Effect of Build Orientation on the Fatigue Behavior of Stainless Steel 316L Manufactured via a Laser-Powder Bed Fusion Process

Shrestha, Rakish
Simsiriwong, Jutima
Shamsaei, Nima
Thompson, Scott M.
Bian, Linkan
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University of Texas at Austin

n this study, the effects of build orientation on the mechanical properties and fatigue life of stainless steel (SS) 316L, fabricated using the Laser-Powder Bed Fusion (L-PBF) additive manufacturing (AM) process, were investigated under monotonic tensile and uniaxial strain-controlled fully-reversed (R = -1) cyclic loadings. Tensile tests were conducted at a strain rate of 0.001 s-1 , while fatigue tests were performed at strain amplitudes ranging from 0.1% to 0.4% at various frequencies to have a nearly consistent average strain rate in all tests. The comparison between the tensile properties of additively manufactured and wrought SS 316L revealed that L-PBF specimens exhibited higher yield and ultimate tensile stresses as compared to the wrought specimen. In addition, the elongation to failure of the wrought specimen was similar to that of the horizontally oriented specimen, while it was lower relative to specimens built in vertical and diagonal directions. From the strain-life fatigue analysis, the diagonally oriented L-PBF specimens generally exhibited lower fatigue strength as compared to vertical and horizontal specimens. The fractography analysis revealed three major types of defects to be responsible for the crack initiation and failure. These included (1) voids formed due to lack of fusion between the subsequent layers and entrapped gas, (2) inclusions formed due to the partially melted powder particles, and (3) un-melted powder particles clustered near a void.