CAREER: The Science of Producing Metallic Parts with Location-Specific Properties Using Additive Manufacturing

金属增材制造是一层一层地制造零件，可以实现具有巨大几何复杂性和局部变化微观结构的零件。虽然局部微观结构的预测和控制，使局部材料特性的控制，有可能实现整体结构内的复杂功能，但在金属增材工艺中尚未完全实现。实现这种能力被视为实现组件的重要一步，通过单一的制造过程，可以模仿有利的生物启发结构，如螳螂虾爪，结合了非常坚硬的外表面和坚韧的核心，具有出色的抗断裂性。该学院早期职业发展（Career）计划奖旨在通过了解增材制造工艺参数如何驱动关键微观结构特征的变化，从而解决这一知识差距，从而改变印刷镍钛形状记忆合金的最终性能。能够预测和控制特定位置的材料性能将极大地扩展当前的增材制造能力，为参与航空航天和生物医学行业高端部件生产的美国制造商提供进一步的竞争优势。该奖项还将通过以下活动为未来制造业劳动力的发展提供机会；1)为劳伦斯利弗莫尔国家实验室的研究生提供实习机会；2)海外学习项目；3)为K-12教师提供拓展项目；4)将增材制造课程纳入针对德克萨斯州先进制造业劳动力的大型证书项目。研究目标是利用激光粉末床融合增材制造工艺制造具有特定位置性能的金属结构。重点研究了镍钛合金的相变温度随加工条件的变化规律。初步研究表明，影响相变温度的主要因素有三个；(1)析出相的体积分数，(2)材料内部的位错密度，(3)加工过程中镍的蒸发损失。实验测试和随后的表征将对这些因素的影响进行反卷积。最重要的是，这些结果将考虑到加工条件，并将提供如何选择工艺参数（如舱口间距和激光功率影响）来控制微观结构的见解。镍钛被选为其他材料的替代品，其中微观结构和/或成分的变化会极大地影响材料的性能，因为它对这些变化很敏感。预计本CAREER研究中产生的知识将作为基础知识，用于在使用金属增材制造加工的其他材料系统中实现特定位置的性能控制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Metal additive manufacturing, where the part is built up layer by layer, can realize parts with great geometrical complexity and with locally varying microstructures. While prediction and control of local microstructures, enabling the control of local material properties, has the potential to realize complex functionalities within monolithic structures, it is not yet fully realized in metal additive processes. Achieving this capability is seen as an important step in realizing components, via a single manufacturing process, that can mimic advantageous bioinspired structures such as a mantis shrimp claw which combines a very hard outer surface with a tough core to give excellent fracture resistance. This Faculty Early Career Development (CAREER) Program award seeks to address this knowledge gap by understanding how additive manufacturing process parameters drive changes in pivotal microstructure characteristics, and hence the final properties, of printed nickel-titanium shape memory alloys. Being able to predict and control location-specific material properties will greatly extend current additive manufacturing capabilities giving further competitive advantage to US manufacturers involved in the production of high end components for aerospace and biomedical industries. This award will also provide opportunities for future manufacturing workforce development through activities such as; 1) internships for graduate students at Lawrence Livermore National Laboratory, 2) study abroad programs, 3) an outreach program for K-12 teachers, and 4) incorporation of a course on additive manufacturing into a larger certificate program aimed at the advanced manufacturing workforce in Texas. The research objective is to enable the fabrication of metallic structures with location-specific properties using laser powder bed fusion additive manufacturing processes. The focus of the research is on how the phase transformation temperature of nickel-titanium alloys varies with processing conditions. Preliminary work suggests that there are three significant factors affecting the transformation temperature; (1) the volume fraction of precipitates, (2) the dislocation density within the material, and (3) the nickel evaporation loss during processing. Experimental tests and subsequent characterization will deconvolve the effects of these factors. Most importantly the results will be considered with respect to the processing conditions and will provide insights on how process parameters such as hatch spacing and laser power influence can be selected to control the microstructure. Nickel-titanium is selected as a proxy for other materials in which microstructural and/or composition changes greatly affect material properties, due to its sensitivity to these changes. It is expected that the knowledge generated in this CAREER research will serve as foundational knowledge to realize location-specific property control in other material systems processed using metal additive manufacturing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.