梯度多孔Ti-6Al-4V材料疲劳性能研究

Graded porous titanium alloys refer to porous materials with graded porosity along a certain direction. They possess Young's modulus completely compatible with human bones and by adjusting the graded porosity, their strength can be improved and the stress concentration can be reduced simultaneously, which have great potetial application in medical implant field. In this proposal, the open cellure Ti-6Al-4V meshes will be fabricated by Additive manufacturing via Electron Beam Melting (AM-EBM). Through the combinination of experimental investigations and finite element calculations, the effect of different graded porosity on the cyclic ratcheting behaviour of Ti-6Al-4V meshes will be studied. The dislocation structures, slip characteristics, hardening or softening in the cell walls of Ti-6Al-4V meshes with graded porosity during the cyclic deformation will be investigated to elucidate their relationship with the cyclic ratcheting behaviour. With these studies, we try to understand the fatigue mechanism of Ti-6Al-4V meshes with graded porosity. The fulfillment of the project will not only establish a theoretical base for evaluating and forcasting the fatigue life of porous Ti-6Al-4V with graded porosity, but also guide their optimum design and actual medical applications.

梯度多孔钛合金材料是指其孔结构在某个取向上呈梯度变化的多孔材料。它不仅具有完全与人体骨骼匹配的弹性模量，还可以通过孔隙的梯度分布调节，达到提高多孔材料整体强度、减轻应力集中避免功能突变的目的，在医疗领域具有很大发展潜力。本项目拟利用电子束熔化逐层成形法（AM-EBM）制备梯度孔隙分布Ti-6Al-4V开孔多孔材料，结合实验研究和有限元模拟，研究应力控制下不同梯度孔隙分布对多孔Ti-6Al-4V材料循环蠕变行为（循环加速或减速）的影响，考察梯度多孔Ti-6Al-4V材料孔壁在循环应力作用下的位错组态、滑移特征等组织变化、硬化软化规律，阐明孔壁材料的循环形变特性与梯度多孔材料循环蠕变之间的关系，揭示梯度孔隙分布Ti-6Al-4V多孔材料循环形变及疲劳失效机制。该项目的完成不仅可为预测和评价梯度孔隙多孔材料的疲劳性能奠定理论基础，还可为梯度多孔Ti-6Al-4V材料的优化设计和实际应用提供指导。

钛及钛合金多孔材料由于具有与人体骨组织完全匹配的弹性模量、优异的生物相容性，在医用金属植入物领域具有很好的应用前景。本课题以Ti-6Al-4V合金粉末为原料，采用电子束熔融金属快速成型技术，制备出孔隙率大于60%的Ti-6Al-4V多孔材料。对其弹性模量和单向压缩性能研究结果表明，该钛合金多孔材料的动态杨氏模量为0.2~6.3GPa，压缩强度范围为4~113MPa，与人体骨组织基本匹配，适用于制备人体植入物；不同孔形单元多孔材料的单向压缩强度和变形行为主要由施加于孔棱力的屈曲和弯曲分量耦合作用决定；梯度多孔材料的变形行为符合各均匀组份应力-应变响应的权重平均值。对其压缩疲劳性能研究的结果表明，多孔材料疲劳过程的损伤机制为孔壁材料的循环蠕变特性及其疲劳裂纹的萌生与扩展的共同作用，其中前者是决定多孔材料疲劳寿命的主要因素。提高施加于单元孔棱力的屈曲分量，可以显著降低多孔材料的循环蠕变率，阻滞裂纹在孔壁内的扩展，提高材料高州疲劳强度。对于梯度多孔材料，在循环形变过程中在各组成单元内不断发生应力再分配，从而显著抑制疲劳裂纹在多孔材料内的扩展，其疲劳强度主要由各组成单元的循环蠕变特性决定。通过合理调整多孔材料各组成单元的孔形及梯度孔隙分布，可以使多孔材料在低密度下兼具高疲劳强度和高吸收能，其性能远高于均匀孔隙金属多孔材料。