573 K and 773 K isothermal sections of the phase diagram of the Pr-Ni-Ti ternary system

Article abstract of DOI:10.1016/S0925-8388(00)01215-9

The 573 K and 773 K isothermal sections of the phase diagram of the Pr-Ni-Ti ternary system were investigated by X-ray diffraction, differential thermal analysis, optical microscopy and electron microscopy techniques. The 573 K isothermal section was rest

Full text of DOI:10.1016/S0925-8388(00)01215-9

Journal of Alloys and Compounds 316 (2001) 172–174
L
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The 573 K and 773 K isothermal sections of the phase diagram of the
Pr–Ni–Ti ternary system
*
XiaPing Zhong, Zhao Yang, Jingqi Liu
Institute of Materials Science, Guangxi University, Nanning, Guangxi 530004, People’s Republic of China
Received 10 July 2000; accepted 15 August 2000
Abstract
The 573 K and 773 K isothermal sections of the phase diagram of the Pr–Ni–Ti ternary system were investigated by X-ray diffraction,
differential thermal analysis, optical microscopy and electron microscopy techniques. The 573 K isothermal section was restricted to the
Pr-rich and Ti-rich parts of the Pr–Ni–Ti ternary system. The 773 K isothermal section was restricted to the Ni-rich part of the Pr–Ni–Ti
ternary system. The (partial) 573 K isothermal section consists of 6 single-phase regions, 9 two-phase regions, and 4 three-phase regions.
The (partial) 773 K isothermal section consists of 9 single-phase regions, 15 two-phase regions and 7 three-phase regions. The maximum
solid solubilities of Ti in PrNi , PrNi , Pr Ni , PrNi , and Ni are about 2.5 at.% Ti, 1.5 at.% Ti, 1.0 at.% Ti, 2.0 at.% Ti, and 7.5 at.% Ti
2
3
2
7
5
at 773 K, respectively. The solid solubilities of the other single-phase regions were too small to observe. The existence of any ternary
compounds was not observed in the two partial ternary isothermal sections. The decomposition of NiTi was not observed in the Ni–Ti
binary system or in the Pr–Ni–Ti ternary system.
 2001 Elsevier Science B .V . All rights reserved.
Keywords: Pr–Ni–Ti phase diagram; Ternary isothermal section; Praseodymium nickel titanium
1
. Introduction
2. Experimental
The alloys of the Pr–Ni system are hydrogen-storage
The purities of praseodymium, nickel and titanium used
in this work are 99.9, 99.99 and 99.99%, respectively. The
alloys buttons were prepared in an argon atmosphere in a
vacuum arc furnace. In all, 226 samples were prepared,
each weighing 3 g.
materials. The alloys of the Ni–Ti system do not only
show a good hydrogen-storage performance, but also
possess excellent shape memory properties. The phase
diagram and the thermodynamics are an important basis
for materials research and material applications. The Pr–Ni
binary phase diagram was reported in Ref. [1]. The
The samples were kept sealed in evacuated silica tubes
during homogenization. The homogenization temperature
of the alloys were chosen on the basis of the binary phase
diagram of the Pr–Ni, Ni–Ti and Pr–Ti systems. The
samples which contained more than 50 at.% Pr were
homogenized at 723 K for 45 days. The samples which
contained between 30 and 50 at.% Pr were homogenized at
823 K for 45 days. The rest of the alloys were homogen-
ized at 1173 K for 30 days. The samples for the 773 K
existence of seven compounds was confirmed: Pr Ni,
3
Pr Ni , PrNi, PrNi , PrNi , Pr Ni and PrNi . The Ni–Ti
7
3
2
3
2
7
5
binary phase diagram was reported in Refs. [2,3]. The
existence of three compounds was confirmed: NiTi , NiTi
2
and Ni Ti. The Pr–Ti binary system phase diagram was
3
reported in Ref. [4]. The existence of any compounds was
not observed in the Pr–Ti binary system. Up to the present,
the phase diagram of the Pr–Ni–Ti ternary system has not
been reported.
2
1
isothermal section were cooled at a rate of about 10 K h
to 773 K, kept at 773 K for 7 days and quenched into an
ice–water mixture. The samples for the 573 K isothermal
2
1
section were cooled at a rate of about 10 K h to 573 K,
kept at 573 K for 7 days and quenched into an ice–water
mixture. Samples for X-ray diffraction analysis were
powdered and annealed at 773 or 573 K for 7 days in small
glass tubes in vacuum, then the samples were quenched
*
Corresponding author.
E-mail address: lmzeng@gxu.edu.cn (J. Liu).
0
925-8388/01/$ – see front matter
 2001 Elsevier Science B .V . All rights reserved.
PII: S0925-8388(00)01215-9

X. Zhong et al. / Journal of Alloys and Compounds 316 (2001) 172–174
173
into liquid nitrogen. The alloy powders or buttons were
investigated by X-ray diffraction, optical microscopy, SEM
and EDAX.
The X-ray diffraction analysis was performed with
powder samples using a Rigaku 3015 diffractometer. A
molybdenum target, a voltage of 45 kV, a current of 15 mA
and a zirconium filter were used. Metallographic analysis
were performed using optical microscopy and scanning
electron microscopy techniques.
3
. Results and discussion
3
.1. Solid solubility
The maximum solid solubility of Ti in Ni, PrNi5,
Pr Ni , PrNi , and PrNi , is about 7.5 at.% Ti, 2.0 at.% Ti,
2
7
3
2
1
.0 at.% Ti, 1.5 at.% Ti, and 2.5 at.% Ti at 773 K,
respectively. The solid solubility of the other single-phase
regions are too small to be observed.
3
.2. Stability of NiTi
In Refs. [2,3] it was concluded that NiTi decomposes
Fig. 1. 573 K isothermal section of the phase diagram of the portion of
the Pr-rich and Ti-rich of the Pr–Ni–Ti ternary system.
into NiTi2 and Ni Ti at about 903 K. However, Refs.
3
[5–7] concluded that NiTi does not decompose into NiTi2
and NiTi at 903 K. In Ref. [5] it was concluded that the
3
equiatomic parent phase NiTi is stable down to 370 K.
Under the present experimental conditions, the decomposi-
tion of the NiTi phase was not observed in the Ni–Ti
binary system nor in the Pr–Ni–Ti ternary system. There
are several opinions as to the stability of the NiTi
compound at present.
H1M, I1J, J1N, N1L, L1M, and M1D. The 7 three-
phase regions are: C1D1G, D1G1H, D1H1M, H1L1
M, H1L1N, H1I1J, and H1J1N. The maximum solid
solubilities of Ti in Ni, PrNi , Pr Ni , PrNi , and PrNi ,
are about 7.5 at.% Ti, 2.0 at.% Ti, 1.0 at.% Ti, 1.5 at.% Ti,
and 2.5 at.% Ti at 773 K, respectively. The solid solubility
5
2
7
3
2
3
.3. Isothermal sections
By comparing and analyzing the X-ray diffraction
patterns of 226 samples and by identifying the phase in
each sample, the 573 and 773 K isothermal sections of the
phase diagram of the ternary system Pr–Ni–Ti were
determined. The former was restricted to the Ni-poor part,
the latter to the Ni-rich part. Figs. 1 and 2 show the two
partial isothermal sections, respectively. The 573 K iso-
thermal section consists of 6 single-phase regions, 9 two-
phase regions and 4 three-phase regions. The 6 single-
phase regions are: A(Ti), B(Pr), C(NiTi ), D(PrNi),
2
E(Pr Ni ) and F(Pr Ni). The 9 two-phase regions are:
7
3
3
A1B, A1C, C1D, D1E, E1F, F1B, B1C, C1F, and
C1E. The 4 three-phase regions are: A1B1C, B1C1F,
C1E1F, and C1D1E. The 773 K isothermal section
consists of 9 single-phase regions, 15 two-phase regions
and 7 three-phase regions. The 9 single-phase regions are:
C, D, G(NiTi), H(Ni Ti), I(Ni), J(PrNi ), N(Pr Ni ),
3
5
2
7
L(PrNi ), and M(PrNi ). The 15 two-phase regions are:
C1D, C1G, G1D, G1H, H1D, H1I, H1J, H1N, H1L,
3
2
Fig. 2. 773 K isothermal section of the phase diagram of the Pr–Ni–Ti
ternary system (Ni-rich portion).

1
74
X. Zhong et al. / Journal of Alloys and Compounds 316 (2001) 172–174
[
[
[
2] J.L. Murray, in: T.B. Massalski, P.R. Subramanian, H. Okamoto, L.
in other single-phase regions is too small to be observed.
The existence of any ternary compounds was not observed
in the two isothermal sections.
Kacprzak (Eds.), Binary Alloy Phase Diagrams, 2nd Edition, ASM
International, Materials Park, OH, 1991, pp. 2432–2435.
3] J.L. Murray, in: T.B. Massalski, P.R. Subramanian, H. Okamoto, L.
Kacprzak (Eds.), Binary Alloy Phase Diagrams, 2nd Edition, ASM
International, Materials Park, OH, 1991, pp. 2847–2876.
4] T.B. Massalski, H. Okamoto, P.R. Subramanian, L. Kacprzak, in:
Acknowledgements
2
nd Edition, Binary Alloy Phase Diagrams, Vol. 3, ASM, Materials
Park, OH, 1990, p. 3108.
5] W. Tang, Metall. Mater. Trans. A 28A (1997) 537–544.
6] H. Liang, Z. Jin, Caphad 17 (4) (1993) 415–425.
The work was jointly supported by the National Natural
Science Foundation of China and the National Science
Foundation of Guangxi (Matching Items).
[
[
[7] C. Colinet, A. Pasturel, Physica B 192 (1993) 238–246.
References
[
1] Y.Y. Pan, P. Nash, in: T.B. Massalski, P.R. Subramanian, H.
Okamoto, L. Kacprzak (Eds.), Binary Alloy Phase Diagrams, 2nd
Edition, ASM International, Materials Park, OH, 1991, p. 2843.