Microstructure and mechanical properties of ternary L12 intermetallic compound in Al-Ti-Cr system

Abstract

Sintering of elemental powders was carried out to form ternary L12 intermetallic compounds in Al-Ti-Cr alloys. The L12 phase field and equilibrium phases surrounding the L12 phase at 1423 K have been established. Besides the L12 phase, the pertinent second phase fields have been also estimated; TiAl, TiAl2, Ti2Al5, Al3Ti, Al17Cr9, AlCr2, and TiAlCr phase fields. The vertical section of the Al-25 mol%Ti-Cr alloys has been experimentally determined, and the presence of the L12+Liquid phase field in the present composition and temperature ranges was confirmed. Button ingots of some ternary L12 compounds in the Al-Ti-Cr alloys were prepared by arc-melting to investigate their microstructure (especially second phases and porosity), microhardness, and bend ductility. In general, homogenization of as arc-melted alloys substantially reduced the amount of second phases but introduced extensive porosity. Therefore, the formation of porosity is closely associated with the second phase solutionized during homogenization treatment. However, no residual porosity was observed in higher Cr alloys. The porosity after homogenization was observed when Al17Cr9 phase is formed and not when the TiAlCr or AlCr2 phase is formed. The ternary L12 compounds in the Al-Ti-Cr alloys had some bend ductility at ambient temperature, which can be increased to about 0.9% (plastic bend strain) by increasing the Cr content when porosity is reduced.