Materials Science

Sizing Up the Foam

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Science  07 Nov 2008:
Vol. 322, Issue 5903, pp. 823
DOI: 10.1126/science.322.5903.823c

Bulk metallic glasses have high plastic yield strengths, and thus have the potential for making ultrastrong foams. However, the foam will only inherit the strength of the parent glassy material if it fails by plastic yielding, rather than by brittle fracture (which is associated with the solid fracture stress) or by elastic buckling (associated with the solid modulus). Demetriou et al. look at a number of critical structural scales that influence the failure mode and find that they can make ultrastrong glassy foams from a Pd43Ni10Cu27P20 alloy with up to 92% porosity. The foams were engineered against buckling and fracture though a process that limited membrane thickness and promoted cellular periodicity. Evaluation of compressed, collapsed specimens showed both crushed cells and shear banding, indicating that although the failure was due to fracture, the initial response of the foam involved plastic deformation. Thus, the foams inherited the best properties of the parent glassy material. The compressive strength of the glassy foams rivaled those obtained for highly engineered Ti-6Al-4V or ferrous metal foams. — MSL

Phys. Rev. Lett. 101, 145702 (2008).

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