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In-process Precipitation During Laser Additive Manufacturing Investigated by Atom Probe Tomography

Laser Metal Deposition (LMD) is a specific Laser Additive Manufacturing (LAM) process in which a focused laser beam creates a melt pool in the component’s surface. Metallic powder is then injected through a nozzle into the melt pool. As neighboring tracks and subsequent layers are deposited during the LMD process, already consolidated material experiences a cyclic re-heating. This intrinsic heat treatment (IHT) can be used to trigger the precipitation reaction in precipitation hardening alloys [1]. We used the rapid alloy prototyping capabilities of the LMD process to efficiently screen different alloy compositions by producing compositionally graded samples. In a simple model maraging steel containing 19at% Ni, we varied the Al concentration from 0 to 25at% to identify an alloy composition that responds well to the IHT of the LAM process to produce an in-process precipitation strengthened maraging steel. Due to its sub-nanometer resolution, Atom Probe Tomography (APT) provides compositional information at high-resolution and is therefore ideally suited for analyzing small clusters and precipitates. Additionally, we used High Energy Synchrotron X-Ray Diffraction (HEXRD) to provide crystallographic information with high sensitivity.