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

金属加工法是一种将零件层层堆积起来的制造方法，可以制造出几何形状复杂、显微组织局部变化的零件。虽然局部组织的预测和控制能够实现局部材料性能的控制，但在金属添加剂工艺中还没有完全实现。实现这一能力被视为通过单一制造工艺实现部件的重要一步，该部件可以模仿有利的生物灵感结构，如螳螂虾爪，它将非常坚硬的外表面和坚韧的核心结合在一起，提供出色的抗断性。该学院早期职业发展(Career)计划奖项旨在通过了解添加剂制造工艺参数如何驱动印刷镍钛形状记忆合金的关键微结构特征以及最终性能的变化来解决这一知识差距。能够预测和控制特定地点的材料性能将极大地扩展当前的添加剂制造能力，为参与航空航天和生物医药行业高端零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的制造业劳动力发展提供机会：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)出国留学计划，3)为K-12教师提供外展计划，以及4)将添加剂制造课程纳入针对德克萨斯州先进制造业劳动力的更大证书计划。研究的目标是使用激光粉末床熔化添加剂制造工艺来制造具有特定位置特性的金属结构。研究的重点是镍钛合金的相变温度随工艺条件的变化。初步工作表明，影响相变温度的主要因素有三个：(1)析出物的体积分数；(2)材料内部的位错密度；(3)加工过程中的镍蒸发损失。实验测试和随后的表征将去卷积这些因素的影响。最重要的是，结果将考虑到加工条件，并将提供关于如何选择工艺参数，如舱口间距和激光功率影响，以控制微观结构的见解。由于镍钛对这些变化的敏感性，它被选作其他材料的替代物，在这些材料中，微观结构和/或成分的变化对材料性能有很大影响。预计在这项职业研究中产生的知识将作为基础知识，在使用金属添加剂制造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NSF的法定使命，并通过使用基金会的智力优势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.