Measuring the Cooling Behavior of Melt Pools in L-PBF by Pyrometry

Area of Science:

• Materials Science
• Additive Manufacturing
• Optical Diagnostics

Background:

• Accurate temperature measurement is crucial for Laser Powder Bed Fusion (L-PBF) process control.
• Understanding cooling dynamics in L-PBF is essential for predicting material microstructure and properties.
• Pyrometry offers a non-contact method for in-situ temperature monitoring during L-PBF.

Purpose of the Study:

• To measure cooling durations of single laser tracks in L-PBF using pyrometry.
• To determine the emissivity of 30CrMoNb5-2 alloy for accurate temperature measurements.
• To validate a new fitting method for distorted pyrometer signals and analyze microstructural changes.

Main Methods:

• In-situ emissivity determination of 30CrMoNb5-2 alloy using pyrometry and thermocouples.
• Verification of one-color and two-color pyrometer precision in the L-PBF system.
• Application of a novel signal fitting method to analyze pyrometer data from single laser tracks.
• Electron Backscatter Diffraction (EBSD) analysis of melt pool microstructures.

Main Results:

• Emissivity of 30CrMoNb5-2 alloy was determined in-situ, enabling accurate temperature readings.
• A new fitting method successfully corrected for signal distortions caused by smoke and weld beads.
• Cooling durations were correlated with observed microstructural features, including deformation and amorphization.
• Experimental cooling durations provide data for validating L-PBF simulations.

Conclusions:

• Pyrometry, with in-situ emissivity calibration and advanced signal processing, is effective for measuring cooling durations in L-PBF.
• Measured cooling durations directly correlate with microstructural evolution, offering insights into material behavior.
• The findings facilitate improved L-PBF process control, simulation validation, and microstructure-property relationship studies.