IRREVERSIBLE THERMAL EXPANSION OF REPLICATED ALUMINIUM FOAM
Keywords:aluminium, replicated foam, alumina film, micro-cracks, contraction, thermal expansion
Irreversible thermal expansion of large items made of the replicated aluminium foam was detected during the extraction of soluble filler from Al-NaCl composite. Sources of the phenomenon were investigated The expansion discovered was caused by incomplete contraction of the porous metal due to the oxidation of its internal porous surface in air and water mediums during thermal cycling. Significant influence of oxide film defects on the expansion process was shown. The information about irreversible thermal expansion dependence on temperature of the extraction process and metal foam pore size was collected. Measurements of expansion dynamics showed its finite character. It was also noted that the expansion is limited by the thermal expansion coefficient of an alloy used. Finally, correction coefficients were obtained that, being applied to nominal sizes of a porous item, compensates the expansion.