镁合金中位错的高分辨Z衬度成像研究
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摘要
利用Z衬度成像技术研究了两种耐热镁合金Mg_(97)Zn_1Y_2与Mg_(97)Zn_1Gd_2(at.%)中的位错。塑性变形过程中形成的倾侧晶界上周期性分布的基面〈a〉位错分解形成层错,伴随合金元素在层错上富集可以形成类似长周期堆垛的结构,能够钉扎晶界并抑制晶界高温软化。随着应变量增加,观察到了基面〈a〉位错与锥面〈c+a〉位错构成的复合倾侧晶界,以及单纯由〈c+a_(60)〉位错或〈c+a_s〉位错重排构成的晶界,表明开动了〈c+a〉锥面滑移系,有利于协调材料变形。合金元素在位错处偏聚形成柯垂尔气团,可以强化材料。热变形过程中Gd元素在Mg基体内位错的张应变区富集形成柯垂尔气团,加速β′-Mg_7Gd柱面析出相的异质形核生长。
Dislocations in two heat-resistant Mg alloys, Mg_(97)Zn_1Y_2 and Mg_(97)Zn_1Gd_2(at.%), were studied using aberration-corrected Z-contrast imaging techniques. Dissociation of basal 〈a〉 dislocations and associated segregation of solute atoms produced local structures like long-periodic stacking ordered phases at tilt GBs formed during plastic deformation, which may play an important role in both pinning the GBs and preventing them from softening at elevated temperatures. GBs composed of 〈c+a〉 dislocations were formed due to the activation of pyramidal slip systems with increasing plastic strain. Pyramidal slip of 〈c+a〉 dislocations is important for ductility of Mg alloys. Solute segregation along dislocations in the form of Cottrell atmospheres during hot deformation, not only plays an important role in strengthening by directly impeding dislocation motion, but also facilitates heterogeneous nucleation and growth of strengthening precipitates. These findings about dislocations provide insights on the strengthening and toughening mechanisms in Mg alloys.
Dislocations in two heat-resistant Mg alloys, Mg_(97)Zn_1Y_2 and Mg_(97)Zn_1Gd_2(at.%), were studied using aberration-corrected Z-contrast imaging techniques. Dissociation of basal 〈a〉 dislocations and associated segregation of solute atoms produced local structures like long-periodic stacking ordered phases at tilt GBs formed during plastic deformation, which may play an important role in both pinning the GBs and preventing them from softening at elevated temperatures. GBs composed of 〈c+a〉 dislocations were formed due to the activation of pyramidal slip systems with increasing plastic strain. Pyramidal slip of 〈c+a〉 dislocations is important for ductility of Mg alloys. Solute segregation along dislocations in the form of Cottrell atmospheres during hot deformation, not only plays an important role in strengthening by directly impeding dislocation motion, but also facilitates heterogeneous nucleation and growth of strengthening precipitates. These findings about dislocations provide insights on the strengthening and toughening mechanisms in Mg alloys.
引文
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[16] 汪涛,孙威,王子荣,等. Mg-Y-Nd-Zn合金中LPSO的存在对孪晶形成的影响[J]. 电子显微学报,2016,35(5):393-398.
[17] HU W W, YANG Z Q, LIU J F, et al. Creep of a Mg-Zn-Y alloy at elevated temperatures. In: SINGH A, SOLANKI K, MANUEL MV, et al, eds. Magnesium Technology [C]. Nashville:Wiley,2016:169-174.
[18] HU W W, YANG Z Q, YE H Q. Cottrell atmospheres along dislocations in long-period stacking ordered phases in a Mg-Zn-Y alloy [J]. Scripta Materialia,2016,117:77-80.
[19] YANG Z Q, CHISHOLM M F, DUSCHER G, et al. Direct observation of dislocation dissociation and Suzuki segregation in a Mg-Zn-Y alloy by aberration-corrected scanning transmission electron microscopy [J]. Acta Materialia,2013,61: 350-359.
[20] HU W W, YANG Z Q, YE H Q. 〈c+a〉 dislocations and their interactions with other crystal defects in a Mg alloy [J]. Acta Materialia, 2017, 124:372-382.
[21] HIRTH J P, LOTHE J. Theory of dislocations [M]. 2nd ed. New York: John Wiley & Sons, 1982.
[22] PENNYCOOK S J. Z-contrast STEM for materials science [J]. Ultramicroscopy, 1989, 30:58-69.
[23] HTCH M J,PUTAUX J L,PENISSON J M. Measurement of the displacement field of dislocations to 0.03 angstrom by electron microscopy [J]. Nature, 2003, 423:270-273.
[24] HU W W, YANG Z Q, YE H Q. Sliding and migration of tilt grain boundaries in a Mg-Zn-Y alloy [J]. Advanced Engineeing Materials,2018,20(1):1700516.
[25] ANYANWU I A, KAMADO S, KOJIMA Y. Aging characteristics and high temperature tensile properties of Mg-Gd-Y-Zr alloys [J]. Materials Transactions, 2001,42:1206-1211.
[26] 胡伟伟. 耐热镁合金中位错的原子分辨率电子显微学研究 [D]. 沈阳:中国科学院金属研究所,2018.
[27] NIE J F, WILSON N C, ZHU Y M, et al. Solute clusters and GP zones in binary Mg-RE alloys [J]. Acta Materialia, 2016, 106:260-271.
[28] NATARAJAN A R, Van Der VEN A. A unified description of ordering in HCP Mg-RE alloys [J]. Acta Materialia, 2017, 124:620-632.
[2] POLLOCK T M. Weight loss with magnesium alloys [J]. Science, 2010,328(5981):986-987.
[3] VON MISES R. Mechanics of the ductile form changes of crystals [J]. Z Angew Math Mech,1928,8:161-185.
[4] 泰靖,周博,隋曼龄. AZ31镁合金形变扭折带中【math52z】孪生行为的电子显微学研究 [J]. 电子显微学报, 2017,36(6):547-551.
[5] YOO M H. Slip, twinning, and fracture in hexagonal close packed metals [J]. Metallurgical Transactions A, 1981, 12:409-418.
[6] YOO M H, MORRIS J R, HO K M, et al. Nonbasal deformation modes of HCP metals and alloys: role of dislocation source and mobility [J]. Metallurgical and Materials Transactions A, 2002, 33(3):813-822.
[7] AGNEW S R, HORTON J A, YOO M H. Transmission electron microscopy investigation of 〈c+a〉 dislocations in Mg and alpha-solid solution Mg-Li alloys [J]. Metallurgical and Materials Transactions A,2002,33:851-858.
[8] AGNEW S R, MEHROTRA P, LILLO T M, et al. Texture evolution of five wrought magnesium alloys during route A equal channel angular extrusion: experiments and simulations [J]. Acta Materialia,2005,53(11):3135-3146.
[9] NIE J F, GAO X, ZHU S M. Enhanced age hardening response and creep resistance of Mg-Gd alloys containing Zn [J]. Scripta Materialia,2005,53(9):1049-1053.
[10] NIE J F. Precipitation and hardening in magnesium Alloys [J]. Metallurgical and Materials Transactions A,2012,43(11):3891-3939.
[11] VOSTRY P,SMOLA B,STULIKOVA I,et al. Microstructure evolution in isochronally heat treated Mg-Gd alloys [J]. Phys Status Solidi A, 1999, 175(2):491-500.
[12] HE S M,ZENG X Q,PENG L M,et al. Precipitation in a Mg-10Gd-3Y-0.4Zr (wt.%) alloy during isothermal ageing at 250 ℃ [J]. Journal of Alloys and Compounds,2006,421(1):309-313.
[13] SHAO X H, YANG Z Q, MA X L. Strengthening and toughening mechanisms in Mg-Zn-Y alloy with a long period stacking ordered structure [J]. Acta Materialia,2010,58:4760-4771.
[14] 刘小清,赵东山,叶礼,等. RE(RE=Dy,Er)元素对Mg-Zn系合金微观结构及力学性能的影响 [J]. 电子显微学报,2018,37(2):101-109.
[15] KAWAMURA Y, YAMASAKI M. Formation and mechanical properties of Mg97Zn1RE2 aqlloys with long-period stacking ordered structure [J]. Materials Transactions,2007,48(11):2986-2992.
[16] 汪涛,孙威,王子荣,等. Mg-Y-Nd-Zn合金中LPSO的存在对孪晶形成的影响[J]. 电子显微学报,2016,35(5):393-398.
[17] HU W W, YANG Z Q, LIU J F, et al. Creep of a Mg-Zn-Y alloy at elevated temperatures. In: SINGH A, SOLANKI K, MANUEL MV, et al, eds. Magnesium Technology [C]. Nashville:Wiley,2016:169-174.
[18] HU W W, YANG Z Q, YE H Q. Cottrell atmospheres along dislocations in long-period stacking ordered phases in a Mg-Zn-Y alloy [J]. Scripta Materialia,2016,117:77-80.
[19] YANG Z Q, CHISHOLM M F, DUSCHER G, et al. Direct observation of dislocation dissociation and Suzuki segregation in a Mg-Zn-Y alloy by aberration-corrected scanning transmission electron microscopy [J]. Acta Materialia,2013,61: 350-359.
[20] HU W W, YANG Z Q, YE H Q. 〈c+a〉 dislocations and their interactions with other crystal defects in a Mg alloy [J]. Acta Materialia, 2017, 124:372-382.
[21] HIRTH J P, LOTHE J. Theory of dislocations [M]. 2nd ed. New York: John Wiley & Sons, 1982.
[22] PENNYCOOK S J. Z-contrast STEM for materials science [J]. Ultramicroscopy, 1989, 30:58-69.
[23] HTCH M J,PUTAUX J L,PENISSON J M. Measurement of the displacement field of dislocations to 0.03 angstrom by electron microscopy [J]. Nature, 2003, 423:270-273.
[24] HU W W, YANG Z Q, YE H Q. Sliding and migration of tilt grain boundaries in a Mg-Zn-Y alloy [J]. Advanced Engineeing Materials,2018,20(1):1700516.
[25] ANYANWU I A, KAMADO S, KOJIMA Y. Aging characteristics and high temperature tensile properties of Mg-Gd-Y-Zr alloys [J]. Materials Transactions, 2001,42:1206-1211.
[26] 胡伟伟. 耐热镁合金中位错的原子分辨率电子显微学研究 [D]. 沈阳:中国科学院金属研究所,2018.
[27] NIE J F, WILSON N C, ZHU Y M, et al. Solute clusters and GP zones in binary Mg-RE alloys [J]. Acta Materialia, 2016, 106:260-271.
[28] NATARAJAN A R, Van Der VEN A. A unified description of ordering in HCP Mg-RE alloys [J]. Acta Materialia, 2017, 124:620-632.