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

Abstract 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 τ 1 , τ 2 and τ 3 reported earlier were confirmed. The τ 1 -phase ( P m 3 ¯ m , a  = 0.39620 nm) exists in a compositional range between Al 60 Ti 27 Pd 13 and Al 70 Ti 23 Pd 7 at 1100 °C and between Al 61 Ti 25 Pd 14 and Al 69 Ti 24 Pd 7 at 930 °C. The τ 2 -phase ( F m 3 ¯ m , a  = 1.22589 nm) exists between Al 53 Ti 23 Pd 24 and Al 54 Ti 21 Pd 25 . The τ 3 -phase exists in a range between Al 42 Ti 33 Pd 25 and Al 49 Ti 32 Pd 19 at 1100 °C and between Al 40.5 Ti 33.5 Pd 26 and Al 48 Ti 33 Pd 19 at 930 °C. Apart from the basic structure ( P 6 3 / mmc , a  = 0.51383, c  = 0.82438 nm) also a superstructure of the of the Nb(Ir,Al) 2 -type ( P 6 3 / 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 τ 1 melts incongruently at about 1420 °C while τ 3 melts congruently at 1295 °C. The τ 2 -phase is formed in a solid-state reaction between 1050 and 1100 °C.