理想金属晶体纳米压痕过程中晶体失稳的多尺度研究
发布时间：2018-08-22 16:27
【摘要】：晶体失稳作为材料学研究的基础性课题之一,在模拟和实验上已经进行了广泛的研究。但由于受到时间和空间尺度的限制,材料模拟和实验之间的差距较大。材料多尺度模拟的快速发展,为缩小模拟与实验之间的差距创造了条件。建立在Cauchy-Born法则、超弹性本构理论和原子势基础上的相互原子势有限元模型(IPFEM),实现了原子模拟与有限元模拟间的无缝连接。本文对IPFEM模型进行改进,将其应用范围从简单晶体扩展到复式晶体。此外,将软声子分析引入到有限元模拟中,建立晶格动力学有限元模型(LDFEM),进一步增强预测晶体失稳的准确性。运用IPFEM、LDFEM和分子动力学(MD)法研究HCP Co、L10型γ-TiAl、L12型FeNi_3和Ni_3Al等金属晶体的纳米力学行为。采用改进的IPFEM模型研究L12有序结构FeNi_3合金的晶体失稳。在圆柱型纳米压痕中,从IPFEM模拟得到的载荷-位移曲线、压痕应力场和激活的滑移系与MD模拟结果相符。在球型纳米压痕中,晶体失稳位置和压痕应力场与晶体取向有关。采用插值法将晶体失稳时的临界载荷、临界平均接触压强、压痕模量和临界分切应力与晶体取向的关系表示在反极图中。此外,MD模拟结果表明,FeNi_3纳米压痕中位错形核所需的临界载荷以及形核过程与晶体取向有关。纳米压痕中出现的pop-in行为与晶体内位错的形成和反应有关。首个pop-in事件与1/61 1 2型不全位错均匀形核有关。激活的不全位错发生复杂的位错反应形成位错锁。运用IPFEM模型研究了晶体取向对L10有序结构γ-TiAl晶体失稳的影响。研究结果表明,纳米压痕载荷-位移曲线、临界压入深度和临界载荷以及压痕模量与晶面取向有关。详细分析了(0 0 1)、(1 0 0)、(1 0 1)、(1 1 0)和(1 1 1)五个典型晶面纳米压痕过程中的晶体失稳位置和激活的滑移。IPFEM模拟过程中预测到的晶体失稳位置和激活的滑移系与MD模拟过程中观察到的位错形核位置和滑移方式一致。将LDFEM模型用于研究γ-TiAl晶体的晶体失稳。模拟结果表明,γ-TiAl的晶体失稳受加载模式和晶体取向的影响。在单向加载过程中,γ-TiAl晶体失稳表现出明显的拉伸-压缩不对称性。LDFEM模拟得到的应力-应变曲线以及激活的滑移系与MD模拟结果相吻合。在纳米压痕中,接触面法向对应力分布、晶体失稳和位错形核均有显著的影响。LDFEM模型能准确预测晶体的失稳位置和激活的滑移系。LDFEM模型还被用于研究Co晶体在单向拉伸和纳米压痕过程中的声子失稳。模拟结果表明,Co晶体的晶体失稳受加载模式和晶体取向的影响。LDFEM模型能够准确描述Co晶体的拉伸力学行为。在圆柱型纳米压痕过程中,从LDFEM和MD模拟得到的载荷-位移曲线在晶体失稳前保持一致。Co晶体失稳后主要发生基面位错形核。在(0 0 0 1)面球型纳米压痕过程中,出现六个对称的失稳位置。此外,对Ni_3Al晶体的纳米压痕过程进行MD模拟,以研究Ni_3Al晶体的初始塑性。模拟结果表明,Ni_3Al晶体的初始塑性与Shockley不全位错的均匀形核有关。晶体取向、原子势、模型尺寸和温度对晶体发生初始塑性时的临界载荷、临界接触压强、位错形核位置和激活的滑移系均有显著影响。随着压头半径的增加,压痕模量和位错形核深度增加,但最大切应力随压头半径的增加而减小。最大切应力和压痕模量随温度的升高线性下降,位错形核本质上属于应力辅助热激活过程。
[Abstract]:Crystal instability has been extensively studied in both simulation and experiment as one of the fundamental subjects in materials science. However, due to the limitation of time and space scales, the gap between material simulation and experiment is large. The rapid development of multi-scale simulation of materials has created conditions for narrowing the gap between simulation and experiment. Based on Cauchy-Born rule, superelastic constitutive theory and atomic potential, a finite element model of mutual atomic potential (IPFEM) is proposed to realize the seamless connection between atomic simulation and finite element simulation. In this paper, the lattice dynamics finite element model (LDFEM) is established to further enhance the accuracy of predicting crystal instability. The nanomechanical behaviors of HCP Co, L10 type gamma-TiAl, L12 type FeNi_3 and Ni_3Al are studied by using IPFEM, LDFEM and molecular dynamics (MD) methods. The crystal instability of L12 ordered structure FeNi_3 alloy is studied by using the improved IPFEM model. In cylindrical nanoindentation, the load-displacement curves obtained from IPFEM simulation, the indentation stress field and the activated slip system are in agreement with the MD simulation results. In spherical nanoindentation, the crystal instability position and the indentation stress field are related to the crystal orientation. The relationship between the critical shear stress and the crystal orientation is expressed in the inverse pole diagram. In addition, MD simulation results show that the critical load required for dislocation nucleation in FeNi_3 nanoindentation and the nucleation process are related to the crystal orientation. The effect of crystal orientation on the instability of ordered L10-TiAl crystals was studied by using IPFEM model. The results show that nanoindentation load-displacement curves, critical indentation depth, critical load and indentation modulus are related to the crystal plane selection. The position of crystal instability and the slip of activation during the nanoindentation of five typical crystal planes are analyzed in detail. The predicted position of crystal instability and the slip system of activation during IPFEM simulation are consistent with the dislocation nucleation position and slip mode observed during MD simulation. The simulation results show that the instability of the crystal is affected by the loading mode and crystal orientation. During uniaxial loading, the instability of the crystal exhibits obvious tensile-compressive asymmetry. The stress-strain curves obtained by LDFEM simulation and the activated slip system kiss the MD simulation results. In nanoindentation, the normal orientation of the contact surface has a significant effect on the stress distribution, crystal instability and dislocation nucleation. The LDFEM model can accurately predict the location of instability and the active slip system. The LDFEM model is also used to study the phonon instability of Co crystals during uniaxial tension and nanoindentation. The bulk instability is affected by the loading mode and crystal orientation. The LDFEM model can accurately describe the tensile mechanical behavior of Co crystals. The load-displacement curves obtained from LDFEM and MD simulation are consistent before the crystal instability. The dislocation nucleation mainly occurs after the instability of Co crystals. In addition, the nanoindentation process of Ni_3Al crystals was simulated by MD to study the initial plasticity of Ni_3Al crystals. The results show that the initial plasticity of Ni_3Al crystals is related to the homogeneous nucleation of Shockley incomplete dislocations. With the increase of indentation radius, the indentation modulus and the nucleation depth of dislocation increase, but the maximum shear stress decreases with the increase of indentation radius. The maximum shear stress and indentation modulus decrease linearly with the increase of temperature, and the dislocation nucleation base. Qualitatively, it belongs to the stress assisted thermal activation process.
【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG111.2
，
本文编号：2197671
[Abstract]:Crystal instability has been extensively studied in both simulation and experiment as one of the fundamental subjects in materials science. However, due to the limitation of time and space scales, the gap between material simulation and experiment is large. The rapid development of multi-scale simulation of materials has created conditions for narrowing the gap between simulation and experiment. Based on Cauchy-Born rule, superelastic constitutive theory and atomic potential, a finite element model of mutual atomic potential (IPFEM) is proposed to realize the seamless connection between atomic simulation and finite element simulation. In this paper, the lattice dynamics finite element model (LDFEM) is established to further enhance the accuracy of predicting crystal instability. The nanomechanical behaviors of HCP Co, L10 type gamma-TiAl, L12 type FeNi_3 and Ni_3Al are studied by using IPFEM, LDFEM and molecular dynamics (MD) methods. The crystal instability of L12 ordered structure FeNi_3 alloy is studied by using the improved IPFEM model. In cylindrical nanoindentation, the load-displacement curves obtained from IPFEM simulation, the indentation stress field and the activated slip system are in agreement with the MD simulation results. In spherical nanoindentation, the crystal instability position and the indentation stress field are related to the crystal orientation. The relationship between the critical shear stress and the crystal orientation is expressed in the inverse pole diagram. In addition, MD simulation results show that the critical load required for dislocation nucleation in FeNi_3 nanoindentation and the nucleation process are related to the crystal orientation. The effect of crystal orientation on the instability of ordered L10-TiAl crystals was studied by using IPFEM model. The results show that nanoindentation load-displacement curves, critical indentation depth, critical load and indentation modulus are related to the crystal plane selection. The position of crystal instability and the slip of activation during the nanoindentation of five typical crystal planes are analyzed in detail. The predicted position of crystal instability and the slip system of activation during IPFEM simulation are consistent with the dislocation nucleation position and slip mode observed during MD simulation. The simulation results show that the instability of the crystal is affected by the loading mode and crystal orientation. During uniaxial loading, the instability of the crystal exhibits obvious tensile-compressive asymmetry. The stress-strain curves obtained by LDFEM simulation and the activated slip system kiss the MD simulation results. In nanoindentation, the normal orientation of the contact surface has a significant effect on the stress distribution, crystal instability and dislocation nucleation. The LDFEM model can accurately predict the location of instability and the active slip system. The LDFEM model is also used to study the phonon instability of Co crystals during uniaxial tension and nanoindentation. The bulk instability is affected by the loading mode and crystal orientation. The LDFEM model can accurately describe the tensile mechanical behavior of Co crystals. The load-displacement curves obtained from LDFEM and MD simulation are consistent before the crystal instability. The dislocation nucleation mainly occurs after the instability of Co crystals. In addition, the nanoindentation process of Ni_3Al crystals was simulated by MD to study the initial plasticity of Ni_3Al crystals. The results show that the initial plasticity of Ni_3Al crystals is related to the homogeneous nucleation of Shockley incomplete dislocations. With the increase of indentation radius, the indentation modulus and the nucleation depth of dislocation increase, but the maximum shear stress decreases with the increase of indentation radius. The maximum shear stress and indentation modulus decrease linearly with the increase of temperature, and the dislocation nucleation base. Qualitatively, it belongs to the stress assisted thermal activation process.
【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG111.2
，
本文编号：2197671
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