Elastic Residual Strain and Stress Measurements and Corresponding Part Deflections of 3D Additive Manufacturing Builds of IN625 AM-Bench Artifacts Using Neutron Diffraction, Synchrotron X-Ray Diffraction, and Contour Method

Thomas H Gnaupel-Herold,Christopher R D’Elia,Darren C Pagan,Michael R Hill,Thien Q Phan,Bjorn Clausen,Adrian T Dewald,Donald W Brown,Maria Strantza,Lyle E Levine,Jarred Heigel,J Y Peter Ko

doi:10.1007/s40192-019-00149-0

Abstract

One of the primary barriers for adoption of additive manufacturing (AM) has been the uncertainty in the performance of AM parts due to residual stresses/strains. The rapid heating and cooling rates from the thermal history of the laser melting process result in high residual stresses/strains that produce significant part distortion. Efforts to mitigate residual stresses using post-process heat treatments can significantly impact the microstructures of the AM part which may lead to further issues. Therefore, the ability to accurately predict the residual stresses in as-built AM parts is crucial, and rigorous benchmark measurements are needed to validate such predictions. To fill this need, the AM-Bench aims to provide high-fidelity residual stress and strain benchmark measurements in well-characterized AM bridge-shaped parts. The measurements reported here are part of the residual elastic strain benchmark challenge CHAL-AMB2018-01-RS. Residual strains and stresses in this work were measured using neutron diffraction, synchrotron X-ray diffraction, and the contour method. Part deflection measurements were performed using a coordinate measurement machine after the part was partially separated from the build plate. These independently measured results show a high degree of agreement between the different techniques.

Highlights

The presence of high residual stress in engineering alloy components produced by additive manufacturing (AM) is one of the challenges that must be solved before wide spread adoption of AM
Vertical part deflections were measured using a coordinate measurement machine (CMM) after the legs are separated from the build plate
Residual stresses in the X direction were measured using the contour method for the part and build plate along three cross sections in the middle of legs 4, 7, and 10

Summary

Introduction

The presence of high residual stress in engineering alloy components produced by additive manufacturing (AM) is one of the challenges that must be solved before wide spread adoption of AM. Residual stresses and strains are inherently linked to the processing conditions. For the laser powder bed fusion (LPBF) process, the thermal gradients, cooling rates, and part mechanical constraints result in the multi lengthscale residual stresses that exist within the as-built part [1,2,3,4,5]. These stresses can affect the component life in service and cause a catastrophic failure during the build such as part separation from the build plate. A description of how these residual stress measurements fit into this larger picture is given in the leadoff article of this special issue [6]

Methods

Results

Conclusion