Ultrasonic measurements to differentiate hybrid processes in additively manufactured 316L stainless steel

Hybrid additive manufacturing (AM) generates materials with spatial variations by integrating additional manufacturing processes, such as milling, laser peening, or ultrasonic peening, at specific locations during the fabrication process. These material variations encompass alterations in average grain size, dislocation densities, and the introduction or alleviation of residual stresses. Importantly, these property changes extend beyond the applied layer, exhibiting a cumulative impact on preceding layers. The specifics of each hybrid process have been shown to improve mechanical properties, thereby enhancing the performance of components. However, there are distinctive challenges associated with the nondestructive validation of such samples. Traditional ultrasonic techniques have proven effective in mapping material variations with satisfactory spatial resolution in hybrid components. In this study, ultrasonic responses, i.e., wave speed, attenuation, and diffuse backscatter measurements, are used to differentiate between three different hybrid processes (milling, laser peening, and ultrasonic peening) in additively manufactured 316L stainless steel. This work is anticipated to impact the qualification of metal AM parts.