CuZr非晶合金相变诱发塑性机理研究

Amorphous alloy Composites with tailored nanotwin structures become a new direction for scientific research, which exhibit enhanced tensile ductility together with significant work hardening capability. A new experiment mean of observation in situ by means of high resolution transmission electron microscopy with the fluctuation microscopic technique and digital scattering correlation method is put forward to develop the mechanisms of nanotwins existent in phase transforamation inducing plasticity in amorphous alloy matrix composites,on the basis of clarifying the effect of elastic energy accumulation on the plastic deformation.In this project, a Cu-Zr binary alloy system will be selected for investigation. Through the addition of doping elements of Al,Co and Nb, and the control of melting electric current parameters, amorphous alloy composites with size greater than 20 nm and equal distribution of nanocrystalline will be achieved under different cooling rates. Their microstructures will be characterized by advanced analytical techniques, and the nucleation and growth of the nanotwins will be investigated. The plasticity deformation behaviour of amorphous alloy matrix composites with different size, spacing and amount nanotwins will be examined in situ by means of high resolution transmission electron microscopy with the fluctuation microscopic technique under quasi-static tension loading mode. The quantitative relation of the feature of nanotwins and plasticity deformation will be clarified. The elastic deformation behavior and the stress transport between the nanotwin and the amorphous phase in composites will be studied by using digital scattering correlation method. The shear strain transfer mechanism between the nanotwin and the amorphous matrix will be studied. To obtain the mechanisms of phase transformation inducing plasticity of amorphous alloy composites, does not only lead to latent engineering practical applications of Bulk Metallic Glasses, it also has significant academic values and contribution.

具有显著拉伸塑性及加工硬化性能的含纳米孪晶非晶复合材料是一新科学研究方向。项目提出使用具有波动电子显微技术的高分辨透射电镜及数字散斑相关法原位观测新手段，在研究弹性能累积对塑性变形影响的基础上，探究非晶相变产生纳米孪晶诱发塑性机理。选择Cu-Zr二元合金，通过添加Al、Co和Nb元素及控制熔炼电流参数，在不同冷速下制备具有尺寸大于20nm及均匀分布纳米晶的非晶复合材料，使用先进分析技术表征其微观结构，探讨纳米孪晶形核、生长规律。设计具有波动电子显微技术的高分辨透射电镜原位观测准静态单轴拉伸实验，研究不同纳米孪晶尺寸、间距及数量的非晶复合材料塑性变形，建立纳米孪晶特征与塑性变形定量关系。使用数字散斑相关法原位观测非晶复合材料弹性变形及纳米孪晶与非晶相间应力传输。研究纳米孪晶与非晶相间剪切应变转换机制。获得相变诱发非晶复合材料塑性机理具有重要学术研究价值及潜在工程应用前景。

针对非晶合金出现室温脆性和变形软化问题，提出具有显著塑性及加工硬化性能的含纳米晶非晶复合材料。以CuZr基非晶合金及其复合材料为研究对象，利用具有波动电子显微技术的高分辨透射电镜、扫描电镜及数字散斑相关法原位观测手段，同时使用光学显微分析、扫描电镜分析、X射线分析、纳米压痕等手段，应用理论分析与实验测试相结合的方法研究非晶相变产生纳米孪晶诱发塑性机理。在采用铜模铸造技术制备含有纳米晶的CuZr基非晶复合材料基础上，研究添加元素含量及种类、冷却速率及熔炼电流参数对纳米晶尺寸、间距、分布状况及体积分数的影响规律。获得化学成分与非晶复合材料显微组织结构的定量关系。纳米晶分布均匀的最佳非晶复合材料化学成分为Cu44.3Zr48Al4 Nb3.7，拉伸塑性达到7%。设计高分辨透射电镜、扫描电镜原位观测非晶复合材料准静态单轴拉伸实验，揭示了剪切带与原位结构异质性的相互作用，阐明纳米晶诱发塑性的变形机制，研究非晶复合材料弹塑性变形规律：确定非晶复合材料三个变形阶段，即弹性-弹性阶段，弹性-塑性阶段和塑性-塑性阶段。在弹性-弹性和弹性-塑性阶段，屈服强度和弹性极限主要受B2晶体体积分数的影响。在塑性-塑性阶段，B2相激发多剪切带形成，并通过扰动裂纹尖端前方的应力场来偏转剪切带的方向；不稳定B2相形变诱导马氏体相变有助于复合材料塑性变形和加工硬化。采用数字散斑相关法原位观测拉伸过程表面弹塑性应变场变化规律，确定不同纳米晶尺寸及间距复合材料在屈服点弹性剪切应变临界值的变化规律：在弹性变形阶段，横向（纵向）应变场中压缩应变（拉伸应变）随着应力增加逐渐增大；剪切应变场中拉伸应变逐渐增大，同时伴随微弱压缩应变产生，且逐渐出现应变集中条带区越来越明显。在塑性变形阶段，Cu44.3Zr48Al4 Nb3.7复合材料局部剪切应变场中出现明显的拉伸应变和压缩应变集中区域，压缩应变集中区域随应力增加相对增大。本项目研究在非晶合金领域具有较重要的科学意义，并为非晶合金工程应用奠定理论基础。