Fabrication of a thin open-cell Ni foam sheet with a high specific strength and moderate porosity using severe plastic deformation via differential speed rolling

Differential speed rolling was applied to an open-cell Ni foam. As the roll speed ratio increased, the cell walls were deformed into more curved shape with smaller curvatures. As the roll speed ratio increased, grain refinement in the cell walls (via continuous dynamic recrystallization) was promoted and dislocation density was increased. Porosity decreased after rolling, but it decreased less at a higher roll speed ratio. The porosity decreased from 90% to 25% after conventional rolling, while it decreased to 36% after differential speed rolling with a roll speed ratio of 3. The results herein demonstrate that differential speed rolling with a high roll speed ratio can produce a thin open-cell Ni foam sheet with a high specific strength, high hardness and moderate porosity. The mechanism of the roll speed ratio effect on the cell shape and porosity is discussed.