Solid State Foaming of Nickel, Monel, and Copper by the Reduction and Expansion of NiO and CuO Dispersions

Abstract

Nickel and its alloys are useful in a range of applications, and nickel foams have increased in popularity for functional applications, such as electrodes. Despite their versatility and interest for burgeoning technologies, there is only one well-developed method for producing porous nickel commercially. This work introduces a simple method for creating porosity in nickel and Monel (70% Ni, 30% Cu) that results in sub-micron to micron-scale pores and grains. This is accomplished by creating oxide dispersions in the metallic matrix and then reducing those oxides at elevated temperature to form pores. It is found that nickel and Monel reach maximum porosity at 800 °C with Monel reaching a higher overall porosity (33% vs. 25% for Ni), whereas Cu exhibited 40% porosity under the same conditions. Varied matrix and oxide pairings are examined microstructurally, and the effects of matrix strength, oxide chemistry, and other factors are considered to determine factors in pore development. Uniquely, this method produces pores within individual metallic particles, so this porosity can be added to other powder methods of solid state foaming to enhance the performance in functional applications.