Size effect due to contour laser scanning in 316L stainless steel produced by laser powder bed fusion

Abstract

In this work, effect of sample size on mechanical properties in the net-shaped 316 L alloys produced by laser powder bed fusion (LPBF) was studied. Tensile specimens with four different geometries, having the same total cross-sectional areas but with different tension beam widths of 0.75, 1.5, 3 and 6 mm, were produced by the LPBF and subjected to the tests. The experimental results indicated that there is a strong influence of the sample size of the mechanical properties in the as-built state. The yield strength increased and the ductility decreased pronouncedly with decreasing the sample size. Fine grain structures near the surface of the net-shaped samples due to the additional laser contour scanning is believed to be responsible to the strong sample size effect. The experiments also revealed that the sample size effect can be effectively reduced with the annealing heat treatments. The local strength of the fine-grained area near the surface was quantitatively characterized by an inverse finite element analysis. The local strength near the surface was found stronger in the direction parallel to the LPBF building direction than in the direction parallel to the LPBF transverse direction, leading to more significant size effect along this direction.

Keywords

• Additive manufacturing
• 316L stainless steel
• Laser powder bed fusion
• Contour scanning
• Size effect