二维非晶纤维/镁合金复合材料强韧性机理研究

Magnesium alloy composites with tailored amorphous microwire structures become a new direction for scientific research, which exhibits enhanced tensile ductility together with higher strength. A new experiment means of observation in situ by use of scanning electron microscope with a tensile stage and digital scattering correlation method is put forward to develop the mechanisms of amorphous microwires improving strength-toughness properties of magnesium alloy composites. In this project, a CoFeSiB two-dimensional metallic glass microwire structure will be developed by weaving and braze welding methods. A MgZnNdZr alloy composite with uniform two-dimensional amorphous microwire structures will be prepared by semi-solid extruding techniques. Their microstructures and interface adhesion mechanisms will be investigated by advanced analytical techniques. The plastic deformation behaviors and fracture mechanisms of magnesium alloy composites with two-dimensional amorphous microwire structures will be examined in situ by means of scanning electron microscope with a tensile stage under quasi-static tension loading mode. The relationship of the feature of amorphous microwire structures and plasticity deformation and fracture strength will be clarified. The elastic deformation behavior and the stress transport between the amorphous microwire and the magnesium alloy matrix will be studied by using digital scattering correlation method. The strain and stress transfer mechanisms between the amorphous microwire and the magnesium alloy matrix will be studied. This project will provide a better understanding of the mechanisms of amorphous microwires improving strength-toughness properties of magnesium alloy composites. It will be expected that this study will lay the solid foundation for the exploration of magnesium alloy composites with high strength-toughness capacity.

具有显著拉伸塑性及高强度非晶纤维/镁合金复合材料是一新科学研究方向。提出使用数字散斑相关法及扫描电镜原位观测新手段，探究非晶纤维提高镁合金强韧性机理。使用编织及钎焊方法制备CoFeSiB二维非晶纤维结构，使用半固态挤压技术制备含二维非晶纤维结构的MgZnNdZr合金复合材料，应用先进分析技术研究其微观结构及界面结合机制。设计扫描电镜原位观测准静态单轴拉伸实验，研究含二维非晶纤维结构镁合金复合材料塑性变形及断裂机制，建立非晶纤维特征与塑性变形及断裂强度关系。使用数字散斑相关法原位观测复合材料弹性变形及非晶纤维与镁合金间应力传输。研究非晶纤维与基体间应力和应变转换机制。深入认识非晶纤维提高镁合金复合材料强韧性机理，为设计及开发高强韧镁合金复合材料提供理论指导。

镁合金具有高的比强度和良好的铸造性能，如何进一步提高其强韧性是研究的重点。本研究采用高强度非晶纤维增强的方法制备镁合金/非晶纤维复合材料。采用熔体抽拉法制备了具有高晶化温度的非晶纤维，平均强度达到2833.87MPa，适合作为镁合金增强体。利用自行设计的设备，采用挤压铸造法制备了非晶纤维增强镁基复合材料，通过保压时间、熔体温度及非晶丝预热温度等参数研究，优化了制备工艺，获得了界面结合良好的镁合金/非晶纤维复合材料，强韧性明显提高。采用SEM、TEM分析了界面非晶纤维与镁合金基体的界面，采用Miedema混合焓模型分析界面反应规律。Ni元素向镁合金基体中扩散，在Ni基非晶纤维边缘形成4-12μm厚的扩散层，在扩散层内形成少量的Mg-Ni化合物。随着温度的升高，界面反应物增加，界面结合强度增强，而非晶纤维未出现晶化现象。采用数字散斑相关法原位分析了复合材料变行行为，通过局部应变分析，确定了非晶纤维增强复合材料应变规律。剪切应变集中明显增加，弹性区内近似平行Y方向，塑性阶段方向性消失，等应变线形状趋于圆形，并随应力增加，剪切应变的集中现象明显。在拉伸件载荷下，裂纹萌生后可以通过界面传递载荷，载荷继续加大，最弱的Ni基非晶纤维开始断裂，在应力集中下使界面脱粘，裂纹沿纤维表面纵向扩张，而其它完整的非晶纤维继续承受载荷，随后拔出断裂，往复发生，直到完全断开。应力集中因为界面脱粘及镁基体塑性变形而得到松弛，促使裂纹停止扩展，这种裂纹扩展方式充分发挥了非晶纤维的增强作用，使镁合金/非晶纤维复合材料的强度和塑性得到提高。