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Preparation of Al-Ti-Alloy closed-cell metal foams via foaming of powder compacts
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The foaming behavior of 5 wt% 30-45, 45-56, 56-90, 90-106, 106-160 and 160-200 .m size spherical Ti6Al4V particle-added Al powder compacts were investigated for determining the effects of wetted particles on the expansion and stability of Al powder compacts. In order to determine the effect of particle-addition on the foaming behavior, Al compacts without particle addition prepared with same method were also foamed. Foaming experiments were performed using an in-situ foam expansion measuring system at 700-730C. Small compression test samples were further core drilled from Ti6Al4V-Al foam samples and tested at quasi-static strain rates.Al compacts showed the characteristic expansion-time curve, composing of 4 distinct regions. The expansion of 5 wt% Ti6Al4V-added compacts was found to be relatively low at small size particle additions, but increased with increasing particle size.Measurements of foam expansions of 30-45 .m size Ti6Al4V-added compacts with various weight percentages of particles showed that when the wt% of particles is lower than 2 wt%, the expansion behavior of the compacts became very similar to that of pure Al. Microscopic studies have further shown that Ti6Al4V addition reduced the drainage as compared with pure Al compacts. In foaming of Ti6Al4V-Al compacts, the liquid Al reacted with Ti6Al4V particles and formed TiAl3 particles. In relatively small size particle-added foams, TiAl3 particles dispersed through cell walls and cell edges, but at increased particle size, these particles were found next to the Ti6Al4V particles. The reduced drainage and lower foam expansions in the foaming of Ti6Al4V-added compacts were discussed based on the foam stabilization models in the literature. The reduced foamability of the compacts in small particle size Ti6Al4V addition was attributed to relatively high viscosities, due to higher cumulative surface area of the particles and higher rate of reaction between liquid Al and Ti6Al4V. The lower compression strength measured in Ti6Al4V-added foams was attributed to small specimen sizes, which could not show the mechanical properties of the bulk material.