Adjusting microstructure and improving mechanical property of additive manufacturing 316L based on process optimization

In additive manufacturing (AM), printing defects or columnar-coarse grains due to an inappropriate process parameter often damage the mechanical properties of AM metals, which significantly reduce the quality and application fields of AM parts. In this work, the overlap ratio are optimized to adjust grain morphology and improve mechanical properties of 316L stainless steel fabricated by direct energy deposition (DED). In addition, the effects of fundamental process parameters (such as laser power, scanning speed, and overlap ratio) on the molten-pool size, density, grain morphology, and mechanical properties of DED-316L are systematically studied. By optimizing process parameters (such as overlap ratio, laser power, and scanning speed), the penetrating-columnar-grains morphology is eliminated, and a full dense (>99.9%) DED-316L with finer grains is achieved, without either adjusting the chemical composition of 316L or adding any intermediate processes (such as in-situ rolling, ultrasonic treatment, laser shock peening, or cryogenic cooling). Due to the refined grains and twinning induced plasticity (TWIP) effect, strength and plasticity of DED-316L are simultaneously enhanced. To be more specific, compared to Sample (overlap ratio-4%, laser power-720 W, scanning speed-8 mm/s) without process optimization, the tensile strength and yield strength of Sample (overlap ratio-70%, laser power-720 W, scanning speed-20 mm/s) with process optimization are individually improved by 20.3% and 18.4%, while the total elongation and uniform elongation are increased by 176.7% and 173%, respectively.