Micro selective laser melting of SS316L: Single Tracks, Defects, microstructures and Thermal/Mechanical properties

With the rapid development of physical science, medical, automotive, biotechnology, energy, communication and optical fields, the demand for micro manufacturing technology is increasing. Micro selective laser melting (MSLM) is advantageous in forming precision and micro manufacturing parts because of its small spot diameter, fine powder and small layer thickness. In this paper, the surface morphology and geometric characteristics of the single tracks were studied and analyzed. The optimization of process parameters by orthogonal tests on the density, surface roughness, microstructure, microhardness and tensile strength were studied and analyzed. Besides, the effect of heat treatment on the organization of the alloy was studied, and tensile experiment and fracture morphology observations were carried out. It is shown that the laser power and scanning speed have a significant effect on the continuity of single tracks forming, and the width of the molten pool is (55 ± 5)μm. A process windows for "Scanning speed-Hatch spacing" was determined, which was divided into four zones: discontinuous, continuous but unstable, continuous stable, excessive melting and unstable. The orthogonal experiment was used to obtain the optimal process parameters. The density of the part was 99.79 ± 0.1%, the surface roughness Ra of the X-Y plane was 2.53 ± 0.3μm, and the Vickers hardness was 209 ± 2.4 HV. After heat treatment, residual stress relief and dissolution of segregation compounds resulted in grain refinement, uniform organization and better mechanical properties. After SRAT + ST, the tensile strength was 499 ± 4.3 MPa, the elongation was 50 ± 1.88%, and the hardness was176 ± 2.0 HV. The tensile fracture dimples are uniformly distributed in size and show equiaxial dimples morphology.