Session: 16-02-01: Microstructure II

Paper Number: 173778

Evaluation of Material Consolidation and Solidified Molten Pool Behavior Under Different Powder Layer Thicknesses for Nickel Alloy 718 in Pbf-Lb 

A fundamental but possibly insufficiently understood and characterized aspect of laser powder bed fusion (PBF-LB) metal based additive manufacturing is the relationship between the powder layer thickness, scanning conditions and the consolidation behavior of the molten pool within a layer. AM Bench is a NIST-led organization that provides a continuing series of AM benchmark measurements and challenge problems with the primary goal of enabling modelers to test their simulations against rigorous, highly controlled additive manufacturing benchmark measurement data. Part of this year’s AM bench challenge series expands upon prior challenges that used single laser tracks and/or bare substrates by adding complexities that better represent the PBF-LB process and provide broadly applicable benchmark data for PBF-LB simulation tools. This presentation will provide an overview of the measurement results from the AM-Bench 2025-06 challenge series characterizing the fused layer structures (surface and subsurface) of Inconel 718 tracks fabricated under three conditions: bare plate, 80 μm powder layer, and 160 μm powder layer. In these benchmark experiments, the primary laser parameters such as laser power, laser scan speed, laser spot diameter, and track-to-track (i.e., hatch) spacing were fixed. The pad geometries were 5 mm x 5 mm and 5 mm x 1 mm, providing evaluations that incorporate different residual heat effects during a typical PBF-LB build process. Three repeats for each condition were conducted for statistical significance. All PBF-LB experiments were produced using the Fundamentals of Laser-Material Interaction (FLaMI), which is a NIST-designed and built laser-processing metrology platform.

The pad surface topography challenge (CHAL-AMB2025-06-PST) provides detailed surface roughness and fused layer thickness measurements of different regions of the fabricated pads based on both areal and profile analysis. The 2.5D measurements of the surface topography of each sample were assessed using focus variation microscopy. For this challenge a definition of the fused layer thickness and new measurement technique are introduced to remove operator subjectivity, providing a robust quantitative evaluation based on bi-modal histogram analysis to improve model-measurement comparisons. In addition, the pad melt pool geometry (CHAL-AMB2025-06-PMPG) challenge includes cross-sectional melt pool measurements including bead height, width, depth, overlap depth and width at specified locations of all pads. Additional metrics from the cross-sections include the total solidified area above the substrate and the total dilution area below the substrate. In-situ measurements based on high-speed staring thermography providing location-specific liquid and solid cooling rates, and location specific time above melting will also be discussed. Finally, observations and trends regarding melt pool behavior under the investigated conditions will be presented and commentary on the agreement between measurement results and the predictions submitted by challenge participants will be discussed.

Presenting Author: Jesse Redford NIST

Presenting Author Biography: Jesse Redford is a Mechanical Engineer at the National Institute of Standards and Technology (NIST), where he works in the Intelligent Systems Division, Production Systems Group. His current research focuses on developing both in-situ and ex-situ metrology, test methods, and characterization techniques to improve model validation methodologies and aid the understanding and qualification of metal additive manufacturing parts, processes, and feedstock materials.

Authors:

Jesse Redford NIST
Jordan Weaver NIST
David Deisenroth NIST
Sergey Mekhontsev NIST
Brandon Lane NIST
Lyle Levine NIST