Combustion Foaming of Porous (Al, Fe)₃Ti with L1₂ Ordered Structure

抄録

The combustion foaming process enables the fabrication of closed-cell porous intermetallics by utilizing the combustion reactions generating a large amount of heat. A closed-cell porous Al₃Ti (D0₂₂ crystal structure) fabricated by the combustion foaming process has a lightweight, high stiffness, high melting temperature, and good oxidation resistance but exhibits brittleness due to the poor deformability of Al₃Ti. It is known that the addition of third elements (X = Cr, Mn, Fe, etc.) changes the crystal structures from D0₂₂ to L1₂, resulting in an improvement in the deformability in the case of dense materials. In the present study, an attempt was made to fabricate the closed-cell porous (Al, Fe)₃Ti with an L1₂-ordered crystal structure through the combustion foaming. The effect of the amount of the exothermic agent, which was added to control the reaction heat of combustion foaming, on the porosity, pore morphology, microstructure, and constituent phases was investigated. The closed-cell porous L1₂-(Al, Fe)₃Ti without any intermediate phases was successfully fabricated when the exothermic agent was added over 5 vol%. The porosity reached the maximum at approximately 80% when the exothermic agent of 10 vol% was added. The TiB₂ particles, which were formed by the reactions of the exothermic agent, were aggregated in the porous sample with the exothermic agent of 5 vol% but uniformly dispersed in the porous samples foamed with the exothermic agent over 10 vol%. Based on the results above and the temperature measurements during the combustion foaming, it is important for fabricating highly porous L1₂-(Al, Fe)₃Ti with the uniform microstructure to control the maximum temperature just above the liquidus temperature of (Al, Fe)₃Ti. This study provides new insights into the hierarchical control of porous materials with the desired pore structures and cell wall materials.