Enhanced mechanical strength and corrosion resistance of MWCNT-reinforced SS 316L nanocomposites via spark plasma sintering

• Synergistic effects of ball milling and spark plasma sintering on the properties of 316 L-based nanocomposites. • Significant reduction in steel powder particle size and more uniform distribution of nanotubes due to two-step ball milling. • Increased hardness, compressive strength, and reduced friction coefficient due to harmonic and multiphase structure. • Transition from pitting corrosion to surface corrosion and formation of a nanostructured network of corrosion product. In this study, 316 L stainless steel/MWCNT nanocomposites containing 0.5, 1, 1.5, and 2 wt.% CNTs were fabricated by spark plasma sintering. The effects of CNTs on the microstructure, mechanical properties, corrosion resistance, and wear behavior were systematically examined. SS 316 L powder was milled for 10 h, then CNTs were mixed for 1 h before consolidation of the nanocomposite powders. Powders and nanocomposites were characterized using XRD, OM, Raman, EDX, and SEM. Mechanical properties were evaluated by hardness, compression, and wear testing, while corrosion behavior was assessed by potentiodynamic polarization with Tafel analysis. Milling reduced powder size from 8 to ∼1 μm (87.5 %). The 1.5 wt.% CNT sample showed the lowest porosity (∼58 % reduction), and achieved the highest hardness (539.7 HV) and compressive strength (1174 MPa) due to grain refinement, carbide formation, and effective load transfer. Moreover, the development of a harmonic structure contributed to the simultaneous enhancement of both strength and toughness in this sample. The nanocomposite containing 2 wt.% CNTs exhibited the highest wear resistance, the lowest coefficient of friction (∼23 % reduction), and about 63 % lower weight loss and wear rate, which was attributed to the extensive presence of CNTs. A 1.5 wt.% CNT addition also yielded the highest polarization resistance (311 kΩ·cm²) and the lowest corrosion current density (1.27 μA/cm²), and a ∼91 % reduction in corrosion rates (12.66 to 1.09 µm/year). These improvements are attributed to the formation of a nanostructured oxide network and the uniform dispersion of CNTs, which act as effective barriers against chloride ingress.