强基面织构超细晶和细晶纯镁冷拉拔塑性变形机理研究

With excellent biocompatibility, pure magnesium has a bright future in the field of biomedical material. However, hexagonal close-packed (HCP) structured pure Mg has low symmetry of slip systems that contribute to low ductility and the development of strong basal texture. In this project, the accumulative high ratio extrusion process will be adopted to design the microstructure of pure Mg in order to improve its low strength and poor ductility simultaneously. The contributions of non-basal dislocations and grain boundary sliding to the plastic strain at room temperature will be significantly increased through grain refinement. Moreover, the room temperature plasticity of pure magnesium was improved. Then, an idea that a large plastic deformation was gradually realized through multiple accumulation of single small deformation was proposed in this project. Under the guidance of this idea, the pure magnesium thin-walled fine tube will be successfully fabricated by cold drawing process using the ultrafine and fine grained pure Mg with strong basal texture as raw material. The relationships among cold drawing formability of above-mentioned pure magnesium, its original microstructure, mechanical properties and cold drawing process parameters will be elucidated by comprehensive analysis of the effects of drawing methods, deformation degree and cold drawing speed on the microstructure, texture and mechanical properties of the pure magnesium. The cold-drawn plastic deformation mechanisms in the ultrafine and fine grained pure magnesium with strong basal fiber texture would be revealed based on the contributions of dislocation glide, twinning and grain boundary sliding to the strain induced by cold drawing deformation, by which a better understanding on mechanism of pure magnesium cold plastic deformation would be achieved.

纯镁以其优异的生物相容性，在生物医用材料应用领域前景光明。但密排六方晶体结构特征决定了纯镁在室温塑性变形过程中可启动的滑动系少，且易形成强基面织构，降低塑性变形能力。针对纯镁强度低、塑性差等缺点，本项目拟采用累积大比率挤压工艺对纯镁的组织结构进行设计，通过晶粒细化，增加以非基面位错滑移和晶界变形为主的变形模式对塑性应变的贡献，提高纯镁的室温塑性。采用单次小变形、多次累积逐渐实现大塑性变形的思想，以具有强基面织构特征的超细晶和细晶纯镁为原料，冷拉拔成形纯镁薄壁细管。综合分析拉拔方式、变形量、冷拔速度等因素对纯镁组织、织构和力学性能变化的影响，阐明纯镁冷拉拔成形性能与其组织结构、力学性能及冷拉拔工艺之间的关系。以表征位错滑移、孪生和晶界滑移等机制对冷拉拔塑性变形的作用为基础，揭示具有强基面织构特征的超细晶和细晶纯镁冷拉拔塑性变形机理，深化对纯镁冷塑性变形机理的理解。

纯镁以其优异的生物相容性，在可吸收生物医用材料领域具有广阔的应用前景。但密排六方晶体结构特征决定了纯镁在室温塑性变形过程中可启动的滑移系少，且极易形成强基面织构，降低塑性变形能力。针对纯镁强度低、塑性差、加工硬化能力弱等缺点，本项目基于“单次小变形、多次累积逐渐实现纯镁大塑性变形”的思想，采用多道次反向温度场挤压技术，实现了纯镁显微组织的细化，增加非基面滑移、晶界滑移等辅助变形模式，提高了具有强基面织构特征的超细晶和细晶纯镁的冷拉拔变形能力。研究了具有强基面织构特征的超细晶和细晶纯镁在冷拉拔变形过程中组织、织构和力学性能的演化规律，分析了其“冷拉拔工艺-组织、力学性能-冷拉拔成形性能”之间关系，掌握了用于血管支架的纯镁薄壁细管的冷拉拔塑性成形技术。通过研究位错滑移、孪生和晶界滑移等机制对冷拉拔塑性变形的影响，揭示具有强基面织构特征的超细晶和细晶纯镁冷拉拔塑性变形机制，阐明其良好冷拉拔性能产生的原因。本项目的开展，科学上有助于深化纯镁冷塑性变形及其再结晶行为的认识；工程上为可吸收医用纯镁或镁合金血管支架、缝合线的开发与应用提供指导意义。