纯W高压扭转显微组织演化过程TEM分析
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摘要
在相对较低温度下完成了纯W不同扭转圈数高压扭转实验,通过EBSD、TEM及HRTEM观察了纯W高压扭转过程中的显微组织形貌及微观结构。结果表明,随着等效应变增大,纯W材料显著细化,位错密度增加,非平衡晶界增多。高压扭转过程中小角度晶界向大角度晶界转化现象明显,且位错结构逐渐转移至晶界,细小晶粒内部无明显缺陷。当等效应变增大至5.5时,由于部分晶粒尺寸与位错平均自由程相近,晶粒变形方式由晶内滑移向晶界滑移转变。
Refractory metal tungsten has wide applications in many fields such as aerospace, national defense, military and nuclear industry due to its excellent comprehensive mechanical properties. As the demand for high-performance materials in the new era is increasing, existing materials cannot meet the performance requirements under extreme conditions. The high pressure torsion(HPT) process can produce severe shear deformation and densify the material effectively, leading to ultrafine-grain structure with non-equilibrium grain boundaries and having a significant effect on improving the overall performance of pure tungsten materials. HPT process is used to prepare an ultrafine-grain material with excellent comprehensive performance, which can broaden the application field of refractory metal tungsten and promote the engineering application of high-performance materials. The HPT experiment was carried out on commercial pure tungsten at a relatively low temperature, and the microstructure evolution during HPT processing at various turning numbers has been investigated by means of EBSD, TEM and HRTEM.It was found that with the strain increasing, the grains were refined significantly, dislocation density and the ratio of non-equilibrium grain boundary increased obviously. Moreover, it was transparent that the low angle grain boundary transform into high angle grain boundary during HPT processing. At the same time,the dislocation structure moved to grain boundary gradually so that there was no obvious defect in fined grains. When the equivalent strain increased to 5.5, the deformation mode of grains transformed from intracrystalline sliding to grain boundary sliding, because the size of some grains was close to the mean free path of dislocation.
Refractory metal tungsten has wide applications in many fields such as aerospace, national defense, military and nuclear industry due to its excellent comprehensive mechanical properties. As the demand for high-performance materials in the new era is increasing, existing materials cannot meet the performance requirements under extreme conditions. The high pressure torsion(HPT) process can produce severe shear deformation and densify the material effectively, leading to ultrafine-grain structure with non-equilibrium grain boundaries and having a significant effect on improving the overall performance of pure tungsten materials. HPT process is used to prepare an ultrafine-grain material with excellent comprehensive performance, which can broaden the application field of refractory metal tungsten and promote the engineering application of high-performance materials. The HPT experiment was carried out on commercial pure tungsten at a relatively low temperature, and the microstructure evolution during HPT processing at various turning numbers has been investigated by means of EBSD, TEM and HRTEM.It was found that with the strain increasing, the grains were refined significantly, dislocation density and the ratio of non-equilibrium grain boundary increased obviously. Moreover, it was transparent that the low angle grain boundary transform into high angle grain boundary during HPT processing. At the same time,the dislocation structure moved to grain boundary gradually so that there was no obvious defect in fined grains. When the equivalent strain increased to 5.5, the deformation mode of grains transformed from intracrystalline sliding to grain boundary sliding, because the size of some grains was close to the mean free path of dislocation.
引文
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[28]Staker M R,Holt D L.The dislocation cell size and dislocation density in copper deformed at temperatures between 25 and700℃[J].Acta Metall.,1972,20:569
[2]Lv C C,Liu J X,Li S K,et al.Penetration performance of W-NiFe alloy shaped charge liner[J].Rare Met.Mater.Eng.,2013,42:2337(吕翠翠,刘金旭,李树奎等.W-Ni-Fe合金药型罩的破甲特性[J].稀有金属材料与工程,2013,42:2337)
[3]Roth J,Tsitrone E,Loarte A,et al.Recent analysis of key plasma wall interactions issues for ITER[J].J.Nucl.Mater.,2009,390-391:1
[4]Zhang P,Zhu Q,Qin H Y,et al.Research progress of high temperature materials for aero-engines[J].Mater.Rev.,2014,28(6):27(张鹏,朱强,秦鹤勇等.航空发动机用耐高温材料的研究进展[J].材料导报,2014,28(6):27)
[5]Zhu L X,Yan Q Z,Lang S T,et al.Research progress of tungstenbase materials as plasma facing materials[J].Chin.J.Nonferrous Met.,2012,22:3522(朱玲旭,燕青芝,郎少庭等.钨基面向等离子体材料的研究进展[J].中国有色金属学报,2012,22:3522)
[6]Wu Y C.The routes and mechanism of plasma facing tungsten materials to improve ductility[J].Acta Metall.Sin.,2019,55:171(吴玉程.面向等离子体W材料改善韧性的方法与机制[J].金属学报,2019,55:171)
[7]Li P,Hua R,Xue K M,et al.Research progress in tungsten and its alloys by plastic processing[J].Rare Met.Mater.Eng.,2016,45:529(李萍,华睿,薛克敏等.钨及其合金塑性加工的研究进展[J].稀有金属材料与工程,2016,45:529)
[8]Sabbaghianrad S,Langdon T G.A critical evaluation of the processing of an aluminum 7075 alloy using a combination of ECAPand HPT[J].Mater.Sci.Eng.,2014,A596:52
[9]Wei Q,Zhang H T,Schuster B E,et al.Microstructure and mechanical properties of super-strong nanocrystalline tungsten processed by high-pressure torsion[J].Acta Mater.,2006,54:4079
[10]Faleschini M,Kreuzer H,Kiener D,et al.Fracture toughness investigations of tungsten alloys and SPD tungsten alloys[J].J.Nucl.Mater.,2007,367-370:800
[11]Hao T,Fan Z Q,Zhang T,et al.Strength and ductility improvement of ultrafine-grained tungsten produced by equal-channel angular pressing[J].J.Nucl.Mater.,2014,455:595
[12]Cui Z Z,Lin Y S,Shi G,et al.Effect of annealing temperature on microstructure and internal stress of high purity tungsten target[J].Aerosp.Mater.Technol.,2017,47(4):63(崔子振,林岩松,石刚等.退火温度对高纯钨靶显微组织和内应力的影响[J].宇航材料工艺,2017,47(4):63)
[13]Zhilyaev A P,Nurislamova G V,Kim B K,et al.Experimental parameters influencing grain refinement and microstructural evolution during high-pressure torsion[J].Acta Mater.,2003,51:753
[14]Zhilyaev A P,Langdon T G.Using high-pressure torsion for metal processing:Fundamentals and applications[J].Prog.Mater.Sci.,2008,53:893
[15]El-Tahawy M,Huang Y,Choi H,et al.High temperature thermal stability of nanocrystalline 316L stainless steel processed by highpressure torsion[J].Mater.Sci.Eng.,2017,A682:323
[16]Harai Y,Kai M,Kaneko K,et al.Microstructural and mechanical characteristics of AZ61 magnesium alloy processed by highpressure torsion[J].Mater.Trans.,2008,49:76
[17]Xu C,Horita Z,Langdon T G.The evolution of homogeneity in processing by high-pressure torsion[J].Acta Mater.,2007,55:203
[18]Kecskes L J,Cho K C,Dowding R J,et al.Grain size engineering of bcc refractory metals:Top-down and bottom-up-Application to tungsten[J].Mater.Sci.Eng.,2007,A467:33
[19]Ganeev A V,Islamgaliev R K,Valiev R Z.Refinement of tungsten microstructure upon severe plastic deformation[J].Phys.Met.Metall.,2014,115:139
[20]Zhang Y,Ganeev A V,Gao X,et al.Influence of HPT deformation temperature on microstructures and thermal stability of ultrafinegrained tungsten[J].Mater.Sci.Forum.,2008,584-586:1000
[21]Zhang Y,Ganeev A V,Wang J T,et al.Observations on the ductileto-brittle transition in ultrafine-grained tungsten of commercial purity[J].Mater.Sci.Eng.,2009,A503:37
[22]Li P,Wang X,Xue K M,et al.Microstructure and recrystallization behavior of pure W powder processed by high-pressure torsion[J].Int.J.Refract.Met.Hard Mater.,2016,54:439
[23]Edalati K,Horita Z.A review on high-pressure torsion(HPT)from1935 to 1988[J].Mater.Sci.Eng.,2016,A652:325
[24]Li P,Lin Q,Wang X,et al.Recrystallization behavior of pure molybdenum powder processed by high-pressure torsion[J].Int.J.Refract.Met.Hard Mater.,2018,72:367
[25]Zhao Y H,Bingert J F,Zhu Y T,et al.Tougher ultrafine grain Cu via high-angle grain boundaries and low dislocation density[J].Appl.Phys.Lett.,2008,92:081903
[26]Degtyarev M V,Chashchukhina T I,Voronova L M,et al.Influence of the relaxation processes on the structure formation in pure metals and alloys under high-pressure torsion[J].Acta Mater.,2007,55:6039
[27]Jiang T H,Liu M P,Xie X F,et al.Grain boundary structure of AlMg alloys processed by high pressure torsion[J].Chin.J.Mater.Res.,2014,28:371(蒋婷慧,刘满平,谢学锋等.高压扭转大塑性变形Al-Mg合金中的晶界结构[J].材料研究学报,2014,28:371)
[28]Staker M R,Holt D L.The dislocation cell size and dislocation density in copper deformed at temperatures between 25 and700℃[J].Acta Metall.,1972,20:569