超细晶Cu的剧塑性流变行为及本构理论
发布时间：2018-07-13 21:57
【摘要】：在提高金属材料强度方法方面，晶粒细化是在不影响材料韧性的情况下提高金属强度的最有效方法之一。在诸多通过剧烈塑性变形的晶粒细化工艺方法中，等径角通道挤压技术（ECAE, Equal Channel Angle Extrusion）作为一种典型有效的方法，已被广泛应用于各种金属材料的晶粒细化。纯铜作为一种在各个领域被广泛使用的材料，其晶粒细化一直受到研究者的关注。 在本文工作中，为了揭示通过ECAE制备的超细晶Cu的剧塑性流变行为及其本构关系，首先对超细晶Cu在不同应变率下的力学特性进行了研究，然后结合纳米压痕技术对超细晶铜在不同道次下的硬度进行研究分析，研究了不同道次对纯铜热激活体积和应变率敏感性的影响性，对变形机理进行分析，最后为了对这种超细晶Cu的塑性流动本构关系进行研究，首先基于金属塑性流动的热激活位错滑移机理，以典型钢DH36等金属材料塑性流动本构关系研究为基础，再结合超细晶铜Cu的剧塑性流变的特点，获得了DH36钢和超细晶Cu的塑性流动本构关系，本论文研究内容如下： （1）为了测试超细晶Cu在不同应变率下的剧塑性变形力学特性，利用MTS试验机与分离式Hopkinson压杆技术对超细晶Cu材料分别了进行10-3/s和约4,000/s应变率下的力学特性进行了测试，结果表明在10-3/s应变率下，随着挤压道次数的增加，Cu的流动应力呈现先增大而后逐渐减小至稳定状态的趋势，而在约4,000/s应变率的动态加载下，随着挤压道次数的增加，材料的流动行为则表现为逐渐增大进而稳定的趋势。 （2）为了研究超细晶Cu硬度与挤压道次、应变率的关系，基于纳米压痕技术，通过应变率阶跃试验，获得材料在不同应变率下的硬度随着道次增加的变化关系，通过对其应变率敏感性以及热激活体积进行分析发现，随着变形的增加，超细晶Cu的应变率敏感性呈现增加的趋势，而热激活体积则是先减小而后趋于稳定的趋势。 （3）为了揭示超细晶Cu晶界取向对流动应力的影响，文中基于Gourdet的再结晶以及晶界迁移理论的三参数本构模型推导出流动应力与晶界取向演化、亚晶内位错密度以及晶粒尺度的关系式，揭示了随着大角晶界比例的增加，材料的屈服应力下降，进而对应变率敏感性以及热激活体积的变化趋势进行理论解释。 （4）为了研究不同挤压道次下材料的微观结构，基于背散射电子衍射（EBSD, electronbackscattering diffraction）技术，，对4种代表道次的试样进行了微观分析，结果显示，随着挤压道次增加到32道次，大角晶界的比例增加到41%，晶粒尺度下降到341nm；而对于具有相同等效变形的试样，晶粒尺度以及大角晶界的比例会严重影响材料的力学性能。 （5）为了获得超细晶Cu的剧塑性流动本构方程，首先基于物理概念塑性流动本构理论，结合系统试验与唯象本构方法，对典型金属材料DH-36钢等几种材料的塑性流动本构关系进行了系统研究。然而，通过对这类模型进行理论分析发现，这类物理概念模型并不适用于材料剧塑性变形。为此，文中作者借鉴了这些金属的塑性流动本构关系研究思路和方法，基于纳米压痕试验结果，建立了应变率耦合下的剧塑性变形流动本构关系，通过与试验数据对照，模型预测结果与试验结果吻合良好。
[Abstract]:Grain refinement is one of the most effective methods to improve the strength of metal without affecting the toughness of the material. In the process of grain refinement through severe plastic deformation, ECAE, Equal Channel Angle Extrusion, as a typical effective method, has been used as a typical and effective method. Grain refinement is widely used in all kinds of metal materials. Pure copper is widely used as a material in various fields. Its grain refinement has been paid much attention by researchers.
In this work, in order to reveal the plastic rheological behavior and its constitutive relation of ultrafine crystal Cu prepared by ECAE, the mechanical properties of ultrafine crystal Cu under different strain rates were studied first, and then the hardness of ultrafine crystal copper under different channel times was studied by nano indentation technology, and the different channels were studied on pure copper. The effect of thermal activation volume and strain rate sensitivity is analyzed. Finally, in order to study the constitutive relationship of the plastic flow of this superfine crystal Cu, first based on the mechanism of the thermal activated dislocation slip of the metal plastic flow, based on the study of the plastic flow constitutive relation of the typical steel DH36 and other metal materials, then the superfine crystal is combined. The plastic flow constitutive relationship of DH36 steel and ultrafine grained Cu has been obtained by the plastic rheological behavior of Cu Cu.
(1) in order to test the mechanical and plastic deformation mechanical properties of superfine crystal Cu at different strain rates, the mechanical properties of ultra-fine crystal Cu materials under 10-3/s and 4000/s strain rate were tested by MTS test machine and separate Hopkinson pressure rod technique. The results showed that the flow of Cu under the 10-3/s strain rate, with the increase of the number of extrusion channels, the flow of Cu. The dynamic stress tends to increase first and then gradually decrease to the stable state, but under the dynamic loading of the strain rate of 4000/s, with the increase of the number of extrusion channels, the flow behavior of the material increases gradually and then the trend of stability.
(2) in order to study the relationship between the hardness of the superfine crystal and the strain rate of the extrusion channel and the strain rate, based on the nanoindentation technology, the strain rate step test was used to obtain the change of the hardness of the material at different strain rates with the increase of the channel. By analyzing the strain rate sensitivity and the thermal activation volume, the superfine crystal Cu was found to increase with the increase of the strain rate. The strain rate sensitivity showed an increasing trend while the thermal activation volume decreased first and then stabilized.
(3) in order to reveal the influence of the grain boundary orientation on the flow stress of the superfine crystal Cu, based on the recrystallization and the three parameter constitutive model of the grain boundary migration theory, the relationship between the flow stress and grain boundary orientation evolution, the intragranular dislocation density and the grain size are deduced, which reveals that the yield of the material increases with the increase of the grain boundary ratio in the large angle. A theoretical explanation is given for the variation of the force and the change trend of thermal activation volume.
(4) in order to study the microstructure of the material under different extrusion channels, the microanalysis of 4 representative sample samples was carried out based on EBSD (electronbackscattering diffraction) technology. The results showed that as the extrusion channel increased to 32 times, the proportion of the grain boundary in the large angle increased to 41%, and the grain size decreased to 341nm. For specimens with the same equivalent deformation, the ratio of grain size and large angle grain boundary will seriously affect the mechanical properties of the material.
(5) in order to obtain the plastic flow constitutive equation of superfine crystal Cu, based on the physical concept plastic flow constitutive theory and the system test and phenomenological constitutive method, the plastic flow constitutive relation of DH-36 steel, such as the typical metal material, is systematically studied. The physical conceptual model does not apply to the plastic deformation of the material. Therefore, the author draws on the research ideas and methods of the plastic flow constitutive relations of these metals. Based on the results of the nanoindentation test, the constitutive relation of the plastic deformation flow under the strain rate coupling is established. The model prediction results and the experimental results are compared with the experimental data. The fruit is in good agreement.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.11
本文编号：2120864
[Abstract]:Grain refinement is one of the most effective methods to improve the strength of metal without affecting the toughness of the material. In the process of grain refinement through severe plastic deformation, ECAE, Equal Channel Angle Extrusion, as a typical effective method, has been used as a typical and effective method. Grain refinement is widely used in all kinds of metal materials. Pure copper is widely used as a material in various fields. Its grain refinement has been paid much attention by researchers.
In this work, in order to reveal the plastic rheological behavior and its constitutive relation of ultrafine crystal Cu prepared by ECAE, the mechanical properties of ultrafine crystal Cu under different strain rates were studied first, and then the hardness of ultrafine crystal copper under different channel times was studied by nano indentation technology, and the different channels were studied on pure copper. The effect of thermal activation volume and strain rate sensitivity is analyzed. Finally, in order to study the constitutive relationship of the plastic flow of this superfine crystal Cu, first based on the mechanism of the thermal activated dislocation slip of the metal plastic flow, based on the study of the plastic flow constitutive relation of the typical steel DH36 and other metal materials, then the superfine crystal is combined. The plastic flow constitutive relationship of DH36 steel and ultrafine grained Cu has been obtained by the plastic rheological behavior of Cu Cu.
(1) in order to test the mechanical and plastic deformation mechanical properties of superfine crystal Cu at different strain rates, the mechanical properties of ultra-fine crystal Cu materials under 10-3/s and 4000/s strain rate were tested by MTS test machine and separate Hopkinson pressure rod technique. The results showed that the flow of Cu under the 10-3/s strain rate, with the increase of the number of extrusion channels, the flow of Cu. The dynamic stress tends to increase first and then gradually decrease to the stable state, but under the dynamic loading of the strain rate of 4000/s, with the increase of the number of extrusion channels, the flow behavior of the material increases gradually and then the trend of stability.
(2) in order to study the relationship between the hardness of the superfine crystal and the strain rate of the extrusion channel and the strain rate, based on the nanoindentation technology, the strain rate step test was used to obtain the change of the hardness of the material at different strain rates with the increase of the channel. By analyzing the strain rate sensitivity and the thermal activation volume, the superfine crystal Cu was found to increase with the increase of the strain rate. The strain rate sensitivity showed an increasing trend while the thermal activation volume decreased first and then stabilized.
(3) in order to reveal the influence of the grain boundary orientation on the flow stress of the superfine crystal Cu, based on the recrystallization and the three parameter constitutive model of the grain boundary migration theory, the relationship between the flow stress and grain boundary orientation evolution, the intragranular dislocation density and the grain size are deduced, which reveals that the yield of the material increases with the increase of the grain boundary ratio in the large angle. A theoretical explanation is given for the variation of the force and the change trend of thermal activation volume.
(4) in order to study the microstructure of the material under different extrusion channels, the microanalysis of 4 representative sample samples was carried out based on EBSD (electronbackscattering diffraction) technology. The results showed that as the extrusion channel increased to 32 times, the proportion of the grain boundary in the large angle increased to 41%, and the grain size decreased to 341nm. For specimens with the same equivalent deformation, the ratio of grain size and large angle grain boundary will seriously affect the mechanical properties of the material.
(5) in order to obtain the plastic flow constitutive equation of superfine crystal Cu, based on the physical concept plastic flow constitutive theory and the system test and phenomenological constitutive method, the plastic flow constitutive relation of DH-36 steel, such as the typical metal material, is systematically studied. The physical conceptual model does not apply to the plastic deformation of the material. Therefore, the author draws on the research ideas and methods of the plastic flow constitutive relations of these metals. Based on the results of the nanoindentation test, the constitutive relation of the plastic deformation flow under the strain rate coupling is established. The model prediction results and the experimental results are compared with the experimental data. The fruit is in good agreement.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.11
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