Ultrasonic vibration-assisted laser engineered net shaping of Inconel 718 parts: Effects of ultrasonic frequency on microstructural and mechanical properties

Laser additive manufacturing (LAM) becomes a competitive method in fabricating Inconel 718 (IN718) parts in recent years. Among different LAM processes, laser engineered net shaping (LENS) has small substrate deformation, unique advantages of part remanufacturing capability, high part building efficiency, and high efficiency of powder utilization. LENS of IN718 is receiving extensive research and industrial applications. However, several problems (e.g. heterogeneous microstructures, internal cavities, and large porosity) still exist in LENS-fabricated IN718 parts. To reduce these problems, ultrasonic vibration-assisted (UV-A) LENS has been developed based on ultrasonic vibration's actions in materials melting and solidification processes. This process has been proven to be an effective manufacturing method in fabrication of IN718 parts. As one of the basic parameters of ultrasonic vibration, ultrasonic frequency will greatly influence the UV-A LENS processes, since it significantly affects ultrasonic vibration-induced two nonlinear effects (including cavitation and acoustic streaming) in materials melting and solidification processes. The influences of ultrasonic frequency in UV-A LENS processes are still unknown. The effects of ultrasonic frequency on microstructural properties (such as grain sizes, phase composition, precipitated phase morphology, bonding interface, and porosity) and mechanical properties (including microhardness, wear rate, and elastic modulus) of UV-A LENS fabricated IN718 parts are studied in this investigation. With the ultrasonic frequency increasing in UV-A LENS, the grain size is decreased, Laves phase is changed from long-bar columnar shape to particle shape, the bonding interface becomes smoother, the porosity is increased, the microhardness is increased, and the elastic modulus is decreased.