A physical framework linking ultrasonic scattering to strain localization in additively manufactured alloys.

Advancements in additive manufacturing (AM) have created a strong demand for the qualification of metal alloys used in critical structural components. Ultrasound offers a promising non-destructive technique for analyzing mechanical properties from the complex and diverse microstructural features of AM materials. Targeting the physical mechanism from ultrasound to mechanical properties, we introduce a quantitative measure of microstructural inhomogeneity derived from parameterizing microstructural features. This inhomogeneity by inducing strain localization and the subsequent accumulation of geometrically necessary dislocations (GNDs), governs the material deformation. We demonstrate that this same inhomogeneity parameter also indicates the degree of ultrasonic attenuation. This establishes a direct, physical link between the elastodynamic response (attenuation) and the core plastic mechanism (GND accumulation), which ultimately determines material strength. Furthermore, we show numerically that the same inhomogeneity descriptor governs ultrasonic attenuation across materials belonging to different crystal systems, and we validate experimentally its effectiveness in predicting the relative strength of LPBF-fabricated SS316L, SS17-4PH and pure titanium. The full mechanistic chain linking attenuation to GND accumulation is established experimentally for LPBF SS316L, while its extension to other crystal systems is supported by simulation and requires material-specific calibration. These findings reveal the physical mechanism underlying the experimentally observed correlation between ultrasonic attenuation and mechanical strength in AM materials, enabling new framework for ultrasonic applications and enhancing the safety and reliability of AM alloys in critical structural components.