Abstract
Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve.
Highlights
Porous metals with open, connected cells are ideally suited to applications involving heat exchange with a fluid which permeates the porous structure
Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting
Penetration of molten Al occurred into beads of all sizes
Summary
Porous metals with open, connected cells are ideally suited to applications involving heat exchange with a fluid which permeates the porous structure. These structures with small pores are significantly stronger than their counterparts with large (400 μm) pores [2,3] This difference in strength could not be completely accounted for by the change in topology [2] and has been attributed to the formation of a hard, 100 nm thick, load-bearing oxide layer on the cell surfaces during the salt leaching process. This oxide layer affects plastic flow in the cell walls, the effect being marked for pore sizes below roughly 100 μm [5]. As an extension to this previous work, this paper presents the structure and compressive mechanical properties for porous Al made by the infiltration of preforms made from porous, spherical NaCl beads with sizes ranging from 0.5 to 3.1 mm in diameter
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