Electrical Discharge Machining of Biomedical Nitinol Alloys and the Resulting Fundamental Relationship of Microstructure-Property-Function

本提案的研究目的是通过汇集互补的国际研究和教育专业知识，了解生物医用镍钛合金的放电加工条件、白色层（即重铸层）与疲劳和腐蚀之间的基本关系。它将测试的假设，放电加工使用最小的放电能量是一个非常有竞争力的过程相比，机械加工，以经济地制造精细的无毛刺镍钛合金微结构，高纵横比和优良的表面光洁度。研究方法是：（1）探索医用镍钛合金电火花加工的工艺能力，建立加工条件与表面完整性之间的基本关系：（2）用透射电镜和X射线衍射确定白色层是否为亚稳纳米准晶;（3）阐明工艺诱导的表面完整性，特别是白色层，对疲劳和腐蚀性能的基本作用;以及（4）通过具有材料烧蚀能力的多物理过程模拟方法，揭示放电过程中材料的烧蚀机理和微观结构演变，研究成果将具有重要意义。对包括钛、铬镍铁合金、不锈钢和硬化合金在内的各种其他难切削材料的加工具有广泛的影响。金属生物材料电火花加工的良好可持续实践可以为生物医学设备行业以及工具、燃气涡轮机、化学和石油行业带来商业价值。该项目将在亚拉巴马大学和亚琛大学之间建立一个协同教育网络，以培养下一批？全脑？学生在全球范围内。该合作网络还将为从基础研究到工业实践的快速技术转移提供快速途径。

The research objective of this proposal is to understand the basic relationship between machining conditions, white layer (that is, recast layer), and fatigue and corrosion by electrical discharge machining of biomedical Nitinol alloys by bringing together complementary international research and education expertise. It will test the hypothesis that electrical discharge machining using minimum discharge energy is a very competitive process compared to mechanical machining to economically fabricate delicate burr-free Nitinol microstructures with high aspect ratio and excellent surface finish. The research approaches are to: (1) explore the process capability in electrical discharge machining of biomedical Nitinol alloys to establish a basic relationship between processing conditions and surface integrity; (2) determine whether the white layer is metastable nano-quasicrystal using transmission electron microscopy and x-ray diffraction; (3) clarify the fundamental role of process-induced surface integrity, white layer in particular, on fatigue and corrosion performance; and (4) reveal material erosion mechanism and microstructural evolution in electrical discharging via a multiphysics process simulation approach with the capability of material ablation.The research results will have a wide spectrum of impacts on machining of a broad range of other difficult-to-cut materials including titanium, Inconel, stainless steel, and hardened alloys. The sound sustainable practices in electrical discharge machining of metallic biomaterials can bring business value to biomedical device industry as well as tool, gas turbine, chemical and oil industries. The project will establish a synergistic education network between the University of Alabama and Aachen University to train the next cadre of ?whole-brain? students in the global context. The collaborative network will also provide an express way for fast technology transfer from fundamental research to industrial practices.