A study of the Al-rich part of the Al-Ni-Pt alloy system

Article abstract of DOI:10.1016/j.jallcom.2011.10.076

The Al-Ni-Pt phase diagram was studied in the compositional region from 50 to 100 at.% Al. Isothermal sections were determined at 1000, 900 and 790 °C. At 1000 °C the Al₂Pt phase was found to extend up to ～Al₅₃Ni₂₃Pt₂₄ composition, separating the (Al₃Pt₂) and (Al₃Ni₂) phase fields. Two ternary structures were revealed. The one forming between ～Al ₇₅Ni₃Pt₂₂ and Al₇₅Ni ₉Pt₁₆ is rhombohedral isostructural to Al ₂₈Ir₉ and the other forming between ～Al ₇₃Ni₈Pt₁₉ and Al_72.5Ni ₁₈Pt_9.5 has an orthorhombic ε₆ structure typical of Al-Pd and Al-Rh.

Full text of DOI:10.1016/j.jallcom.2011.10.076

Journal of Alloys and Compounds 514 (2012) 60–63
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Journal of Alloys and Compounds
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A study of the Al-rich part of the Al–Ni–Pt alloy system
B. Grushkoa,∗, D. Kapushb, L. Meshic
a PGI-5, Forschungszentrum Jülich, D-52425 Jülich, Germany
b I.N. Frantsevich Institute for Problems of Materials Science, 03680 Kyiv 142, Ukraine
c Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 August 2011
Received in revised form 20 October 2011
Accepted 21 October 2011
Available online 7 November 2011
The Al–Ni–Pt phase diagram was studied in the compositional region from 50 to 100 at.% Al. Isothermal
sections were determined at 1000, 900 and 790 ◦C. At 1000 ◦C the Al2Pt phase was found to extend up
to ∼Al53Ni23Pt24 composition, separating the (Al3Pt2) and (Al3Ni2) phase fields. Two ternary structures
were revealed. The one forming between ∼Al75Ni3Pt22 and Al75Ni9Pt16 is rhombohedral isostructural to
Al28Ir9 and the other forming between ∼Al73Ni8Pt19 and Al72.5Ni18Pt9.5 has an orthorhombic ␧6 structure
typical of Al–Pd and Al–Rh.
Keywords:
Transition metal alloys and compounds
Phase diagrams
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
solidified ingots inserted into the Al2O3 crucibles were thermally annealed under
vacuum at 790, 900 and 1000 ◦C up to 235 h and subsequently water quenched. The
annealed samples were studied by powder X-ray diffraction (XRD, Cu K␣1 radiation
For reasons of practical interest, the Al–Ni–Pt phase diagram
has mainly been studied in its low-Al part and at quite elevated
temperatures (see Ref. [1–3]). The first published version of the
Al–Ni–Pt ternary diagram in Ref. [1] included the 1060 ◦C isother-
mal section in the whole compositional region. No ternary phases
were reported in this work. Several quite speculative details of this
study were not confirmed in more recent work. For example, in
Refs. [2,3] a wide extension of Al2Pt was observed towards lower Al,
which cuts the continuity between isostructural Al3Ni2 and Al3Pt2
suggested in Ref. [1]. In Ref. [4] also a ternary phase, isostructural
to Al28Ir9, was recently revealed somewhat below 1100 ◦C at the
Al74Ni7.2Pt18.8 composition.
In the present contribution we report a study of the Al-rich part
of the Al–Ni–Pt alloy system at 790 to 1000 ◦C. The experimental
data for the boundary binary system Al–Ni are used from Ref. [5]
and for Al–Pt mainly from Ref. [6]. The highest-Al Al–Pt phase, des-
ignated Al21Pt5 in Ref. [6], was reinvestigated in Ref. [7] where its
structure was determined and the more appropriate formula Al4Pt
was asserted.
was used), and scanning electron microscopy (SEM). The local phase compositions
were determined in SEM by energy-dispersive X-ray analysis (EDX) on polished
unetched cross sections. TEM examinations of selected samples were carried out on
powdered materials dispersed on grids with carbon film.
3. Results and discussion
Below the Al2Pt–Al3Ni2 line the constitution of the Al–Ni–Pt
alloy system was not visibly different at 1000 ◦C from that at 1100 ◦C
(see Fig. 1; for the comparison the relevant part of the diagram at
1100 ◦C is redrawn from Ref. [3] in Fig. 1a). The Al2Pt phase was
found to extend up to at least the Al53Ni23Pt24 composition, sep-
arating the (Al3Pt2) and (Al3Ni2) phase fields. Below 1000 ◦C this
compositional region was not studied.
Two ternary structures were revealed at higher Al concentra-
tions. Their powder XRD patterns are shown in Fig. 2 together with
the patterns of the neighboring binary phases, and their crystal-
lographic data are included in Table 1. Both ternaries are formed
between 1000 and 1100 ◦C. One is designated ␹ due to its simi-
larity to the Al–Ir ␹-phase (the latter is described in Ref. [8] and
references therein). The detailed diffraction data of the Al–Ni–Pt
␹-phase are provided in Ref. [4]. The powder X-ray diffraction pat-
tern of the other ternary phase (Fig. 2b) recalls that of the Al–Ni–Ir
␧-phase reported in Ref. [9]. Electron diffraction examinations (see
2. Experimental
Due to the high price of Pt the alloys were mainly produced from samples
previously studied in Ref. [3]. These samples were mixed in specific proportions
between them and with Al or Al–Ni alloys. Initial alloys of 2–5 g were produced
by levitation induction melting in a water-cooled copper crucible under a pure Ar
atmosphere. The purity of Al was 99.999%, of Ni 99.98%, and of Pt 99.9%. Parts of the
Fig. 3a and b) revealed the ␧ structure, also forming in Al–Rh and
6
Al–Pd and dissolving a significant percentage of numerous transi-
tion elements (see Ref. [10] and references therein). The presence
of the ternary ␹-phase was also verified by electron diffraction, see
Fig. 3c. The latter was found to be formed in a compositional region
∗
Corresponding author. Tel.: +49 2461 612399; fax: +49 2461 616444.
E-mail address: b.grushko@fz-juelich.de (B. Grushko).
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.10.076

B. Grushko et al. / Journal of Alloys and Compounds 514 (2012) 60–63
61
Al
Al
a)
c)
10
10
L
90
90
20
20
χ
L
80
80
Al21Pt8
ε
30
30
70
70
(Al21Pt8)
?
Al3Ni2
40
Al3Pt2
(Al3Ni2)
60
(Al2Pt)
10
at.% Ni
30
20
β
(AlPt)10
at.% Ni
d)
20
30
Al
40
Al
b)
10
10
90
90
20
χ
Al4Pt 20
L
80
80
χ
Al21Pt8
ε
Al3Ni
ε
30
30
70
70
(Al21Pt8)
Al3Ni2
40
Al3Pt2
(Al3Ni2)
?
(Al2Pt)
60
10
at.% Ni
30
20
β
(AlPt) 10
at.% Ni
20
30
40
Fig. 1. Partial isothermal sections of Al–Ni–Pt at: (a) 1100 ◦C redrawn from Ref. [3], (b) 1000 ◦C, (c) 900 ◦C and (d) 790 ◦C. L is the liquid. The compositions of the studied
samples are shown by spots. The compositions of the phases determined by SEM/EDX are shown by squares. Provisional tie-lines are shown by broken lines. The ranges
where the equilibria were not clarified are marked by (?).
Table 1
Crystallographic data of the phases mentioned in the text and figures.
Phase
Space group
Lattice parameters
Composition, at.%
Reference
a [nm]
b [nm]
c [nm]
Al
Ni
Pt
Al4Pt
Al21Pt8
P3c1
I41/a
1.3077
1.297
1.2911 (6)
0.5920
0.59411 (5)
0.4208
0.4864
0.48202 (11)
0.6598
0.4028
0.4083 (6)
0.2887
–
–
–
–
–
–
–
–
0.96342
1.065
1.0615 (8)
–
80
72.4
71
66.7
53
60
50
51
75
60
0
0
4
0
23
0
20
27.6
25
33.3
24
40
50
39
0
[7]
[13]
This work
[13]
This work
[13]
[13]
This work
[5]
[5]
This work
[5]
¯
Fm3m
Al2Pt
–
¯
Al3Pt2
AlPt
P3m1
0.5172
–
–
0.4802
0.4891
0.4984 (10)
–
P213
0
10
25
40
30
50
Al3Ni
Al3Ni2
Pnma
0.7351
–
–
–
¯
P3m1
0
10
0
60
50
¯
AlNi (␤)
Pm3m
␹
␧
P31c
Pna21 orPnma
1.20953
–
2.6932
74.0
73
7.2
10.5
18.8
16.5
[4]
This work
2.34a
1.65a
1.24a
a
Electron diffraction data.

62
B. Grushko et al. / Journal of Alloys and Compounds 514 (2012) 60–63
investigation of the three-phase samples, and those of
a)
b)
␹–(Al21Pt8)–L, ␹–(Al21Pt8)–␧, ␹–␧–L and (Al21Pt8)–␧–(Al3Ni2)
were established from the existence of the corresponding
two-phase equilibria (see Fig. 1c).
With the temperature decrease two additional binary phases
are involve in equilibria. The Al3Ni phase is formed below 854 ◦C
[5] and Al4Pt below 806 ◦C [6]. Investigation of Al-rich alloys at
790 ◦C revealed the equilibria presented in Fig. 1d. The extension
of the Al4Pt phase into the ternary compositional range was not
determined at this temperature, but in as-cast alloys this phase
was found to contain up to 6.5 at.% Ni. Therefore it is plausible that
at 790 ◦C its compositional region is sufficiently wide to prevent the
L–(Al21Pt8) equilibrium at lower Ni concentration, while at higher
Ni concentration this is not possible due to the extension of the ␹-
phase. Therefore the ␹–(Al4Pt)–(Al21Pt8) equilibrium is suggested.
It is worth noting that a structure associated with the ␹-phase
was earlier observed by electron diffraction in Ref. [11] in a rapidly
solidified Al5Pt alloy. This observation was confirmed in Ref. [12]
where the same electron diffraction patterns were obtained from
materials formed by the annealing of subsequent Al and Pt layers. In
both Refs. [11,12], these diffraction patterns were associated with a
metastable phase and not included in the equilibrium Al–Pt phase
diagram. Together with these observations our experiments point
to the stabilization of a metastable Al–Pt ␹-phase by Ni. Extrap-
olation of the region of the ternary ␹-phase towards the Al–Pt
terminal results in a composition close to Al3Pt, i.e. quite similar
to the composition of the Al–Ir ␹-phase determined in Ref. [8]. This
composition rather than Al5Pt reported in Ref. [11] is correct.1
In contrast to the ␹-phase, no Al–Pt metastable phase was asso-
ciated in the literature with any of the ␧-structures. The description
c)
d)
20
30
40
2θ, º
50
Fig. 2. Powder X-ray diffraction patterns (Cu K␣1-rad.) of the Al–Ni–Pt: (a) ␹-phase,
(b) ␧-phase, compared to those of (c) Al21Pt8 (calculated from the data of 58137-
ICSD) and (d) Al4Pt (calculated from the data of Ref. [7]).
Fig. 3. Precession electron diffraction patterns taken from the ␧-phase along: (a) the [0 1 0] and (b) [1 0 0] orientations, and from the ␹-phase along the [0 0 1] orientation.
The patterns were obtained with a precession angle of ∼2◦ (34.9 mrad). Reflections with high dhkl values, which appear close to the transmitted beam, are of a dynamical
nature, thus some extra reflections are visible.
maximally extended between Al75Ni4Pt21 and Al75Ni6Pt19. The
compositions of the ␧-phase were found to extend from Al73Ni8Pt19
of the second metastable structure observed in the Al–Pt system
in Ref. [12] is not sufficiently detailed but probably does not con-
to Al72.5Ni14Pt13.5
.
firm an ␧-phase formation. Also a metastable phase with unclear
structure, reported in Ref. [13] to be observed in splat-cooled
samples and designated Al3Pt(m), could rather be the ␹-phase.
However, the existence of a metastable Al–Pt ␧-phase would not
be very surprising, since, as already mentioned above, such struc-
tures are formed in Al–Pd. Both Pd and Pt belong to the same
Above 60 at.% Al the ternary equilibria ␧–(Al2Pt)–(Al21Pt8),
␧–(Al2Pt)–(Al3Ni2) and ␧–(Al3Ni2)–L were determined from
the investigation of the three-phase samples, and those of
␹–(Al21Pt8)–L, ␹–(Al21Pt8)–␧ and ␹–␧–L were established from the
existence of the corresponding two-phase equilibria (see Fig. 1b).
At 900 ◦C the compositional regions of the ternary phases are
somewhat wider than at 1000 ◦C (Fig. 1c). The ␹-phase was found
in a compositional region maximally extended from Al75Ni3Pt22 to
Al75Ni9Pt16, and the ␧-phase from Al73Ni10Pt17 to Al72.5Ni18Pt9.5
.
1
Actually, Al5Pt was mentioned to be an alloy composition, and the alloy also
Instead of the ␧–(Al2Pt) equilibrium the (Al21Pt8)–(Al3Ni2) equi-
librium was observed. The ternary equilibria ␧–(Al3Ni2)–L
and (Al21Pt8)–(Al2Pt)–(Al3Ni2) were determined from the
contained other phases. Therefore, the metastability of this binary structure is not
obvious from the experiments presented in Ref. [11], and the same conclusion con-
cerning the Al–Ir ␹-phase was incorrect (see Ref. [8] for details).

B. Grushko et al. / Journal of Alloys and Compounds 514 (2012) 60–63
63
isothermal sections were constructed. At 1000 ◦C the Al2Pt phase
extends up to ∼Al53Ni23Pt24 composition, separating the (Al3Pt2)
and (Al3Ni2) phase fields. The phase equilibria involve two ternary
phases ␹ and ␧, maximally extended between ∼Al75Ni3Pt22 and
Al75Ni9Pt16 and between ∼Al73Ni8Pt19 and Al72.5Ni18Pt9.5, respec-
tively.
χ
30
70
ε
Acknowledgements
at.% Ni
30
10
20
The authors thank B. Jülich and A. Besmehn for technical
contributions and A. Kovács for helpful discussion. D.K. thanks
Forschungszentrum Jülich for hospitality.
Fig. 4. Overall compositions of the ␹ and ␧ phases in Al–Ni–Ir (broken lines) and
Al–Ni–Pt (filled).
column of the periodic table and contain isostructural phases at
Al4TM and Al21TM8 (TM = Pd or Pt). In Al–Pd the high-temperature
␧-phases are formed at compositions including that of the low-
temperature Al21Pd8 phase (see Ref. [14]). This would also be
a composition expected for a metastable Al–Pt ␧-phase. It has
a slightly lower Al concentration than the ␹-phase, which is in
agreement with their ternary compositional regions. Therefore,
the formation of the ternary ␧-phase could also be an exam-
ple of the stabilization of a binary metastable phase by Ni. The
stabilization of a metastable ␧-phase was already suggested in
Al–Ni–Ir, where it is stable in a compositional region extending
from Al73Ni4Ir23 to Al72Ni17.5Ir10.5 (see Ref. [9]). The compositional
regions of the ␹ and ␧ phases in Al–Ni–Ir and Al–Ni–Pt are compared
in Fig. 4.
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4. Conclusions
We report a study of the Al–Ni–Pt alloy system in a compo-
sitional range of above 50 at.% Al. Partial 1000, 900 and 790 ◦C