Internal Stress Evolution and Subsurface Phase Transformation in Titanium Parts Manufactured by Laser Powder Bed Fusion—An In Situ X‐Ray Diffraction Study

Advanced engineering materials 23(11), 2001502 (2021). doi:10.1002/adem.202001502 special issue: "Neutrons and Synchrotron Radiation - Unique Tools for the Characterization of Materials"
Laser powder bed fusion (LPBF) is a metal additive manufacturing technology,which enables the manufacturing of complex geometries for various metals andalloys. Herein, parts made from commercially pure titanium are studied usingin situ synchrotron radiation diffraction experiments. Both the phase transformationand the internal stress buildup are evaluated depending on the processingparameters. For this purpose, evaluation approaches for both temperatureand internal stresses from in situ diffraction patterns are presented. Four differentparameter sets with varying energy inputs and laser scanning strategiesare investigated. A combination of a low laser power and scanning speed leads toa more homogeneous stress distribution in the observed gauge volumes. Theresults show that the phase transformation is triggered during the primarymelting and solidification of the powder and subsurface layers. Furthermore, thestress buildup as a function of the part height during the manufacturing processis clarified. A stress maximum is formed below the part surface, extending intodeeper layers with increasing laser power. A temperature evaluation approach forabsolute internal stresses shows that directional stresses decrease sharply duringlaser impact and reach their previous magnitude again during cooling.
Published by Deutsche Gesellschaft fu��r Materialkunde, Frankfurt, M.