Linear and Nonlinear Ultrasonic Evaluation of Elastic Properties and Microstructure of Laser Powder Bed Fusion 316L Stainless Steel
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Herburger, Daniel
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Abstract
The potential of additive manufacturing is often limited by qualification issues, particularly due to process defects such as lack-of-fusion porosity and unexpected anisotropic elastic properties. This research demonstrates the ability of ultrasonic measurement techniques to assess these elastic properties, process defects, and microstructural characteristics. Ultrasonic velocity measurements are used to evaluate the impact of varying process parameters and heat treatments on the elastic anisotropy of Laser Powder Bed Fusion 316L stainless steel. These variations are linked to material characteristics through microstructural analysis and porosity measurements. By characterizing the orthotropic elastic behavior, this study quantifies the errors that can arise in the design and analysis of additively manufactured parts by assuming isotropic or transversely isotropic elastic properties. Furthermore, heat treatments are used to isolate and quantify the individual contributions of process defects, such as lack-of-fusion defects, and microstructural factors, including crystallographic texture and grain morphology, to elastic anisotropy. The nonlinear ultrasonic measurement technique of Second Harmonic Generation is used to detect lack-of-fusion defects and provide insights on their orientation. The findings of this research highlight the potential of ultrasonic techniques for monitoring and qualifying additively manufactured materials.
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2024-08-19
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