Cyclic Plastic Material Behavior of 316l, Manufactured by Laser Powder Bed Fusion (Pbf-Lb/M)

Abstract

In laser powder bed fusion (PBF-LB/M), the influence of laser parameters on the static mechanical properties is well known. Different laser parameters result in a higher or a lower tensile strength. Only little is known about the influence of the laser parameters on the cyclic plastic behavior at high strain amplitudes. Different laser parameters may result in a significant change of the stress levels during cyclic loading. In this study the cyclic plastic material behavior at high strain amplitudes of up to 3.0 % of AISI-316L manufactured by PBF-LB/M is investigated. Two different laser parameter sets are applied. One laser parameter set is outside the stable melting zone and the other one is inside the stable melting zone according to [1] . Metallographic analyses and static, as well as strain-controlled fatigue tests were conducted. Strain-controlled fatigue testing of the specimens in the low-cycle fatigue range (R= -1) allows the specific cyclic material behavior to be evaluated and, for strain amplitudes greater than 2.5 %, to be reasoned with twin-induced strain hardening. A correlation between the twin-induced strain hardening behavior and the resulting maximum stress curve per endured cycle is observed. The plastic material behavior is dominated by softening, which is reduced with increasing strain amplitude due to mechanical twinning. Finally, the strain-life curve is determined and approximated by the Manson-Coffin fatigue parameters. It is shown, that the porosity highly affects the fatigue life. Additionally, the laser parameters influence the generated stress level during cyclic plastic loading.

Keywords: Laser powder bed fusion, 316L, Low-cycle fatigue, Strain-controlled fatigue testing, Strengthening mechanisms