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Summary
Laser additive manufacturing (LAM), as an advanced additive manufacturing technology, has high efficiency and excellent precision in producing large size 3D printing elements. It has proven potential for application in buildings and civil infrastructure. However, in order to apply LAM technology to the production of components in civil engineering, it is necessary to understand comprehensively the mechanical properties of LAM products. In a previous study, the mechanical properties in the layer plane of LAM 316L stainless steels have been studied, but the mechanical properties in the building elevation plane are still unknown. To this end, an experimental study into the mechanical properties and microstructure of LAM 316L stainless steels has been undertaken and is reported in this paper. A total of 18 tensile coupons with two nominal thicknesses were extracted in various orientation angles relative to the print layer from the LAM prims for the uniaxial tensile tests. The influences of the orientation angle and thickness on the mechanical properties of LAM 316L stainless steels were investigated through the tensile tests. The test results show high anisotropy of the LAM 316L stainless steels in the building elevation plane, for which the anisotropy indexes of all mechanical properties exceed 10%, and the anisotropy indexes of the elastic modulus, Poisson's ratio and the proof stresses even exceed 25%. In addition, a very small Poisson's ratio value and an extreme short softening stage of stress-strain curves after peak values were identified for the coupons with the orientation angle & theta; = 45 degrees. Microstructural characterisation of the LAM 316L stainless steels was also examined by means of optical microscopy and scanning electron microscope (SEM). The microstructure analyses observe an obvious layered structure perpendicular to the building direction and some columnar crystals perpendicular to the layer plane crossing the boundary, which might explain the reasons causing the high anisotropy of the macroscopic mechanical properties of LAM steels.
