Anisotropy of Mechanical Properties and Residual Stress in Additively Manufactured 316L Specimens.

Alexey Fedorenko,Evgeny Lomakin,Iskander Akhatov,Oleg Staroverov,Mikhail Tretyakov,Stanislav Evlashin,Boris Fedulov,Yulia Kuzminova

doi:10.3390/ma14237176

Abstract

In the presented study, LPBF 316L stainless steel tensile specimens were manufactured in three different orientations for the analysis of anisotropy. The first set of specimens was built vertically on the build platform, and two other sets were oriented horizontally perpendicular to each other. Tensile test results show that mean Young’s modulus of vertically built specimens is significantly less then horizontal ones (158.7 GPa versus 198 GPa), as well as yield strength and elongation. A role of residual stress in a deviation of tensile loading diagrams is investigated as a possible explanation. Simulation of the build process on the basis of ABAQUS FEA software was used to predict residual stress in 316L cylindrical specimens. Virtual tensile test results show that residual stress affects the initial stage of the loading curve with a tendency to reduce apparent Young’s modulus, measured according to standard mechanical test methods.

Highlights

The application of laser powder bed fusion (LPBF) in industry is an opportunity to produce lightweight customized structures of complex shape with exceptional mechanical performance
In the presented study, LPBF 316L stainless steel tensile specimens were manufactured in three different orientations for the analysis of anisotropy
Virtual tensile test results show that residual stress affects the initial stage of the loading curve with a tendency to reduce apparent Young’s modulus, measured according to standard mechanical test methods

Summary

Introduction

The application of laser powder bed fusion (LPBF) in industry is an opportunity to produce lightweight customized structures of complex shape with exceptional mechanical performance. The effect of modulus decrease in build direction was observed in [11] for the IN738LC superalloy, and authors extracted crystallographic texture from electron backscatter diffraction in order to estimate Young’s modulus using Voigt, Reuss and Hill’s methods [12] Another microstructural explanation of anisotropy accompanied by higher mechanical properties in the horizontal direction in terms of grain aspect ratio and orientation is presented in [13]. Röttger et al [15] studied vertically and horizontally oriented 316L specimens built with different process parameters, and while the reduction of Young’s moduli in comparison with conventional steel was observed in many cases, they indicate neither texture nor porosity as the only dominant factor. The relative porosity of produced parts analyzed with the optical microscope Axio Scope.A1 (Carl Zeiss, Jena, Germany), according to ASTM E1245, does not exceed 0.1%

Tensile Tests

Findings

Validation Experiment