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hase Diagram Evaluations: Section II

Al-Pd-Ru (Aluminum-Palladium-Ruthenium) V. Raghavan

This ternary system was investigated by [2008Pav], who reported three isothermal sections at 1100, 1050 and 1000 °C for Al-rich alloys, which were reviewed by [2009Rag]. Recently, [2009Pav] presented an extension of this study to the temperature range of 900-790 °C.

The Pd-Ru phase diagram [Massalski2] is a simple peritectic system, with no intermediate phases.

Ternary Phases In addition to the icosahedral phase I, the occurrence of three cubic phases: C (primitive cubic, Pm3), C1 (body3) were centered cubic, Im3) and C2 (face-centered cubic, Fm reported by [2008Pav], while investigating this system in the temperature range of 1100-1000 °C. All these four phases were found by [2009Pav] to be stable down to at least 790 °C. Instead of the F40 structure reported by [2008Pav] at the Ru-rich end of the I phase, [2009Pav] found a primitive structure labeled P40 (space group Pa3) with the lattice parameter a = 4.0445 nm, which is essentially the same as that of F40. Apart from this, an additional primitive cubic phase labeled P20 was found at the Pd-rich end of the I region, with a = 2.0227 nm, which is half of the lattice parameter of P40. The phases P40 and P20 were found both at 900 and 790 °C even after prolonged annealing, but their thermodynamic stability is not firmly established [2009Pav]. Also, no compositional gap separating them from I could be detected

Binary Systems The Al-Pd phase diagram [2001Yur] depicts the following intermediate phases: PdAl4 (hexagonal, space group P6322), PdAl3 (denoted e6, orthorhombic), PdAl3 (denoted e28, orthorhombic), Pd8Al21 (Pt8Al21-type tetragonal), Pd2Al3 (denoted d, D513, Ni2Al3-type hexagonal), PdAl (B2-type cubic and two low-temperature forms: rhombohedral and B20-type cubic), Pd5Al3 (Rh5Ge3-type orthorhombic), Pd2Al (C23, Co2Si-type orthorhombic), and Pd5Al2 (Pd5Ga2-type orthorhombic). The Al-Ru phase diagram [2003Mi] depicts six intermediate phases: RuAl6 (orthorhombic, space group Cmcm), Ru4Al13 (monoclinic, space group C2/m), Ru2Al5 (orthorhombic, space group Cmcm), RuAl2 (C54, TiSi2-type orthorhombic), Ru2Al3 (Os2Al3-type tetragonal), and RuAl (B2, CsCl-type cubic).

mi

I I

nu mi

Ato

Alu

cP

nt

erc

e erc

en

cP

tR

mi

uth

Ato

en

ium

Al

m

I I I

Atomic Percent Palladium

Fig. 1 Al-Pd-Ru isothermal section at 900 °C for Al-rich alloys [2009Pav]

Journal of Phase Equilibria and Diffusion Vol. 30 No. 6 2009

631

Section II: Phase Diagram Evaluations

Alu

mi c

nt

Pe

rce

rce

Pe

nt

Ru

c mi

the

Ato

ni u m

Al

I

Ato

nu mi

I

m

I

I I

Atomic Percent Palladium

Fig. 2 Al-Pd-Ru isothermal section at 790 °C for Al-rich alloys [2009Pav]

in the experiments [2009Pav]. New complex orthorhombic structures labeled as E were found at the Ru-rich end of the e region. The results indicated that the E phases were separated by a compositional gap from the e region.

1 at.% Ru. Ru4Al13 and RuAl2 dissolve