Ultrasonic Nondestructive Evaluation of Critical Multimaterial Interfaces

Systems and components comprised of multiple materials have engineering advantages over single material systems, as they allow for complex geometries and enable custom physical, structural, chemical, electromagnetic, and thermal properties. Thus, the ability to evaluate the integrity of critical interfaces between disparate materials is essential for the qualification of multimaterial systems. Ultrasonic nondestructive evaluation (NDE) uses high-frequency sound waves to detect defects and characterize material properties in a component without needing to cut it open, which is especially useful for multimaterial systems, in which defects can be located inside the part and accumulate at the critical multimaterial interface. The objective of this work is to apply ultrasonic NDE to quantify defects and material properties and qualify critical interfaces in multimaterial components and systems. Grounded in ultrasonic wave propagation theory, applications for electronic packaging as well as structural metal and polymer additive manufacturing were considered. Therefore, models describing ultrasonic beam propagation and material property relationships to ultrasonic responses were leveraged to assess fluid, polymer, and metal material properties as well as fluid-solid, solid-powder, and dissimilar solid interfaces. First, ultrasonic NDE was successfully used to efficiently and noninvasively monitor the degradation of coolants and thermal interface materials (TIMs) in immersion cooling systems. Next, an 800 µm spherical internal structure inside a SS316L additively manufactured (AM) cube was successfully resolved using ultrasound, demonstrating the potential to leverage AM to manufacture custom standard samples with realistic defects to calibrate NDE modalities. Finally, NDE of a layered multimaterial AM cube in two orientations revealed high spatial variability at the dissimilar material interfaces, indicating probable air gaps and delaminations between the layers of disparate materials, and anisotropy in the wave speed between the build and transverse directions was identified. This work demonstrates the power of ultrasonic NDE to detect defects and characterize materials in multimaterial systems.