Physics, 1958, 28(2):258-267.
[13] Allen S M, Cahn J W. Ground state structures in ordered binary alloys with second neighbor interactions[J]. Acta Metallurgica, 1972, 20(3):423-433.
[14] Eisenlohr P, Diehl M, Lebensohn R A, et al. A spectral method solution to crystal elastoviscoplasticity at flnite strains[J]. International Journal of Plasticity, 2013, 46:37-53.
[15] Miller M K, Russell K F. Embrittlement of RPV steels:an atom probe tomography perspective[J]. Journal of Nuclear Materials, 2007, 371(1/2/3):145-160.
[16] Monzen R, Iguchi M, Jenkins M L. Structural changes of 9R copper precipitates in an aged Fe-Cu alloy[J]. Philosophical Magazine Letters, 2000, 80(3):137-148.
