Additive Manufacturing of AISI 316L Slab Using Friction Stir Surfacing: Impact on Microstructural, Mechanical and Corrosion Properties

The current work investigates the microstructural, mechanical, and corrosion properties of an additively manufactured slab of AISI 316L through friction stir surfacing (FSS), a solid-state process, and compared with the substrate. The additive manufacturing was performed with constant FSS parameters such as tool spindle speed of 1400 rpm, 30 mm/min transverse speed, 15 kN downward axial force, tool tilt angle of 1 degrees and plunge depth of 10 mm/min. The microstructure of the slab was comprised of fine and equiaxed grains across the deposited layers. The relatively finer grain size of the order 3-7 mu m attributed to a significantly higher yield strength of 345 MPa and tensile strength of 641 MPa, which is 6.8% and 12.45% higher than the base substrate. Microstructural studies confirmed the presence of delta ferrite. The presence of delta ferrite did not influence the mechanical properties, as the ferrite grains were smashed into a particle size of similar to 1 mu m during severe plastic deformation. The corrosion resistance of the additive slab was slightly less than the base substrate in a 3.5 wt% NaCl solution. A stable passive film was formed on the additive slab; however, the presence of the delta ferrite reduced its corrosion resistance in the aqueous media. The corroded surface of the additive slab comprised several pits, with a decrease in the size of the pits than that of the base metal.