Interface-controlled evolution of bimodal porosity in Zn-Mg alloy through vapor-phase dealloying

The present work introduces the fabrication of 3D interconnected porous structure in the Zn-Mg (Zn90Mg10) alloy system using vapor-phase dealloying (VPD) technique, carried out in a dry environment. Vacuum heating leads to selective evaporation of Zn, resulting in a connected porous network. Detailed SEM, STEM-EDS, atom probe tomography, and X-ray tomography analysis have established the presence of a bimodal pore distribution in the interconnected porous structure. Nanoscale pores are mainly formed when the Zn gets evaporated from the Mg2Zn11 phase, whereas micron-sized pores formed when the Zn phase evaporation takes place from the alloy matrix. The dual-scale porosity established here is in stark contrast to traditional pore fabrication process which only creates either nanoscale pores or micron-size pores, but not both. Kinetic study of the dealloying process of the bulk sample (mm scale) reveals that the evaporation of the Zn begins at the interface between Mg2Zn11 phase and Pure Zn phase. Therefore, the interface reaction plays a major role in the pore formation process. This study also confirms that the pore network architecture strongly depends on the dealloying temperature over holding time in the complete dealloying duration. In situ TEM experiments reveal that the Mg2Zn11 phase undergoes grain coarsening phenomena followed by solid-state phase transformation (i.e., MgZn2) prior to noticeable Zn evaporation. The resulting multiscale porous framework possesses high surface area and very high permeability. Due to these properties, Zn-Mg porous scaffolds have great potential as biodegradable implants and as functional porous electrodes.