Фазовая диаграмма системы Al-Cu
К оглавлению: Другие диаграммы (Others phase diargams)
Al-Cu (Aluminum-Copper)
J.L. Murray
The equilibrium solid phases of the Al-Cu system are (1) (Cu) and (Al), the
terminal fcc solid solutions; (Cu) is often designated a; hence the low-
temperature ordered phase based on the fcc structure is designated a2; (2) b,
the disordered bcc solid solution; b1, the ordered bcc phase, which occurs
metastably; and b0, a high-temperature phase of unknown structure; (3) phases
with structures based on g brass, g0, g1, and d; (4) the equiatomic phases, h1
and h2, and near-equiatomic phases, z1 and z2, with structures related to the
h structures; and (5) q, or Al2Cu, and metastable transition phases q› and q›
formed from supersaturated (Al) before the [q + (Al)] equilibrium is reached.
The solidus is drawn as a smooth curve joining the eutectic reaction to the
melting point of Cu; the width of the two-phase [L + (Cu)] field is consistent
with the thermodynamic properties of Cu.
The assessed phase diagram for the Al-Cu system is based primarily on review
of the work of [Hansen], [22Sto], [24Sto], [25Taz], [26Dix], [33Sto], [34His],
[36Aue], [37Dow], [53Tho], [58Vig], [71Fun], [72Lin], [76Tas], and [80San] and
was obtained using thermodynamic modeling. The intermediate composition range
of the diagram is inaccessible to thermodynamic modeling because of the
absence of thermodynamic information on the high-temperature solid phases and
the multiplicity of complex solid-state reactions. The calculated diagram
agrees well with the available experimental data in all regions within
experimental accuracy.
The bcc b solid solution is stable as a high-temperature phase at 70.6 to 82
at.% Cu; b melts congruently at 1049 с 1 C. A two-phase [(Cu) + b] field
exists between the eutectic temperature and the eutectoid reaction b = g1 + (
Cu) at 567 с 2 C.
The solubility of Al in (Cu) is 19.7 at.% Al at the eutectic temperature.
Solubility decreases below the peritectoid temperature. The a2 phase exists in
equilibrium with (Cu) and g1 below a peritectoid reaction (Cu) + g1 = a2. The
a2 phase has an ordered fcc structure. Placement of the (Cu) solvus is
uncertain. It is possible that in stable equilibrium the two-phase [a2 + (Cu)]
field may be broader than in the present diagram.
The intermetallic compounds in the Al-Cu system are very difficult to work
with, because they are hard and brittle. The structures of phases at 58 to 70
at.% Cu, g1, d, and g0, are based on the g brass structure. The g1/[g1 + (Cu)]
boundary is accurately delineated, as in the single-phase d region. The
existence of the high-temperature phase g0 of unknown structure was
demonstrated by thermal analysis, but the g0 + g1 region cannot be delineated
metallographically.
[71Fun] observed g1 and d in equilibrium in diffusion couples annealed at 500
C. [80San] compared quenched and slowly cooled structures. The quenched
alloys revealed a long-period superlattice structure, probably g2. Alloys
slowly cooled from 700 C did not reveal any new structure, but contained two
phases, (g1 + d). Thus, it appears that g2 exists as a metastable transition
phase, but not as an equilibrium phase.
The homogeneity range of z2 is 56.6 to 57.9 at.% Al. The equiatomic phases h1
and h2 are closely related structurally to the z1 and z2 phases.
q crystallizes by peritectic reaction at 590 с 1 C. The composition range is
31.9 to 32.9 at.% Cu at the eutectic temperature. The supersaturated (Al)
solid solution decomposes to form the metastable precipitates, Guinier-Preston
(GP) zones, q›, and q›. Aging treatments to prepare the desired precipitate
usually are based on hardness data as a function of composition, aging
temperature, and aging time.
There is evidence that the formation of GP zones below 130 C proceeds by a
spinodal mechanism. At room temperature, the initial decomposition is into the
solute-rich and solute-lean areas. GP zones form continuously from the
modulated microstructure.
The q› structure has been reported to contain three (001) layers that consist
of essentially pure Cu. The structure is tetragonal, not because of ordering,
but because of the constraint of coherency with the matrix. The structure is
thus identical to that of the GP zones, except for the thickness of the
precipitate. The structure of q› is a tetragonal distortion of the CaF2
structure.
Because of the sluggishness of the eutectoid reaction b = (Cu) + g1, the b
phase can be retained metastably. During quenching, metastable b alloys
undergo a martensitic transformation to a b› phase at low Al content or a g›
phase at higher Al content. The ordering reaction b = b1 precedes the
martensitic transformation. Thus, three martensitic phases actually appear: b›,
b›1 , and g›. There are two metastable three-phase equilibria: the eutectoid
reaction b = b1 + (Cu) and the peritectoid reaction b + g1 = b1. At
intermediate cooling rates (air quenching), phase separation into b + b1
occurs before the martensitic transformation.
The b = (Cu) massive transformation is initiated when a b alloy is quenched
into a single-phase (Cu) region. With increasing Al content, the massive
transformation is interrupted or ruled out by the martensite transformation,
and the maximum composition at which massive product is observed is 20.8 at.%
Al.
According to the present thermodynamic calculations, the temperature interval
between the eutectic and the minimum of the fcc/L T0 curve is only about 40 C.
From this, the formation of uniform solid solutions is far more probable than
the retention of the amorphous state.
Extended single-phase solid solutions have been reported, with a maximum
extension of about 16 or 17 at.% Cu. The decomposition of these supersaturated
solutions proceeds by the same sequence observed in solid-quenched alloys. A
new phase, Al3Cu2, isotypic with Al3Ni2 was discovered by splat quenching of
45 and 50 at.% Cu alloys [74Ram].
Metastable phases and extended solubilities also can be obtained in thin films
produced from the vapor phase. In films produced by cosputtering, [76Can]
observed fcc solid solution between 0 and 28.5 at.% Cu, an anomalous fcc
solution between 28.5 and 41.7 at.% Cu, and disordered bcc between 47.6 and 60
at.% Cu.
[77Dhe] produced the equilibrium phases g1, h2, and q by vapor evaporation, in
addition to the extended solid solutions. The (Cu) solid solution was extended
to about 78 at.% Cu, g1 was found between 65 and 70.5 at.% Cu, and h2 at 58 at.
% Cu.
22Sto: D. Stockdale, J. Inst. Met., 28, 273-286 (1922).
24Sto: D. Stockdale, J. Inst. Met., 31, 275-295 (1924).
25Taz: M. Tazaki, Kinzoku-no Kenkyu, 2, 490-495 (1925) in Japanese.
26Dix: E.H. Dix and H.H. Richardson, Trans. AIME, 73, 560-580 (1926).
33Sto: D. Stockdale, J. Inst. Met., 52, 111-118 (1933).
34His: C. Hisatsune, Mem. Coll. Eng. Kyoto Univ., 8(2), 74-91 (1934).
36Aue: H. Auer, Z. Metallkd., 28, 164-175 (1936) in German.
37Dow: A.G. Dowson, J. Inst. Met., 61, 197-204 (1937).
53Tho: D.L. Thomas and D.R.F. West, Res. Correspondence, 6(12), 61S-62S (1953).
58Vig: V.N. Vigdorovich, A.N. Krestovnikov, and M.V. Maltsev, Izv. Akad. Nauk
SSSR Otd. Tekh. Nauk, 3, 110-113 (1958) in Russian.
71Fun: Y. Funamizu and K. Watanabe, Trans. Jpn. Inst. Met., 12(3), 147-152 (
1971) in Japanese.
72Lin: G. Linden, Prakt. Metall. (Stuttgart), 9(1), 3-14 (1972) in German-
English.
74Ram: P. Ramachandrarao and M. Laridjani, J. Mater. Sci., 9, 434-437 (1974).
76Can: B. Cantor and R.W. Cahn, Acta Metall., 24, 845-852 (1976).
76Tas: M. Tassa and J.D. Hunt, J. Crystal Growth, 34, 38-48 (1976).
77Dhe: F. Dherle, Vacuum, 27(4), 321-327 (1977).
80San: M. van Sande, J. van Landuyte, M. Avalos-Borja, G. Torres, and S.
Amelinckx, Mater. Sci. Eng., 46, 167-173 (1980).
Published in Int. Met. Rev., 30(5), 1985. Complete evaluation contains 19
figures, 10 tables, and 220 references.
Special Points of the Al-Cu System