Fabrication and Compression Properties of Functionally Graded Copper Foam Made Using Friction Powder Sintering and Disso
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JMEPEG DOI: 10.1007/s11665-017-2896-z
Fabrication and Compression Properties of Functionally Graded Copper Foam Made Using Friction Powder Sintering and Dissolution Yoshihiko Hangai, Kousuke Zushida, Hidetoshi Fujii, Osamu Kuwazuru, and Nobuhiro Yoshikawa (Submitted August 2, 2016; in revised form July 20, 2017) 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 Vf = 80% (high porosity) and Vf = 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 Vf = 80% layer first deformed while the Vf = 60% layer hardly deformed at the beginning of the compression. Thereafter, the Vf = 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 Vf = 80% and Vf = 60%, respectively. Moreover, Cu foams consisting of simply stacked uniform Cu foams with Vf = 80% and Vf = 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 Vf = 80% and Vf = 60% layers. Keywords
cellular materials, functionally gradient materials, powder metallurgy, sintering
1. Introduction Functionally graded (FG) metal foams have properties that vary with the position and are expected to be lightweight and possess superior properties to ordinary metallic foams. Several processing routes for fabricating FG metallic foams have been proposed, such as the casting space holder process (Ref 1, 2), the powder metallurgy space holder process (Ref 3), the precursor foaming process (Ref 4-10) and the metal melt direct foaming process (Ref 11). In these processes, the properties variation is adjusted via the position-dependent pore structures (pore size, pore morphology and porosity) (Ref 1-8, 11) and the alloy composition (Ref 9, 10). It is expected that FG metallic foams will have controlled compression deformation behavior with the desired plateau stresses corresponding to the compression properties of the metallic foams by controlling the pore structure and al
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