Manufacturability of porosity-gradient superelastic load-bearing structures for biomedical applications

材料科学与技术领域的拟议研究活动主要集中在通过选择性激光熔化技术（SLM）实现功能梯度材料和结构（FGM/S）的可制造性。FGM/S对医疗和航空航天应用特别有吸引力。在医学上，从有利于骨长入的多孔结构到多孔性较小的承重结构的受控过渡的单件式植入物应降低与植入物整合问题相关的并发症风险，同时确保足够的机械支撑。在航空航天领域，金属/陶瓷FGM/S将金属的高韧性、强度和可加工性与陶瓷的耐热、耐磨和抗氧化性相结合，可使某些发动机部件达到最佳性能。目前的研究计划主要集中在FGM/S的生物医学应用上，并有可能扩展到航空航天应用。为了生产金属材料，将同时探索两种技术路线：铸锭基和粉末基。基于锭的路线遵循从熔化的锭到通过雾化的粉末的共同路径。反过来，基于粉末的路线意味着使用金属粉末的机械合金化（MA）来生产给定组成和粒度的原料。在该计划的框架内，MA技术在合金元素和粉末尺寸方面的显著灵活性将被利用来生产目标成分的钛合金。对于最终产品制造，将应用SLM技术。鉴于SLM技术在工艺灵活性方面的巨大潜力，主要重点将是通过数值建模和实验进行优化。优化加工、表征和质量控制程序时将考虑以下输出参数：精度、表面光洁度、加工相关各向异性、残余应力、微观和宏观结构以及静态和动态机械性能。鉴于我们在形状记忆钛基合金（Ti-Ni金属间化合物和近β Ti-Nb-X合金）的开发、加工和应用方面的长期经验，以及与其他钛合金相比的显著优势：超弹性、形状恢复和增强的阻尼能力，我们将继续专注于这组金属材料。为了充分利用本研究项目实施过程中获得的知识，将使用所获得的基准SLM工艺参数设计、制造和体外测试真实的承重梯度密度骨替代物，例如颈椎前路植入物。本项目的结果旨在将新型增材制造技术与高性能材料和结构相结合，将促进下一代FGM/S在医学上的成功应用，并有可能在航空航天中应用。最后，拟议的计划将有助于培养高素质的人才，并吸引高水平的外国学生到加拿大。他们将获得材料和新型成型工艺领域的创新技术和尖端专业知识，并将在多学科方法（材料科学，冶金和机械工程）中进行培训。这种丰富的培训将使参与的学生和研究人员具有竞争优势，因为加拿大蓬勃发展的卫生技术和航空航天工业越来越多地寻求接受这种培训的人员。

The proposed research activities in the field of materials science and technology are focused on the manufacturability of functionally-graded materials and structures (FGM/S) by means of the selective laser melting technique (SLM). FGM/S could be especially attractive for medical and aerospace applications. In medicine, single-piece implants with controlled transition from a porous structure favorable for bone ingrowth to a less porous load-bearing structure should reduce the risks of complications related to implant integration problems, while assuring adequate mechanical support. In aerospace, metal/ceramic FGM/S combining the high toughness, strength and machinability of metals with the heat, wear, and oxidation resistance of ceramics should result in the optimum performance of certain engine components. The present research program is mainly focused on the FGM/S’ biomedical applications, with potential extension to aerospace applications.To produce the stock metallic material, two technological routes will be explored concurrently: ingot-based and powder-based. The ingot-based route follows the common path from the melted ingot to powder through atomisation. In turn, the powder-based route implies the use of mechanical alloying (MA) of metal powders to produce the stock material of a given composition and granulometry. In the framework of this program, the significant flexibility of the MA technology in terms of alloying elements and powder size will be exploited to produce titanium alloys of target compositions. For the final product manufacturing, the SLM technique will be applied. Given the significant potential of SLM technology in terms of the process flexibility, the main focus will be on its optimisation through numerical modeling and experimentation. The following output parameters will be taken into consideration for optimizing the processing, characterization and quality control procedures: accuracy, surface finish, processing-dependant anisotropy, residual stresses, micro- and macrostructure, and static and dynamic mechanical properties. Given our long-term experience in the development, processing and application of shape memory titanium-based alloys (Ti-Ni intermetallics and near-beta Ti-Nb-X alloys), and their significant advantages as compared to other titanium alloys: superelasticity, shape restoration and enhanced damping capacity, we will maintain our focus on this group of metallic materials. To capitalize on the knowledge gained in the implementation of this research program, a real load-bearing graded-density bone substitute, such as a cervical anterior implant, will be designed, manufactured and in-vitro tested using the obtained bench-marking SLM process parameters.The results of this project, aimed at the combination of the novel additive manufacturing technologies and the high performance materials and structures, will promote the successful application of the next-generation FGM/S in medicine, and, potentially, in aerospace. Finally, the proposed program will contribute to the training of highly qualified personnel and attract top-level foreign students to Canada. They will have access to innovative technology and cutting-edge expertise in the fields of materials and novel forming processes, and will be trained within a multidisciplinary approach (materials science, metallurgy, and mechanical engineering). This enriched training will give the participating students and research personnel a competitive edge, as Canada’s booming health technology and aerospace industries are increasingly seeking personnel with this type of training.