晶体取向和He浓度对bcc-Fe裂纹扩展行为的影响
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摘要
采用分子动力学模拟研究了300 K时不同He浓度下(001)[010]和(121)[111]2种取向bcc-Fe裂纹模型的扩展行为。结果表明,当模型中不存在He时,裂纹取向不同,裂纹扩展机制不同:(001)[010]取向裂纹的扩展机制分为弹性变形、相变、裂纹尖端沿相变区解理断裂;(121)[111]取向裂纹的扩展机制分为弹性变形、堆垛孪晶、孪晶尖端应力集中诱发多空洞合并断裂。(121)[111]取向裂纹的屈服应力和应变大于(001)[010]取向裂纹,说明(121)[111]取向裂纹具有较强的抵制裂纹扩展的能力。He浓度对裂纹扩展行为的影响主要体现在2个方面:当He浓度较低(0.9%,原子分数)时,He的存在减缓了相变或者孪晶转变速率,降低了裂纹扩展速率;当He浓度较高(6.0%,原子分数)时,大量He团簇的存在促进了空洞形成,导致2种裂纹模型的断裂机制均变为He团簇诱发多空洞合并断裂,未出现相变或者孪晶。
Radiation-induced damage, especially the effect of He, has always been one of the crucial issues in future fusion reactors. It is thus essential to further understand the formation of He bubbles and hardening characteristics for future development of fusion application materials, for instance bcc-Fe as a simple model. Behaviors of crack propagation have been investigated in two different orientated cracks(001)[010] and(121)[111] of bcc-Fe models under different densities of He at 300 K by molecular dynamics simulation. The results show that these behaviors are tailored by crack orientations on the condition of non-He atoms:(001)[010] orientated crack can be divided into elastic deformation, phase transformation and cleavage fracture of crack tip along phase transformation zone; however,(121)[111] orientated crack is elastic deformation, stacking twin and after that formation and coalescence of voids to rupture. Furthermore, the yield stress and strain of(121) [111] orientated crack are higher than(001) [010] orientated crack, therefore(121)[111] orientated crack has stronger ability to resist crack propagation. In addition, it is revealed that the influence of He density on the crack propagation exhibits two major aspects: when the density of He is lower(0.9%, atomic fraction), He can reduce the efficiency of phase or twin transformation and decrease the rate of crack propagation; when the density of He is higher(6.0%, atomic fraction), a large number of He clusters contribute to promote micro-voids nucleation, fracture mechanism for both crack models is the transformation of He clusters to voids, then voids coalescence, accelerating the occurrence of fracture. There is no twin or phase transformation in higher density of He.
Radiation-induced damage, especially the effect of He, has always been one of the crucial issues in future fusion reactors. It is thus essential to further understand the formation of He bubbles and hardening characteristics for future development of fusion application materials, for instance bcc-Fe as a simple model. Behaviors of crack propagation have been investigated in two different orientated cracks(001)[010] and(121)[111] of bcc-Fe models under different densities of He at 300 K by molecular dynamics simulation. The results show that these behaviors are tailored by crack orientations on the condition of non-He atoms:(001)[010] orientated crack can be divided into elastic deformation, phase transformation and cleavage fracture of crack tip along phase transformation zone; however,(121)[111] orientated crack is elastic deformation, stacking twin and after that formation and coalescence of voids to rupture. Furthermore, the yield stress and strain of(121) [111] orientated crack are higher than(001) [010] orientated crack, therefore(121)[111] orientated crack has stronger ability to resist crack propagation. In addition, it is revealed that the influence of He density on the crack propagation exhibits two major aspects: when the density of He is lower(0.9%, atomic fraction), He can reduce the efficiency of phase or twin transformation and decrease the rate of crack propagation; when the density of He is higher(6.0%, atomic fraction), a large number of He clusters contribute to promote micro-voids nucleation, fracture mechanism for both crack models is the transformation of He clusters to voids, then voids coalescence, accelerating the occurrence of fracture. There is no twin or phase transformation in higher density of He.
引文
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[31]Fujiwara H,Inomoto H,Sanada R,et al.Nano-ferrite formation and strain-induced-ferrite transformation in an SUS316L austenitic stainless steel[J].Scr.Mater.,2001,44:2039
[32]Ohr S M.An electron microscope study of crack tip deformation and its impact on the dislocation theory of fracture[J].Mater.Sci.Eng.,1985,72:1
[33]Yu X G,Gou F J,Tian X.Molecular dynamics study of the effect of hydrogen on the mechanical properties of tungsten[J].J.Nucl.Mater.,2013,441:324
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[36]Fu R,Rui Z Y,Yan C F,et al.Molecular dynamics simulation of micro-crack propagation behavior in single crystal g-Ti Al[J].J.Funct.Mater.,2015,46:13100(付蓉,芮执元,剡昌锋等.单晶g-Ti Al合金微裂纹扩展行为的分子动力学模拟[J].功能材料,2015,46:13100)
[37]Wu Q,Zikry M A.Prediction of diffusion assisted hydrogen embrittlement failure in high strength martensitic steels[J].J.Mech.Phys.Solids,2015,85:143
[2]Ishiyama Y,Kodama M,Yokota N,et al.Post-irradiation annealing effects on microstructure and helium bubbles in neutron irradiated type 304 stainless steel[J].J.Nucl.Mater.,1996,239:90
[3]Stoller R E,Odette G R.The effects of helium implantation on microstructural evolution in an austenitic alloy[J].J.Nucl.Mater.,1988,154:286
[4]Lewis M B,Farrell K.Migration behavior of helium under displacive irradiation in stainless steel,nickel,iron and zirconium[J].Nucl.Instrum.Methods Phys.Res.,1986,16B:163
[5]Vassen R,Trinkaus H,Jung P.Helium desorption from Fe and V by atomic diffusion and bubble migration[J].Phys.Rev.,1991,44B:4206
[6]Bloom E E.The challenge of developing structural materials for fusion power systems[J].J.Nucl.Mater.,1998,258-263:7
[7]Zinkle S J,Ghoniem N M.Operating temperature windows for fusion reactor structural materials[J].Fusion Eng.Des.,2000,51-52:55
[8]Liu X Y,Xie W B,Chen W X,et al.Effects of grain boundary and boundary inclination on hydrogen diffusion in a-iron[J].J.Mater.Res.,2011,26:2735
[9]Troiano A R.The role of hydrogen and other interstitials in the mechanical behavior of metals[J].Metallogr.Microst.Anal.,2016,5:557
[10]Hirth J P.Effects of hydrogen on the properties of iron and steel[J].Metall.Trans.,1980,11A:861
[11]Li M J,Hu H Y,Xing X S.The relationship between fatigue life and grain size of polycrystalline metals[J].Acta Phys.Sin.,2003,52:2092(李眉娟,胡海云,邢修三.多晶体金属疲劳寿命随晶粒尺寸变化的理论研究[J].物理学报,2003,52:2092)
[12]Zhu L,Zhang A H.Mechanism of crack formation at hard brittle particles in steels[J].Acta Phys.Sin.,2004,53:571(朱亮,张爱华.钢中脆硬粒子裂纹形成机理[J].物理学报,2004,53:571)
[13]Li X F,Fan T Y.Elastic analysis of a mode II crack in a decagonal quasi-crystal[J].Chin.Phys.,2002,11:266
[14]Rice J R.Dislocation nucleation from a crack tip:An analysis based on the Peierls concept[J].J.Mech.Phys.Solids,1992,40:239
[15]Cao L X,Wang C Y.Phonon spectrum and related thermodynamic properties of microcrack in bcc-Fe[J].Chin.Phys.,2006,15:2092
[16]Ma L,Xiao S F,Deng H Q,et al.Molecular dynamics simulation of fatigue crack propagation in bcc iron under cyclic loading[J].Int.J.Fatigue,2014,68:253
[17]UhnákováA,MachováA,Hora P.3D atomistic simulation of fatigue behavior of a ductile crack in bcc iron[J].Int.J.Fatigue,2011,33:1182
[18]UhnákováA,Pokluda J,MachováA,et al.3D atomistic simulation of fatigue behavior of a ductile crack in bcc iron loaded in mode II[J].Comput.Mater.Sci.,2012,61:12
[19]UhnákováA,Pokluda J,MachováA,et al.3D atomistic simulation of fatigue behaviour of cracked single crystal of bcc iron loaded in mode III[J].Int.J.Fatigue,2011,33:1564
[20]Ren G W,Tang T G.Coupling of two-dimensional atomistic and continuum models for dynamic crack[J].Chin.Phys.,2014,23B:118704
[21]Zhou S J,Beazley D M,Lomdahl P S,et al.Large-scale molecular dynamics simulations of three-dimensional ductile failure[J].Phys.Rev.Lett.,1997,78:479
[22]Cao L X,Wang C Y.Molecular dynamics simulation of fracture in a-iron[J].Acta Phys.Sin.,2007,56:413(曹莉霞,王崇愚.a-Fe裂纹的分子动力学研究[J].物理学报,2007,56:413)
[23]Wu W P,Yao Z Z.Molecular dynamics simulation of stress distribution and microstructure evolution ahead of a growing crack in single crystal nickel[J].Theoret.Appl.Fract.Mech.,2012,62:67
[24]Telitchev I Y,Vinogradov O.Numerical tensile tests of BCC iron crystal with various amounts of hydrogen near the crack tip[J].Comput.Mater.Sci.,2006,36:272
[25]Kanezaki T,Narazaki C,Mine Y,et al.Effects of hydrogen on fatigue crack growth behavior of austenitic stainless steels[J].Int.J.Hydrogen Energy,2008,33:2604
[26]Song J,Curtin W A.Atomic mechanism and prediction of hydrogen embrittlement in iron[J].Nat.Mater.,2013,12:145
[27]Song H Y,Zhang L,Xiao M X.Molecular dynamics simulation of effect of hydrogen atoms on crack propagation behavior of a-Fe[J].Phys.Lett.,2016,380A:4049
[28]Martínez E,Schwen D,Caro A.Helium segregation to screw and edge dislocations in a-iron and their yield strength[J].Acta Mater.,2015,84:208
[29]Stukowski A.Visualization and analysis of atomistic simulation data with OVITO—the Open Visualization Tool[J].Modell.Simul.Mater.Sci.Eng.,2009,18:015012
[30]Guo L Y,Chen Z,Long J,et al.Study on the effect of stress state and crystal orientation on micro-crack tip propagation behavior in phase field crystal method[J].Acta Phys.Sin.,2015,64:178102(郭刘洋,陈铮,龙建等.晶体相场法研究应力状态及晶体取向对微裂纹尖端扩展行为的影响[J].物理学报,2015,64:178102)
[31]Fujiwara H,Inomoto H,Sanada R,et al.Nano-ferrite formation and strain-induced-ferrite transformation in an SUS316L austenitic stainless steel[J].Scr.Mater.,2001,44:2039
[32]Ohr S M.An electron microscope study of crack tip deformation and its impact on the dislocation theory of fracture[J].Mater.Sci.Eng.,1985,72:1
[33]Yu X G,Gou F J,Tian X.Molecular dynamics study of the effect of hydrogen on the mechanical properties of tungsten[J].J.Nucl.Mater.,2013,441:324
[34]Hull D.Twinning and fracture of single crystals of 3%silicon iron[J].Acta Metall.,1960,8:11
[35]Bo?anskyJ,?mida T.Deformation twins-probable inherent nuclei of cleavage fracture in ferritic steels[J].Mater.Sci.Eng.,2002,A323:198
[36]Fu R,Rui Z Y,Yan C F,et al.Molecular dynamics simulation of micro-crack propagation behavior in single crystal g-Ti Al[J].J.Funct.Mater.,2015,46:13100(付蓉,芮执元,剡昌锋等.单晶g-Ti Al合金微裂纹扩展行为的分子动力学模拟[J].功能材料,2015,46:13100)
[37]Wu Q,Zikry M A.Prediction of diffusion assisted hydrogen embrittlement failure in high strength martensitic steels[J].J.Mech.Phys.Solids,2015,85:143