Peculiarities of the Microstructure and Properties of Parts Produced by the Direct Laser Deposition of 316L Steel Powder

Abstract

The direct laser deposition of metal powders is one additive method of producing functional materials. It consists of the melting of metallic powders by a laser beam in inert gas. The main process parameters are the laser-beam power, laser-beam speed and scanning trajectory, and powder consumption. Each parameter is selected depending on the alloy type, which in totality affects the structure and defect formation in products. In this study, experimental rectangular samples of 316L austenitic steel are fabricated by the direct laser deposition of the powder. The microstructure and fractures of samples are investigated using scanning electron microscopy in order to determine the structural features and reveal the defects (pores, holes, crystallization cracks, and oxide inclusions). Uniaxial tension tests and hardness tests are performed. The analysis of the influence of the laser beam scanning trajectory on the microstructure and properties of samples during melting is performed. It is found that a dispersed structure with an average crystallite size of 1.3–1.9 μm is formed at a laser power of 250 W and scanning rate of 16 mm/s, which results in a high level of mechanical properties of experimental samples. It is shown that, when using the lengthwise laser-beam trajectory (along the largest sample size), the tensile strength reaches 730 MPa with a relative elongation of 25%, which exceeds the level of mechanical properties of 316L steel by 110 MPa.