Al_xCoCrFeNi体系高熵合金室温纳米压入力学行为研究

发布时间：2018-06-29 02:24

本文选题：高熵合金 + 纳米压痕　；参考：《太原理工大学》2017年硕士论文

【摘要】：高熵合金是由多种具有晶格结构的元素(其中每种主要元素都具有较高的原子百分比,约为35%~50%)组合而成的新型合金材料。因具有较高的熵值和固溶强化效应,其力学性能优于传统合金。高熵合金广泛应用在许多领域,例如常被用作高温环境下的涂层材料。因此,研究高熵合金的塑性变形机理具有重要的工程应用背景和科学意义。采用纳米压痕实验研究AlCoCrFeNi高熵合金室温下的力学行为。该纳米压痕实验采用连续刚度法研究了4种不同的压入应变率Al CoCrFeNi高熵合金的纳米压痕变形行为。结果表明,Al CoCrFeNi高熵合金的蠕变变形行为依赖于应变率。压痕原位扫描图显示,在压头周围的实验表明沿压头表面向上隆起,其位置高于初始试件表面,呈现压入凸起现象,表明压头压入的位置产生了严重的局部塑性变形。在不同压入应变率下,其弹性模量基本上保持不变,硬度值由于压痕尺寸效应随着压入深度的增大而下降。研究了AlxCoCrFeNi高熵合金中3种不同铝元素含量对其力学行为的影响。结果表明,当x=1的AlCoCrFeNi高熵合金的弹性模量和硬度均大于铝元素含量为x=0.3,0.5的AlxCoCrFeNi高熵合金的弹性模量和硬度。采用X射线衍射图谱对Al_(0.75)CoCrFeNi高熵合金的微观组织进行表征。Al_(0.75)CoCrFeNi高熵合金的微观结构由面心立方(FCC)固溶体,和体心立方结构(BCC)固溶体两相组成。采用纳米压痕实验对Al_(0.75)CoCrFeNi高熵合金两相的微/纳米力学行为进行研究,结果表明FCC相和BCC相的接触模量和硬度随着最大压入载荷增大而随着压入载荷的增大而增大,在Pmax=10mN时达到最大值,之后趋于稳定。FCC相的弹性模量大于BCC相的弹性模量,而BCC相的硬度值则大于FCC相的硬度值。FCC相和BCC相的消散塑性能随着最大压入载荷的增大而增大。消散塑性能与压入载荷P之间呈现出幂律变化关系。在相同的压入载荷作用下,FCC相晶胞区域的消散塑性能比BCC相晶胞区域的消散塑性能高。采用数值模拟和反分析法相结合研究AlCoCrFeNi高熵合金的微/纳米力学行为。利用ABAQUS有限元软件对AlCoCrFeNi高熵合金准静态纳米压痕实验进行数值模拟,并与其纳米压痕实验数据对比分析,得到实验材料的弹塑性本构关系。将有限元模拟得到的幂律本构方程导入进行有限元模型进行分析,结果表明,给出的本构方程可以较准确地描述AlCoCrFeNi高熵合金的微/纳米力学行为。
[Abstract]:High entropy alloy is a new alloy material composed of a variety of elements with lattice structure (each of which has a high atomic percentage, about 35%). The mechanical properties of the alloy are superior to those of the traditional alloy because of its high entropy value and solid solution strengthening effect. High-entropy alloys are widely used in many fields, such as coating materials under high temperature. Therefore, studying the plastic deformation mechanism of high entropy alloys has important engineering application background and scientific significance. The mechanical behavior of AlCoCrFeNi high entropy alloy at room temperature was studied by nano-indentation test. The nanocrystalline indentation deformation behavior of four Al CoCrFeNi high entropy alloys with different indentation strain rates was studied by continuous stiffness method. The results show that the creep deformation behavior of Al CoCrFeNi high entropy alloy depends on strain rate. The in-situ indentation scanning images show that the indentation surface is raised upward along the head surface, and its position is higher than that of the initial specimen surface, which indicates that the indentation position has serious local plastic deformation. At different indentation strain rates, the elastic modulus remains basically unchanged, and the hardness decreases with the indentation size effect increasing with the indentation depth. The effects of three different aluminum contents on the mechanical behavior of AlxCoCrFeNi high entropy alloy were studied. The results show that the modulus of elasticity and hardness of AlCoCrFeNi high entropy alloy x1 are higher than those of AlxCoCrFeNi high entropy alloy with Al content of xCoCrFeNi 0.5. The microstructure of Al _ (0.75) CoCrFeNi high entropy alloy was characterized by X-ray diffraction. The microstructure of Al _ (0.75) CoCrFeNi high entropy alloy consists of FCC solid solution and bulk centered cubic structure (BCC) solid solution. The micromechanical behavior of Al _ (0.75) CoCrFeNi high entropy alloy was investigated by nano-indentation test. The results show that the contact modulus and hardness of FCC phase and BCC phase increase with the increase of maximum indentation load and increase with the increase of indentation load. The elastic modulus of FCC phase is larger than that of BCC phase, and the hardness value of BCC phase is larger than that of FCC phase. There is a power law relation between the dissipating plastic properties and the indentation load P. Under the same pressure loading, the dissipative plastic properties of FCC phase cell region are higher than that of BCC phase cell area. The micro / nano mechanical behavior of AlCoCrFeNi high entropy alloy was studied by numerical simulation and inverse analysis. The quasi-static nano-indentation test of AlCoCrFeNi high entropy alloy was simulated by Abaqus finite element software, and compared with the experimental data of nano-indentation, the elastic-plastic constitutive relation of the experimental material was obtained. The power law constitutive equation obtained by finite element simulation is introduced into the finite element model for analysis. The results show that the proposed constitutive equation can accurately describe the micro / nano mechanical behavior of AlCoCrFeNi high entropy alloy.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139

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