Ultrasonic Properties of Multi-material SS420-IN718 Structures Fabricated Using Laser Directed Energy Deposition

This article reports on the ultrasonic properties of the compositionally graded structures with discrete composites of stainless Steel 420 and Inconel 718 with different weight fractions. Samples with specific weight fractions were fabricated and tested using ultrasound to measure the ultrasonic velocity and attenuation coefficient. The velocities were further used to calculate the leading diagonal of the stiffness matrix, which showed anisotropy. To further quantify the anisotropy and compare the sample quantitatively, an anisotropy index was defined. A simple rule of mixture was also used to compare the trends between elastic constants and weight fraction. Similarly, the attenuation coefficient was compared for different compositions. The results suggest that the addition of IN718 increases the anisotropy and attenuation coefficient of the acoustic waves. Interestingly, the anisotropic index was highest for the \(25\%, 50\%, 100\%\) $25\%,50\%,100\%$ IN718 samples and followed no particular monotonic trend. Similarly, the attenuation coefficients of \(25\%, 50\%\) $25\%,50\%$ were higher than rest of the mixtures with no monotonic trend. The results suggest that the presence of IN718 plays a big role in the solidification and the resulting microstructure, which further creates anisotropy in the sample, and increases the attenuation of the sample as well. This points toward multiphase contribution towards velocity, elastic constants and attenuation of acoustic waves.