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

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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.