B含量对K417G合金凝固过程中组织演变和力学性能的影响
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摘要
研究了B含量对K417G合金凝固过程中相析出以及铸态组织和力学性能的影响。研究不仅证实了B显著促进元素偏析以及凝固后期(γ+γ')共晶析出,还发现B对K417G合金凝固早期基体γ相的析出和长大具有明显影响。B降低基体γ相的析出温度,抑制γ相的形核,并阻碍γ相生长。当B含量低于0.036%时,由于B降低γ相形核率,导致K417G合金的晶粒组织随B含量增加明显粗化。当B含量增加至0.060%时,尽管B仍然降低γ相形核率,但由于其阻碍γ相枝晶的早期生长,使熔体内部过冷度升高,局部发生晶粒细化。B对K417G合金力学性能的影响决定于硼化物的晶界析出形态,当B含量低于0.036%时,硼化物以颗粒状在晶界析出并对晶界产生强化作用,合金的900℃拉伸性能和900℃、315 MPa持久性能随B含量的增加而显著提高。当B含量达到0.060%时,共晶态硼化物在(γ+γ')前沿析出,导致共晶态硼化物与(γ+γ')的界面显著弱化,拉伸和持久性能显著降低。
Boron is a key element in superalloys and many other metallic materials for strengthening the grain boundaries. However, it also has harmful effect on aggravating the solidification segregation of the alloys. Although the mechanism for the influences of B on the alloys has been studied extensively, it is still required to study in some alloys currently because the compositive effects of boron in different alloys are sometimes distinct. K417 G, a cast superalloy with good comprehensive properties, has been applied in aero engines of China. In the present work, the effects of boron content on the microstructure evolution during the solidification and the mechanical properties of the as cast K417 G alloy have been investigated, providing some fundamental information for the control of boron addition in the alloy. It has been found that boron aggravated the elemental segregation and promoted the eutectic(γ + γ') precipitation at the final stage of the solidification of K417 G alloy. In addition, boron decreased the precipitation temperature, and hence reduced the nucleation rate of the γ matrix. When the boron content was below 0.036%,the grain size was increased with the increment of B content, which is caused by the decreased nucleation of the γ phase. When the B addition was increased up to 0.060%, the grain was refined at some local places, because the growth of the dendrites was inhibited and the γ phase could nucleate at the inner part of the subcooled liquids. The mechanical properties of K417 G alloy were significantly influenced by the precipitation of the boride at the grain boundaries. The borides were precipitated as fine particles at the grain boundaries when the B addition was below 0.036%, and the tensile properties at 900 ℃ and the stress rupture properties at 900 ℃ and 315 MPa were markedly improved with the increasing B content in this addition range. When the B content was increased to 0.060%, the boride was precipitated as eutectic form in front of the eutectic(γ+γ'). The tensile and stress rupture properties were decreased due to the weak cohesion between the eutectic(γ+γ') and the eutectic form borides.
Boron is a key element in superalloys and many other metallic materials for strengthening the grain boundaries. However, it also has harmful effect on aggravating the solidification segregation of the alloys. Although the mechanism for the influences of B on the alloys has been studied extensively, it is still required to study in some alloys currently because the compositive effects of boron in different alloys are sometimes distinct. K417 G, a cast superalloy with good comprehensive properties, has been applied in aero engines of China. In the present work, the effects of boron content on the microstructure evolution during the solidification and the mechanical properties of the as cast K417 G alloy have been investigated, providing some fundamental information for the control of boron addition in the alloy. It has been found that boron aggravated the elemental segregation and promoted the eutectic(γ + γ') precipitation at the final stage of the solidification of K417 G alloy. In addition, boron decreased the precipitation temperature, and hence reduced the nucleation rate of the γ matrix. When the boron content was below 0.036%,the grain size was increased with the increment of B content, which is caused by the decreased nucleation of the γ phase. When the B addition was increased up to 0.060%, the grain was refined at some local places, because the growth of the dendrites was inhibited and the γ phase could nucleate at the inner part of the subcooled liquids. The mechanical properties of K417 G alloy were significantly influenced by the precipitation of the boride at the grain boundaries. The borides were precipitated as fine particles at the grain boundaries when the B addition was below 0.036%, and the tensile properties at 900 ℃ and the stress rupture properties at 900 ℃ and 315 MPa were markedly improved with the increasing B content in this addition range. When the B content was increased to 0.060%, the boride was precipitated as eutectic form in front of the eutectic(γ+γ'). The tensile and stress rupture properties were decreased due to the weak cohesion between the eutectic(γ+γ') and the eutectic form borides.
引文
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[16] Du B N, Sheng L Y, Lai C, et al. Evolution and structure characterization of the carbide and boride during creep in a Ni-based superalloy[J]. Rare Met. Mater. Eng., 2017, 46:2123(都贝宁,盛立远,赖琛等.一种镍基高温合金蠕变过程中碳、硼化物的演变行为及结构表征[J].稀有金属材料与工程, 2017,46:2123)
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[18] Zhang H W, Qin X Z, Li X W, et al. Incipient melting behavior and its influences on the mechanical properties of a directionally solidified Ni-based superalloy with high boron content[J]. Acta Metall. Sin., 2017, 53:684(张洪伟,秦学智,李小武等.一种高硼定向凝固合金的初熔行为及其对力学性能的影响[J].金属学报, 2017, 53:684)
[19] Du B N, Shi Z W, Yang J X, et al. M5B3boride at the grain boundary of a nickel-based superalloy[J]. J. Mater. Sci. Technol., 2016,32:265
[20] Wu B P, Li L H, Wu J T, et al. Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys[J]. Int. J. Miner. Metall. Mater., 2014, 21:1120
[21] Hu Z Q, Sun W R, Song H W. A new method for strengthening wrought superalloys-micro-alloying with phosphorus and boron[J]. Eng. Sci., 2005, 3(4):1
[22] Zhu Y X, Zhang S N, Zhang T X, et al. A new way to improve the superalloys[A]. Superalloys 1992[C]. Warrendale, PA:TMS,1992:145)
[23] High Temperature Material Branch of the Chinese Society for Metals. China Superalloys Handbook(Volume Two)[M]. Beijing:Standards Press of China, 2012:93(中国金属学会高温材料分会.中国高温合金手册,下卷[M].北京:中国标准出版社, 2012:93)
[2] Yan B C, Zhang J, Lou L H. Effect of boron additions on the microstructure and transverse properties of a directionally solidified superalloy[J]. Mater. Sci. Eng., 2008, A474:39
[3] Shulga A V. Boron and carbon behavior in the cast Ni-base superalloy EP962[J]. J. Alloys Compd., 2007, 436:155
[4] Zhao G D, Yu L X, Yang G L, et al. The role of boron in modifying the solidification and microstructure of nickel-base alloy U720Li[J]. J. Alloys Compd., 2016, 686:194
[5] Hu Q, Liu L, Zhao X B, et al. Effect of carbon and boron additions on segregation behavior of directionally solidified nickel-base superalloys with rhenium[J]. Trans. Nonferrous Met. Soc. China,2013, 23:3257
[6] Whitesell H S, Overfelt R A. Influence of solidification variables on the microstructure, macrosegregation, and porosity of directionally solidified Mar-M247[J]. Mater. Sci. Eng., 2001, A318:264
[7] Hong H U, Kim I S, Choi B G, et al. On the mechanism of serrated grain boundary formation in Ni-based superalloys with lowγ′volume fraction[A]. Superalloys 2012[C]. Hoboken, NJ:John Wiley&Sons, Inc., 2012:53
[8] Alam T, Felfer P J, Chaturvedi M, et al. Segregation of B, P, and C in the Ni-based superalloy, Inconel 718[J]. Metall. Mater. Trans.,2012, 43A:2183
[9] Zhang H R, Ojo O A. TEM analysis of Cr-Mo-W-B phase in a DS nickel based superalloy[J]. J. Mater. Sci., 2008, 43:6024
[10] Zhang H R, Ojo O A, Chaturvedi M C. Nanosize boride particles in heat-treated nickel base superalloys[J]. Scr. Mater., 2008,58:167
[11] Blavette D, Duval P, Letellier L, et al. Atomic-scale APFIM and TEM investigation of grain boundary microchemistry in Astroloy nickel base superalloys[J]. Acta Mater., 1996, 44:4995
[12] Yang F, Hou J S, Gao S, et al. The effects of boron addition on the microstructure stability and mechanical properties of a Ni-Cr based superalloy[J]. Mater. Sci. Eng., 2018, A715:126
[13] Hosseini S A, Abbasi S M, Madar K Z, et al. The effect of boron and zirconium on wrought structure andγ-γ'lattice misfit characterization in nickel-based superalloy ATI 718Plus[J]. Mater.Chem. Phys., 2018, 211:302
[14] Kontis P, Alabort E, Barba D, et al. On the role of boron on improving ductility in a new polycrystalline superalloy[J]. Acta Mater., 2017, 124:489
[15] Wang C S, Guo Y A, Guo J T, et al. Microstructural stability and mechanical properties of a boron modified Ni-Fe based superalloy for steam boiler applications[J]. Mater. Sci. Eng., 2015, A639:380
[16] Du B N, Sheng L Y, Lai C, et al. Evolution and structure characterization of the carbide and boride during creep in a Ni-based superalloy[J]. Rare Met. Mater. Eng., 2017, 46:2123(都贝宁,盛立远,赖琛等.一种镍基高温合金蠕变过程中碳、硼化物的演变行为及结构表征[J].稀有金属材料与工程, 2017,46:2123)
[17] Yu Z H, Zhang Y, Zhai Y N, et al. The research progress of the role of C, B and Hf in nickel-based superalloy[J]. Foundry, 2017, 66:1076(余竹焕,张洋,翟娅楠等. C、B、Hf在镍基高温合金中作用的研究进展[J].铸造, 2017, 66:1076)
[18] Zhang H W, Qin X Z, Li X W, et al. Incipient melting behavior and its influences on the mechanical properties of a directionally solidified Ni-based superalloy with high boron content[J]. Acta Metall. Sin., 2017, 53:684(张洪伟,秦学智,李小武等.一种高硼定向凝固合金的初熔行为及其对力学性能的影响[J].金属学报, 2017, 53:684)
[19] Du B N, Shi Z W, Yang J X, et al. M5B3boride at the grain boundary of a nickel-based superalloy[J]. J. Mater. Sci. Technol., 2016,32:265
[20] Wu B P, Li L H, Wu J T, et al. Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys[J]. Int. J. Miner. Metall. Mater., 2014, 21:1120
[21] Hu Z Q, Sun W R, Song H W. A new method for strengthening wrought superalloys-micro-alloying with phosphorus and boron[J]. Eng. Sci., 2005, 3(4):1
[22] Zhu Y X, Zhang S N, Zhang T X, et al. A new way to improve the superalloys[A]. Superalloys 1992[C]. Warrendale, PA:TMS,1992:145)
[23] High Temperature Material Branch of the Chinese Society for Metals. China Superalloys Handbook(Volume Two)[M]. Beijing:Standards Press of China, 2012:93(中国金属学会高温材料分会.中国高温合金手册,下卷[M].北京:中国标准出版社, 2012:93)