Al-Ti-M (M=Mn, Cr, Ag) ternary alloys and Al-Ti-X-Y (X, Y=Mn, Cr, Ag, Fe) quaternary alloys were homogenized at 1450 K for 84.6 ks. The as-cast and homogenized specimens have been examined by laser optical microscopy, electron probe microanalysis (EPMA) and X-ray diffraction. In the quaternary system, the L12-type titanium trialuminide phases at 1450 K were confirmed in a composition region, where the composition of the L12-type phase changes continuously from the L12-type (AlX)3Ti ternary region to L12-type (AlY)3Ti ternary region, irrespective of the assorted element X and Y. After the survey of the L12-type single-phase composition in the quaternary systems, the single-phase domain was constructed in the quaternary composition diagrams. The domain exhibited a nearly ellipsoidal pipe through the L12-type (AlX)3Ti ternary region and the L12-type (AlY)3Ti ternary region for all X and Y elements considered. The amount of porosity in the homogenized quaternary alloys was larger than that in the cast alloys. The amount of porosity in the quaternary Al-Ti-Cr-Fe alloy was the smallest among the examined ternary and quaternary systems. When Ag was added into the L12-type (AlMn)3Ti or (AlCr)3Ti phases, the lattice parameter of the resultant L12-type phases increased. However, chromium addition to the L12-type (AlMn)3Ti phase did not change the lattice parameter. In the quaternary systems of Al-Ti-Mn-Fe and Al-Ti-Mn-Cr, the lattice parameter change of the L12-type phases with composition can not be explained from the atomic size effect.
