Ultrasonic Scattering Inspection Approach for Improved Methods of Additive Manufacturing

DOE is seeking methods to improve manufacturing of small modular reactors. Additive Manufacturing (AM) processes are desirable given the limited production basis and high quality necessary for nuclear components. Techniques to decrease the schedule of manufacturing and increase the confidence of the part’s microstructure are sought. Current inspection methods to maintain production speed and efficiency are lacking. To address this critical need, we a model- based ultrasonic scattering technique (UST) that qualifies witness coupons independent of the additive manufacturing method. The UST is microstructure-sensitive, which facilitates normalization across various AM methods and provides detailed information about material properties and performance. The witness coupon is a sample of simple geometry built alongside the component of interest in order to characterize the process at every build. By evaluating the microstructure post-process, the need for further heat treatment can be assessed. When parts are qualified for service, unnecessary heat treatment and processing can be avoided which will reduce the overall time and cost of manufacturing while guaranteeing quality and performance. The UST system consists of a focused immersion ultrasonic probe paired with a high-precision scanning system. At each scanning position, as the ultrasonic wave propagates, reflects and scatters through the microstructure of the AM part, the received signals contain encoded information about internal features. Analytical models and advanced signal processing algorithms are used to translate ultrasonic scattering data to spatial maps of microstructural parameters such as grain size, modulus, presence of heterogeneities (including porosity), and residual stress. The focus of the Phase I program is to demonstrate the feasibility of the ultrasonic scattering technique in characterizing microstructure and material properties for components made with varying additive manufacturing parameters, which will serve to determine whether heat treatment and/or additional processing is necessary. This outcome will lay the groundwork for optimizing the process monitoring technique for large scale inspections that guarantee the component reliability. Phase I efforts will concentrate on optimizing analytical models to account for microstructures found in AM parts and experimentally evaluating the validity of such models. By the end of Phase I, components made with various process parameters that induce mechanical and microstructural variability will be fully characterized using the UST and validated through traditional destructive testing. Commercial Applications and Other Benefits: In Phase II, BTC will focus on refining the electronics and data processing algorithms in the prototype, optimizing the sensitivity, and testing components of different feedstock types and power sources. For Phase III, BTC will package the system/software to accommodate large volume production and ensure suitability for defense and industry partners. The final product will serve as a qualification technique of AM parts and systems.