Evaluating effects of microstructure and porosity on elastic anisotropy of additively manufactured materials using ultrasonic techniques

The potential of additive manufacturing is often limited by qualification issues, particularly due to process defects such as lack-of-fusion porosity and highly 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 various process parameters and heat treatments (HTs) on the elastic anisotropy of laser powder bed fusion 316 L 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, HTs 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 findings of this research highlight the potential of ultrasonic techniques for monitoring and qualifying additively manufactured materials.