Fabrication and Compression Properties of Functionally Graded Copper Foam Made Using Friction Powder Sintering and Dissolution

Functionally graded (FG) metal foams have properties that vary with the position, giving them controlled compression deformation behavior with the desired plateau stresses. In this contribution, bilayer FG Cu foams consisting of a high-porosity layer and a low-porosity layer were fabricated and their compression properties were demonstrated. A friction powder sintering process based on the sintering and dissolution process was employed to fabricate the FG Cu foams. X-ray computed tomography observations revealed that the porosity markedly changed around the boundary between the layers of the FG Cu foam with NaCl volume fractions of V (f) = 80% (high porosity) and V (f) = 60% (low porosity), and the two layers exhibited almost constant porosities and were bonded seamlessly. From compression tests on the fabricated FG Cu foams, it was found that the V (f) = 80% layer first deformed while the V (f) = 60% layer hardly deformed at the beginning of the compression. Thereafter, the V (f) = 60% layer started to deform. From the compression stress-strain curves, the FG Cu foams exhibited two plateau regions with low and high plateau stresses corresponding to the deformation behavior. The first plateau stress and second plateau stress obtained from the FG Cu foams exhibited similar values to those obtained from uniform Cu foams with V (f) = 80% and V (f) = 60%, respectively. Moreover, Cu foams consisting of simply stacked uniform Cu foams with V (f) = 80% and V (f) = 60% without bonding exhibited almost the same deformation behavior and compression properties except for slightly larger dispersion than that in the FG Cu foams, which is considered to be due to the lack of bonding and the discontinuity between the pores at the boundary between the V (f) = 80% and V (f) = 60% layers.