The effect of laser remelting in the formation of tunable nanoporous Mn structures on mild steel substrates

Nanoporous manganese was fabricated by a three-step process involving high power laser cladding of a homogeneous Cu₄₀Mn₆₀ alloy coatings onto a mild steel substrate, laser remelting for tuning the grain size and the composition homogeneity followed by selectively electrochemical de-alloying for removal of Cu element and formation of nanoporous Mn. The microstructure and homogeneity of the precursor Cu₄₀Mn₆₀ alloys have a significant influence on the evolution of nanopores during selectively electrochemical de-alloying. Laser remelting can significantly refine the microstructure. The second dendrite arm spacing decreases with increasing of laser remelting scanning speed. A SDAS of 1.17 μm was obtained at the laser scanning speed of 133 mm/s. When the remelting scanning speed reaches 100 mm/s, a nanoporous structure with average pore size less than 100 nm was achieved under optimized dealloying electrode current density about 2 mA/cm². Nanoporous Mn with nanopore sizes ranging from 80 to 130 nm was fabricated by this method. Surface-enhanced Raman scattering characteristics of the nanoporous materials have been investigated. It is found that smaller nanoporosity leads to significant improvements in surface-enhanced Raman scattering.