Comparison of morphology and compressive deformation behavior of copper foams manufactured via freeze-casting and space-holder methods

Abstract

Copper (Cu) foams with high porosity of about 63–78% were processed by the freeze-casting (FC) and space-holder (SH) methods. The FC and SH techniques yielded lamellar and polygonal pore structures, respectively, with similar porosities. The deformation behaviors of the two different types of Cu foams were compared using uniaxial compression and a simultaneous acoustic emission (AE) and video recording analysis. It was found that the compressive yield strength values for the FC-Cu and SH-Cu foams were significantly different, which were 19–29 MPa and 1.2–2.3 MPa, respectively. Furthermore, the energy absorbed during compression up to the strain of 50% was obtained as ∼12.3 MJ m−3 and ∼2.7 MJ m−3 for the FC-Cu and SH-Cu foams, respectively, resulting in approximately 4.6 times higher energy absorption capability for the FC-Cu foam. The deformation processes occurring during compression in the two Cu foams were studied by the AE and image analysis. The video and the evaluated AE parameters (e.g., the AE voltage, the cumulative number of events, and the cumulative energy) revealed that, in the case of the FC foam, the localized fracture of the struts within a well-defined single deformation band took place, which gave rise to pronounced AE signals (mostly in the plateau stage of compression). By contrast, the deformation was highly homogeneous in the case of the SH-Cu foam, and the main deformation mechanisms were gradual bending and buckling of the foam struts during compression.

Keywords

• Copper
• Foam
• Freeze-casting
• Space-holder
• Deformation
• Acoustic emission