Study on mechanical alloying and subsequent heat treatment of the Ti-Si system

Article abstract of DOI:10.1016/S0921-4526(99)01228-4

Elemental powder mixtures of Ti_xSi_100-x were mechanically alloyed by using a planetary ball mill. XRD, SEM, TEM and DTA were used to characterize their mechanical alloying process. After milling for 45 h, Ti₇₅Si₂₅, Ti_62.5Si_37.5 and Ti₅₀Si₅₀ powders were amorphized completely; however, no obvious amorphization was observed for Ti_33.3Si_66.7 and Ti₂₅Si₇₅ powders. By using Miedema model, a thermodynamics analysis was performed. Annealing the as-milled powders in vacuum at 860 °C for 1 h, the as-milled Ti_62.5Si_37.5 powders transformed into Ti₅Si₃ intermetallics, and Ti_33.3Si_66.7 transformed into TiSi₂ intermetallics completely.

Full text of DOI:10.1016/S0921-4526(99)01228-4

Physica B 279 (2000) 241}245
Study on mechanical alloying and subsequent heat treatment
of the Ti}Si system
ꢀꢁ
Junyou Yang* , Jiansheng Wu, Wei Hua
Open Lab of State Ministry of Education for High Temperature Materials and Testing, Shanghai Jiao Tong University, Shanghai 200030,
People's Republic of China
Received 7 July 1999; received in revised form 25 October 1999
Abstract
Elemental powder mixtures of Ti Si
were mechanically alloyed by using a planetary ball mill. XRD, SEM, TEM
V
ꢁꢂꢂ\V
and DTA were used to characterize their mechanical alloying process. After milling for 45 h, Ti Si , Ti
Si
and
and
ꢃꢄ ꢅꢄ
Ti Si powders were amorphized completely; however, no obvious amorphization was observed for Ti
ꢄꢂ ꢄꢂ
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
Si
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
Ti Si powders. By using Miedema model, a thermodynamics analysis was performed. Annealing the as-milled
ꢅꢄ ꢃꢄ
powders in vacuum at 8603C for 1 h, the as-milled Ti
Si
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
transformed into TiSi intermetallics completely. ( 2000 Elsevier Science B.V. All rights reserved.
powders transformed into Ti Si intermetallics, and
ꢄ
ꢈ
Ti
Si
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
ꢅ
Keywords: Mechanical alloying; Amorphization; Ti}Si system intermetallics
1. Introduction
method, mechanical alloying (MA) is widely used
to prepare amorphous, nanocrystalline and other
metastable structure powders. Up to now, much
MA research has been performed in the intermetal-
lic compound forming system such as Ti}Al [4}7],
Ni}Al [8}10], Nb}Al [11], etc. Recently, MA of
Ti}Si system has also been attached importance.
Ti}Si intermetallics, e.g., Ti Si and TiSi , at-
ꢄ
ꢈ
ꢅ
tract much research attention due to their favorable
properties such as low speci"c weight, high melting
temperature and good oxidation resistance [1,2].
Currently Ti Si is mainly prepared via powder
ꢄ
ꢈ
metallurgy method [3], by "rst obtaining stoichio-
Ohering et al. [12] reported that Ti
Si
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
metric Ti Si ingot through arc melting, powder-
elemental powder mixtures could be mechanically
alloyed into Ti Si intermetallics, while Rudlinski
ꢄ
ꢈ
ing by mechanical smashing or gas atomization
method, and then consolidating them by HIP or
other alternatives. As a novel powder processing
ꢄ
ꢈ
[13] reported that an amorphous phase was ob-
tained from MA of Ti Si elemental powder
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
mixtures. Oleszak et al. [14] proposed that
Ti Si "rst transformed it into Ti Si and
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ꢄ ꢈ
*Correspondence address. Mechano-Process Laboratory,
Department of Materials Science, University of Tokyo, Hongo
7-3-1, Bunkyo-Ku, Tokyo, Japan. Tel.: #81-3-5841-7130.
E-mail address: yang@dragon.mm.t.u-tokyo.ac.jp (J. Yang)
ꢁNow in the Department of Materials Science, University of
Tokyo.
subsequently transformed it to amorphous phase
over the course of MA. It can be seen that quite
di!erent results have been reported from the
same initial powder composition. In addition, the
phase transition of the as-mechanically alloyed
0921-4526/00/$- see front matter ( 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 2 2 8 - 4

242
J. Yang et al. / Physica B 279 (2000) 241}245
Ti}Si system products against heating is very
important to its subsequent consolidation and per-
formance. Therefore, in this paper we report our
investigation on mechanical alloying of the Ti}Si
system and its subsequent heat treatment.
2. Experiment
Elemental Ti (200 mesh, 99 wt%) and Si (200
mesh, 99 wt%) powders were blended at Ti : Si
atomic ratio of x : (1!x) for x"0.750, 0.625,
0.500, 0.333 and 0.250. They were mechanically
alloyed in a QM-4H planetary ball mill at a
rotating speed of 200 rpm in argon atmosphere.
The charge had a ball-to-powder ratio of 14 : 1.
Stainless-steel balls and a tool steel vial were
used. Over the course of milling, sample
powders were extracted from the vial for structure
analysis.
X-ray di!raction was performed with a Rigaku
D-MAX III di!ractometer by using Cu K radi-
a
ation. Powder morphology was observed by using
a Philips XL-30 scanning electron microscopy
(SEM). Philips CM 12 instrument operating at
120 kV was used for TEM observation and ana-
lysis. Thermal analysis of powders was performed
in a Dupont TA DSC2910 Modulated DSC at a
heating rate of 303C/min. Heat treatment of the
as-milled powders were performed in vacuum
\ꢅ
(1.5;10 Torr) at 8603C 1 h.
Fig. 1. XRD patterns of Ti
times.
Si
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
powders at di!erent milling
3. Results and discussion
amorphous phase. No intermetallics peak is ob-
served in the whole process of mechanical alloying.
TEM micrograph (Fig. 2) conforms this result,
showing only a di!usive di!racting rim in the cor-
responding electronic di!raction pattern which is
an amorphous structure di!racting character.
Fig. 1 shows the X-ray di!raction patterns of
Ti
Si
at di!erent milling times. It can be seen
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
that the peaks of Ti and Si widen and weaken with
increasing milling time. In addition, the Ti peaks
move towards larger angle direction as milling con-
tinues indicating that some Si atoms have dissolved
into Ti lattice during milling and formed a HCP
Ti(Si) solid solution. After milling for 30 h, an
amorphous halo appears, but also crystalline Ti(Si)
and Si peaks still exists in the XRD pattern. After
45 h of milling, only the amorphous halo exists in
The morphologies of Ti
Si
powders at dif-
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ferent milling times are shown in Fig. 3. The start-
ing powders have irregular morphologies and their
size distribution is inhomogeneous too. After mill-
ing, the sizes of particles are reduced and their
shape eventually become spherical.
the XRD pattern, indicating that Ti
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ders have completely been transformed into
Si
pow-
Fig. 4 presents the XRD patterns of Ti Si
V
ꢁ\V
powders milled for 45 h. Ti Si , Ti
Si
and
ꢃꢄ ꢅꢄ
ꢆꢅꢇꢄ ꢈꢃꢇꢄ

J. Yang et al. / Physica B 279 (2000) 241}245
243
free energies of amorphous and metastable solid
solution phases in the Ti}Si system. The result was
shown in Fig. 5. It can be seen that the free energy
curve of amorphous phase intersects with that of
solid solution phase. According to the rule of
common tangent, the amorphous phase forming
composition range (AFR) is approximately x "
2*
0.45}0.78, which is consistent with the experimental
result.
Fig. 6 shows the di!erential thermal analysis
(DTA) curve of Ti
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
exothermic peak due to the crystallization of the as
Si
milled for 45 h. An
milled amorphous Ti Si powders was ob-
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
served. It locates between 7603C and 8603C. The
crystallizing temperature was determined to be
7903C.
Fig. 2. TEM micrograph and corresponding electronic di!rac-
tion pattern of Ti Si powders milled for 45 h.
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
By annealing the as-milled Ti}Al powders,
Ti Si amorphize completely, only amorphous
ꢄꢂ ꢄꢂ
Zhang et al. reported that Ti Al intermetallics [17]
was obtained. To explore the possibility of acquir-
ꢈ
halos and no crystalline peaks exist in their pat-
terns; while crystalline Ti and Si peaks remain in
ing Ti}Si system intermetallics, the as-milled
the patterns of Ti
and no intermetallics is found. According to the
Miedema model [15,16], we calculated the Gibbs
Si
and Ti Si powders,
Ti
Si
and Ti
Si
powders were isother-
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
ꢅꢄ ꢃꢄ
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
mally annealed at 8603C for 1 h in sealed vacuum
quartz tube. The XRD patterns of the annealed
Fig. 3. SEM micrographs of Ti
Si
at di!erent milling times: (a) 0; (b) 10; (c) 16; (d) 30 h.
ꢆꢅꢇꢄ ꢈꢃꢇꢄ

244
J. Yang et al. / Physica B 279 (2000) 241}245
Fig. 6. DTA curve of the as-milled Ti
Si
powders.
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
Fig. 4. XRD patterns of Ti Si
powders after milling for 45 h.
V
ꢁ\V
Fig. 7. XRD patterns of Ti
ꢆꢅꢇꢄ ꢈꢃꢇ ꢄ
after vacuum annealing at 8603C for 1 h ((a) Ti
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
Si
and Ti
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
Si
Si
powders
; (b)
Ti
Si
).
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
Fig. 5. Gibbs free energy of Ti}Si system versus Ti concentra-
tion.
The above results show that the Ti}Si system
intermetallics can be obtained by combining MA
method with appropriate heat treatment. However,
one should not take delight in this, since the prob-
lem remains how to consolidate them with high
density and nanostructure. Further studies are
under way.
samples were presented in Fig. 7, it can be seen that
the as-milled Ti
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
have completely transformed to Ti Si and TiSi
Si
and Ti
Si
powders
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
ꢄ
ꢈ
ꢅ
respectively.

J. Yang et al. / Physica B 279 (2000) 241}245
245
4. Conclusion
[3] L.T. Zhang, Ph. D. Thesis, Shanghai Jiao Tong University,
1997.
[4] S. Guo, N. Martellim, N. Burgio et al., J. Mater. Sci. 26
(1990) 6190.
[5] T. Itsukaichi, S. Shiga et al., Mater. Sci. Forum 88}89
(1992) 631.
[6] Cocco, I. Soletta et al., Philos. Mag. 61B (1990) 473.
[7] C. Suryanarayana, G.H. Chen, F.H. Froes, Scripta Metall
Mater. 26 (1992) 1727.
[8] T.R. Smith, K.S. Vecchio, Nanostruct. Mater. 5 (1995) 11.
[9] B.L. Huang, J. Vallone, M.J. Luton, Nanostruct. Mater.
5 (1995) 411.
[10] S.G. Pys, P. Nash, N.J. Kim, Scripta Metall. Mater. 34
(1996) 1231.
[11] Z. Peng, C. Suryanarayana, F.H. Froes, Metall. Mater.
Trans. 27A (1996) 41.
[12] Oehring, R. Bormann, Mater. Sci. Eng. 134A (1991)
1330.
[13] P. Radinski, A. Calka, Mater. Sci. Eng. 134A (1991)
1376.
(1) Elemental powder mixtures of Ti Si
were
V
ꢁꢂꢂ\V
mechanically alloyed in a planetary ball mill.
Ti Si , Ti
were amorphized completely after milling for
45 h, no obvious amorphization was observed
Si
and Ti Si powders
ꢃꢄ ꢅꢄ
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ꢄꢂ ꢄꢂ
for Ti
Si
and Ti Si powders.
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
ꢅꢄ ꢅꢄ
(2) By using the Miedema model, the AFR of
Ti}Si system was calculated, and was found to
be consistent with the experimental AFR.
(3) Annealing the as-milled powders in vacuum at
8603C for 1 h, Ti
powders completely transformed into Ti Si
Si
and Ti
Si
ꢆꢅꢇꢄ ꢈꢃꢇꢄ
ꢈꢈꢇꢈ ꢆꢆꢇꢃ
ꢄ
ꢈ
and TiSi intermetallics, respectively.
ꢅ
[14] D. Oleszak, M. Burzynska-szyszko, H. Matyja, J. Mater.
Sci. Lett. 12 (1993) 3.
References
[1] J.S. Wu, P.A. Beaven, R. Wagner et al., in: C.T. Liu et al.
(Eds.), High Temperature Ordered Intermetallic Alloys
Material Research Society Symposium Proceedings, vol.
133, 1989, p. 761.
[15] R. Miedema, F.R. De Boer, R. Boom, Physics 103B (1981)
67.
[16] J.Y. Yang, T.J. Zhang, K. Cui, X.G. Li, J. Zhang, J. Alloys
Compounds 242 (1996) 153}156.
[2] M. Es-souni, R. Wagner, P.A. Beaven, F.P. Schimansky, R.
Gerling, Scripta Metall. Mater. 26 (1992) 727.
[17] T.J. Zhang, X.G. Li, J.Y. Yang, Mater. Eng. 12 (1993) 27, in
Chinese.