Processing And Microstructure Of Porous Cu Fabricated By Freeze-drying From CuO Powders

Porous metal has gradually become an indispensable material in various industrial fields, such as damping, de-noising and lightweighting because of their good sound absorption, being light-weight, high damping and impact. At present,most of the technology for preparing porous metal is confined to the metal as raw material, high-cost, and the preparation method is limited by the metal powder properties.In this paper, CuO powder was selected as the source for the formation of Cu via thermal vacuum decomposition due to the low vapor pressure of CuO. Porous Cu with complex shapes and directional pore channels structure was fabricated respectively by freeze-drying. The influence of the solid content on the porosity and pore structure was studied, and the formation mechanism of pore was explored. Moreover,hierarchically porous Cu with controlled pore characteristics was fabricated by pre-sintering, dissolution using NaCl as template. The influence of the NaCl content on the porosity, pore structure and properties was studied.The results showed that complex-shaped porous materials can be obtained directly using freeze drying, or machining the freeze-dried compacts, whilst the machined chips can be recycled for preparation of new slurry. The complex-shaped porous Cu showed no noticeable macroscopic defects and good shape tolerance. The CuO powder decomposition at 900 ℃ for 2 h in vacuum was composed only of Cu phase with simple process. These pores were generated from sublimation of the ice.The porosity decreased from 49.7% to 30.8% with the increase in solids content from20 to 40 vol.%. The pores became smaller and the compressive strength increased, the compressive strength was inversely proportional with the porosity.The growth direction of ice crystals can be controled by temperature gradient during the solidification process, the directional structure was replicated by freeze drying. The pore structure shrinkage during sintering. The pore channels were parallel to the temperature gradient and maintained a high degree of consistency in direction.The tunnel-pore can be controled by solid content, and decreased with the increase in solids content.The NaCl particles can be dissolved in water quickly and completely, and the pre-sintered CuO compact showed good structure integration. The porous Cu were fabricated with bimodal pore size distribution with peak locations at 12 μm and 85 μm,respectively.The large pores were formed after removal of NaCl particles, and the small pores originated from incomplete densification of Cu particles. The hierarchically porous structure was inter-connected, and the open porosity ratio of porous Cu exceeds 96.6%. The porosity increased, and the electrical conductivity, the compressive strength decreased with the increase in NaCl content. Porous Cu with high energy absorption efficiency are suitable for high impact energy absorption applications.