Repeatability of Residual Stress in Replicate Additively Manufactured 316L Stainless Steel Samples

Additive manufacturing presents an opportunity to produce complex component geometries with exceptional strength properties in 316L stainless steel. The high temperature gradients during manufacturing produce near-yield tensile residual stresses often near exterior component surfaces, which are indicative of the process history. In this study the repeatability of the residual stress is evaluated across five identically prepared, replicate samples sequentially built on a single 3D Systems ProX CMP200 machine with fixed process parameters. The samples are nominally cube shaped with edge lengths of 50.8 mm. Near surface residual stresses are measured using both strain gage hole-drilling and X-ray diffraction. Within the first 1 mm of the top surface, all measurements show equi-biaxial tensile residual stresses with peak magnitude near 500 MPa (close to yield strength). One build is found to be an outlier, with residual stress different than in the four other builds. Data from hole-drilling and X-ray based techniques are in general agreement. Among the four similar builds, average normal residual stress in the near-surface (0–0.25 mm depth) is 424–427 MPa and standard deviation of residual stress among the four builds is 25–39 MPa. Average residual stress in the mid-depth (0.25–0.90 mm depth) is 442–453 MPa and standard deviation is 8.8–8.9 MPa. While the high tensile near surface residual stress may be of concern (because of potential increased risk for subcritical cracking by fatigue or corrosion), variation of residual stress is small and similar to levels seen in other metallic forms such as plate or die forgings.