Mechanical properties of biomedical 316L stainless steel plates with in-plane orthogonal anisotropy by aligning crystallographical orientation via additive manufacturing

Abstract

Low stiffness in the axial direction is required to suppress stress shielding, whereas high stiffness in the torsional direction is required to promote bone healing in metallic implants. Therefore, two types of 316L stainless steel additive manufactured plates having a low Young’s modulus in the longitudinal direction and high Young’s modulus in the lateral direction were fabricated via selective laser melting. Their crystallographic orientations were tried to be controlled being <100>/<110> and <110>/<111> along two in-plane orthogonal directions. Although the degrees of <110> orientations perpendicular to the laser scanning direction and parallel to the stacking direction were slightly reduced, a strong <100> orientation was obtained parallel to the laser scanning direction. Therefore, the additive manufactured plates with the Young’s modulus higher in the lateral direction than that in the longitudinal direction could be obtained successfully. However, with regard to the directions along <100> and <111> orientations, the difference in Young’s modulus between the additive manufactured plates and the single crystal were more than 30%. This difference can be decreased by optimizing the fabrication parameters for selective laser melting and changing the building direction. On the other hand, many similar aspects could be observed between the plastic deformation behaviors of additive manufactured plates fabricated in this study and that of single crystal reported in the literature. However, the microstructure of additive manufactured plates was heterogeneous, containing equiaxed and columnar grains, depending on the laser scanning direction and stacking direction. Therefore, the strength and ductility of additive manufactured plates were probably affected by not only crystallographic orientation but also the relationship between tensile loading direction and crystal grain morphology.

Keywords

• additive manufactureing
• 316l stainless steel
• crystallografical orientation
• mechcanical properties
• young’s modulus
• anisotropy