Investigation of the Al–Ti–Pd alloy system at 930 and 1100 °C

Phase equilibria in the ternary Al–Ti–Pd system have been investigated in the range of the Pd content below 50 at.%. Partial 930 and 1100 °C isothermal sections are constructed.High-temperature bcc solid solution based on β-Ti (A2) widely extends into ternary compositions. With increasing Pd concentration it obeys the CsCl-type ordering (B2) and this high-temperature ordered solid solution links with that between congruent TiPd and AlPd. The Al-rich end of the low-temperature α-Ti region extends up to 6 at.% Pd. The Al–Ti γ-phase and η-phase extend up to 5 at.% Pd. Other binary Al–Ti and Pd–Ti intermetallics dissolve below 3 at.% of the third element.Three ternary compounds τ1, τ2 and τ3 reported earlier were confirmed. The τ1-phase (Pm3¯m, a = 0.39620 nm) exists in a compositional range between Al60Ti27Pd13 and Al70Ti23Pd7 at 1100 °C and between Al61Ti25Pd14 and Al69Ti24Pd7 at 930 °C. The τ2-phase (Fm3¯m, a = 1.22589 nm) exists between Al53Ti23Pd24 and Al54Ti21Pd25. The τ3-phase exists in a range between Al42Ti33Pd25 and Al49Ti32Pd19 at 1100 °C and between Al40.5Ti33.5Pd26 and Al48Ti33Pd19 at 930 °C. Apart from the basic structure (P63/mmc, a = 0.51383, c = 0.82438 nm) also a superstructure of the of the Nb(Ir,Al)2-type (P63/mcm, a = 0.89098(11) nm, c = 0.82011(7) nm) was confirmed at the Pd-rich end of this compositional region. According to our preliminary results τ1 melts incongruently at about 1420 °C while τ3 melts congruently at 1295 °C. The τ2-phase is formed in a solid-state reaction between 1050 and 1100 °C.

Research highlights▶ The Al–Ti–Pd phase diagram is studied for the first time at 930–1100 °C.