Surface Characterization of Laser Powder Bed Fusion for Melting Mode Determination

Abstract

<title>Abstract</title> The top surface of an additively manufactured part contains information about the most recently deposited layer but also preserves data about the layers preceding it. In laser powder bed fusion (L-PBF), the choice of process parameters significantly influences laser track consistency and impacts layer uniformity. As successive layers build upon each other, the surface becomes indicative of overall part quality, parameter effectiveness, and melting behavior. This research establishes key metrics that relate surface topology and melting behavior through comprehensive characterization of as-built L-PBF specimen surfaces using techniques that extend beyond simple summarization parameters like average roughness. Confocal laser scanning microscopy is employed to visualize 3-D height maps and quantify surface morphology using fast Fourier transforms (FFT). Furthermore, internal features are evaluated through relative density measurements obtained via metallographic methods, and microstructural analysis is conducted using electron backscatter diffraction. The results demonstrate the ability of surface features at different length scales to indicate part quality and melting behavior. FFTs are able to identify periodic surface characteristics, which correspond to high and low input energy melting, and can be used to distinguish between parts possessing similar summary surface parameters. Additionally, microscale laser path ripple angles are measured and shown to correlate to much broader process health metrics and melt pool behavior. The quantitative analysis employed using the FFT and laser path ripple angle provide novel methods for surface characterization that extend past the use of conventional summary parameters.

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