Understanding Subsurface Behavior and Defect Formation During Laser Material Interactions Via Coupled In Situ X-Ray and Optical Probes

Nicholas Calta | 21-ERD-008

Project Overview

Laser-material processing is of increasing use in metal manufacturing, with applications in both additive and subtractive manufacturing techniques. There are many fundamental questions about the behavior of materials as a result of the laser-material interaction that is central to these manufacturing methods. These questions must be answered to enable a science-based paradigm for accelerated qualification and certification of parts produced by both additive and subtractive laser processes. This project used in situ synchrotron X-ray imaging and diffraction to study subsurface behavior in both metal additive manufacturing (AM) and laser drilling to address some of these questions. Our approach was divided into three areas. First, we collected time-resolved X-ray imaging data simultaneously with both optical and acoustic process monitoring data streams to identify signatures of defect formation during metal AM. Second, we performed systematic X-ray imaging and diffraction investigations studying how changing thermal fields influence the metal AM process. This included both tailoring the profile of the laser heat source and building multiple layer prints to probe microstructure evolution due to cyclic heating. Third, we used X-ray imaging to quantify material removal mechanisms during laser drilling of high aspect ratio holes.

From the first task, we identified a sensor fusion approach that can produce high quality predictions of pore formation events using acoustic and thermal emission data that can be detected by low-fidelity sensors that could be deployed to any commercial machine. As part of the second task, we collected data that measured fluid flow during laser melting of both elliptical and round Gaussian beam profiles of the process laser. For the third effort, we identified new material removal mechanism due to subsurface fluid flow that had not been previously observed during laser drilling. This mechanism helps to explain how drilling behavior observed with optical imaging at the workpiece surface translates to drilling further down underneath the workpiece surface. These observations were correlated to thermal emission sensors which could provide a route to process monitoring during laser drilling.

Mission Impact

This effort has further developed our scientific understanding of laser-material interactions central to metal fabrication approaches. Deep scientific understanding of laser-based additive and subtractive manufacturing approaches are a crucial component of LLNL's Core Competency in Advanced Materials and Manufacturing. This project has provided the detailed understanding required to develop science and technology tools and capabilities to meet future national security challenges.

Publications, Presentations, and Patents

Nicholas Calta, "Linking Laser Melting Phenomena to Process Monitoring Signatures with X-Ray and Optical Imaging" (Presentation, TMS Annual Meeting, Anaheim, CA, February 28, 2022).

———. 2022b. "Using Process Monitoring Signals to Identify Defects during Laser Powder Bed Fusion" (Presentation, Solid Freeform Fabrication Symposium, Austin, TX, July 25, 2022).

———. 2023. "Studying Laser Powder Bed Fusion Additive Manufacturing with High Speed Radiography at the Stanford Synchrotron Radiation Lightsource" (Presentation, Stanford Synchrotron Radiation Lightsource Beamline Review Meeting, Stanford, CA, March 29, 2023). 

Sanam Gorgannejad, "Process Monitoring for Pore Detection Using in Situ X-Ray Imaging and Diagnostic Signals" (Presentation, Solid Freeform Fabrication Symposium, Austin, TX, July 27, 2022). 

———. 2022b. "Process Monitoring for Pore Detection Using in Situ X-Ray Imaging and Diagnostic Signals" (Presentation, the International Conference on Additive Manufacturing, Orlando, FL, November 3, 2022).

———. 2023. "Multimodal Process Monitoring to Predict Outcomes during Laser Powder Bed Fusion" (Presentation, Solid Freeform Fabrication Symposium, Austin, TX, August 16, 2023). 

Gorgannejad, Sanam and Nicholas Calta. 2023." Automated Analysis of Synchrotron X-Ray Images for Laser-Based Processing Techniques: Feature Extraction, Quantification, and Tracking." Record of Invention IL-13837. Lawrence Livermore National Laboratory, Livermore, CA.

Gorgannejad, Sanam, Aiden A. Martin, Jenny Wang, Jean-Baptiste Forien, Maria Strantza, Peiyu Quan, Sen Liu, Vivek Thampy, Christopher J. Tassone, and Nicholas P. Calta. 2023. "Understanding Subsurface Behavior during Metal Laser Drilling Process via In-Situ Synchrotron X-Ray Imaging." In CLEO 2023, AM4R.2. Technical Digest Series. San Jose, CA: Optica Publishing Group. https://doi.org/10.1364/CLEO_AT.2023.AM4R.2.

Guss, Gabe, and Aiden Martin. 2022. "Scanner Controller (LLNL-CODE-841915)." Lawrence Livermore National Laboratory. 

Martin, Aiden, "Revealing Laser-Metal Interaction Dynamics During Additive Manufacturing Using High-Speed X-Ray Imaging" (Presentation, Denver X-ray Conference, virtual, August 2, 2021). 

Martin, Aiden A., Jenny Wang, Philip J. DePond, Maria Strantza, Jean-Baptiste Forien, Sanam Gorgannejad, Gabriel M. Guss, et al. 2022. "A Laser Powder Bed Fusion System for Operando Synchrotron X-Ray Imaging and Correlative Diagnostic Experiments at the Stanford Synchrotron Radiation Lightsource." Review of Scientific Instruments 93 (4): 043702. https://doi.org/10.1063/5.0080724.