Interaction between BNc and titanium in vacuum

Article abstract of DOI:10.1134/S0020168509060090

The thermal stability of cubic boron nitride in vacuum at temperatures up to 1470 K in contact with titanium is studied by means of the differential thermal, X-ray phase, and chemical analyses. It is found that, in the system Ti-BN_c, the reverse phase transition of boron nitride from the cubic to hexagonal structure, followed by formation of titanium borides and nitrides, is observed.

Full text of DOI:10.1134/S0020168509060090

ISSN 0020-1685, Inorganic Materials, 2009, Vol. 45, No. 6, pp. 626–630. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © B.V. Korzun, O.V. Ignatenko, S.A. Lebedev, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 6, pp. 684–689.
Interaction between BNc and Titanium in Vacuum
B. V. Korzun, O. V. Ignatenko, and S. A. Lebedev
State Scientific Institution Joint Institute for Solid State and Semiconductor Physics of the National Academy of Sciences
of Belarus, Minsk, Belarus
e-mail: Ignatenko@ifttp.bas-net.by
Received February 26, 2008
Abstract—The thermal stability of cubic boron nitride in vacuum at temperatures up to 1470 K in contact with
titanium is studied by means of the differential thermal, X-ray phase, and chemical analyses. It is found that, in
the system Ti–BNc, the reverse phase transition of boron nitride from the cubic to hexagonal structure, followed
by formation of titanium borides and nitrides, is observed.
DOI: 10.1134/S0020168509060090
INTRODUCTION
ble. In [7], in the study of the interaction between BNc
and titanium and silicon at high pressures and tempera-
tures, an increase in the titanium diboride content in the
presence of silicon was mentioned. In [8], it was found
that titanium and BNc with a grain size less than 40 µm
under annealing for 1 h react starting from 1670 K with
formation of TiB2, TiB, and TiN. In [9], it was shown that,
in the course of contact interaction between titanium and a
hard alloy with boron nitride at an extremely high pres-
sure, formation of TiN and titanium borides Ti2B5 and TiB
takes place. In [10], it was stated that nitrides of boron and
titanium do not interact. Under mechanical activation of
titanium and hexagonal boron nitride, titanium nitride and
diboride are formed [11].
Cubic boron nitride (BNc) is the second hardest
material after diamond [1]; the former exceeds the lat-
ter in thermal stability and chemical inertness, and has
gained more and more currency in the tool-making
industry. BNc is obtained, for the most part, by effecting
a phase transition from a hexagonal structure both in
the absence of a catalyst at a pressure of 6–10 GPa and
a temperature of 2500–3500 K [2] and in the presence
of a catalyst at a pressure of 2–6 GPa and a temperature
of 1200–1900 K [3]. The catalyst-free technique allows
obtainment of BNc in the form of plates, being suitable
for further use in industry as a cutting tool. The cata-
lytic technique is more technologically effective, but it
allows obtainment of BNc in the form of powder mate-
rials with a grain size from 10 nm to 2 mm. The powder
materials are used for preparation of a composite from
cubic boron nitride and a binding agent from refractory
metals and their compounds. The most generally used
binding materials are titanium and titaniferous com-
pounds, since their application confers rather high
strength properties and good operational characteristics
to obtained composite materials [4]. However, the
available data on thermal stability of BNc in composite
materials based on titanium and titaniferous com-
pounds are extremely contradictory.
In this work, we present results of studies of the
interaction in the system BNc–Ti in vacuum at temper-
atures up to 1470 K with application of differential
thermal analysis (DTA), X-ray phase analysis (XPA),
and chemical analysis.
EXPERIMENTAL
Obtainment of Samples. For the studies, we pre-
pared mixtures of powders of cubic boron nitride and
titanium with a weight fraction of BNc of 0.1, 0.2, 0.3,
0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 by mechanical mixing in
ethyl alcohol for 2 h. The powder of cubic boron nitride
with a fraction of 5/2 µm was subjected to additional
cleaning from impurities and hexagonal boron nitride
by technique [12]. In order to determine the amount of
BNh in samples based on BNc by XPA, we applied a
technique consisting in the determination of the inten-
sity ratio for the strongest reflexes of BNc and BNh.
With this goal in mind, we preliminarily established
this dependence for mixtures of powders of BNc and
BNh with a preset composition. The intensity ratio for
In [5], it was stated that BNc with a size of 5–10 µm
interacts in contact with a titanium plate at a tempera-
ture of 1400 K in the course of 5 h with formation of
hexagonal boron nitride (BNh); at a temperature of
1600 K, it interacts with formation of titanium nitride.
In [6], on the basis of a thermodynamic estimation of
the interaction between BNc and carbide, nitrides, and
borides of titanium, the conclusion was made that, up to
1500 K, no interaction takes place and that reactions of the
types TiB2 + BN = TiN + 3B and 3/2TiC + BN = TiN + the strongest reflexes of BNh (I002) and BNc (I111) for
1/2TiB2 + 3/2C, TiN + BN = TiB2 + 3/2N2 are impossi- the initial BNc powder was 0.012, which, according to
626

INTERACTION BETWEEN BNc AND TITANIUM IN VACUUM
627
this technique, corresponded to a weight fraction of
BNc of 0.998 in the initial powders. The titanium pow-
der corresponded to the PTM-2 brand.
∆T, arb. units
(‡)
1
Differential Thermal Analysis. The obtained mix-
tures were charged into quartz glass vessels of a special
form (so-called Stepanov vessels), from which air was
evacuated to the residual pressure ꢀ1 × 10–3 Pa. The
charge weight was ꢀ1–1.5 g. The DTA of obtained mix-
tures was carried out by means of a high-sensitivity ther-
mographic apparatus with recording of the dependence
∆T = f(T) by means of an xy recorder. With a view to cali-
brate the apparatus, we recorded the DTA curves of ana-
lytical grade NaCl (ím = 1074 K, ∆Hm = 28.2 kJ/mol),
MPC-2U Cu (Tm = 1356 K, ∆Hm = 13.0 kJ/mol), analyti-
cal grade Na2SO4 (Tm = 1157 K, ∆Hm = 36.8 kJ/mol),
MPF-1 Mg (Tm = 923 K, ∆Hm = 8.5 kJ/mol), and pure
grade NaNO3 (Tm = 580 K, ∆Hm = 15.0 kJ/mol).
0
1
(b)
(c)
0
1
0
1200
1250 1300 1350 1400 1450 1500 1550 1600
T, ä
Fig. 1. DTA curves of the samples of the system Ti–BN
c
The experimentally found temperatures of the phase
transitions were in good agreement with the ones
known from the literature. The error in the determina-
tion of phase transition temperatures was 5ä; that of
the heat effect values was 3–4%. A reference standard
for the recording was annealed reagent grade Al2O3,
which was charged into a similar Stepanov vessel. The
sample and the reference standard were installed into
pockets of a holder of heat-resistant steel, which were
placed into a silite furnace or into a resistance furnace.
The temperature was measured by means of a com-
bined Pt–Pt/Rn thermocouple connected to a V7-34
digital voltmeter. The measurements were carried out in
the temperature range from 298 to 1490 K. After cool-
ing, the samples were taken out and subjected to XPA.
with a weight fraction of BN of (a) 0.1, (b) 0.5, and (c) 0.9
(the effect heat is normalized to 1 g of sample).
c
and boride [15]. After that, the etching procedure was
repeated, but in boiling aqua regia for selective removal
of titanium nitride. Subsequently, with a view to
remove hexagonal boron nitride, the samples were
treated by technique [12]. According to the difference
in the sample weight before and after etching, the
weight of hexagonal boron nitride was determined.
As a result of the procedures performed, we
obtained data on the weight of titanium, boron nitride,
and products of their interaction. Comparison of results
of XPA and chemical analysis made it possible to deter-
mine the phase and quantitative composition of the
samples.
X-Ray Phase Analysis. The diffractograms for
refinement of the structures were obtained by means of
a DRON-4 diffractometer (CuKα radiation, step of
0.01° (0.02°), angular range 20°–140°, time of expo-
sure at one point of 10 s).
RESULTS AND DISCUSSION
Differential ThermalAnalysis Two heat effects are
observed on the DTA curves of the samples of the sys-
tem Ti–BNc in the temperature range 298–1490 K. The
first effect is accompanied by heat absorption at 1150 K,
All computations were made by means of the
QUANTO program [13]. The procedure for refinement
of 36 parameters was implemented by gradual addition
of refined parameters in constant graphical simulation
of the background and profiles of diffraction lines until
stabilization of values of the Rp factor, which ranged
within 8.2–8.5% at the final stage of the refinement.
The structure refinement was conducted by the
Rietveld method. For the computations, as a function of
the diffraction line profile, the PearsonVII function was
selected. The diffractogram background was refined in
a polynomial approximation of sixth order. The
obtained reflexes were compared with identification
data of the initial components and probable products of
the reactions.
which corresponds to the phase transition α-Ti
β-Ti.
The second heat effect accompanied by heat release is due
to the process of interaction between Ti and BNc (Fig. 1).
It is determined that the initial interaction temperature
decreases with increasing weight fraction of BNc (Fig. 2).
The initial interaction temperatures are lower than the tita-
nium melting temperature; that is, a solid-phase process
takes place. In addition, the value of specific heat of the
interaction process ∆H varies: it decreases at a weight
fraction of BNc up to 0.7 and increases at a weight fraction
of BNc in the range from 0.7 to 0.9 (Fig. 3); this may be
due to a change in the character of interaction between
BNc and Ti.
Chemical Analysis. The samples were etched in
boiling hydrochloric acid for selective removal of tita-
nium [14]; afterwards, they were washed, dried, and
X-Ray Phase Analysis. The XPA of mixtures that
weighed. The procedure was repeated with the use of had been held at 1100 K, i.e., below the initial exother-
nitric acid for selective removal of titanium diboride mic effect temperature, and cooled in the cutoff furnace
INORGANIC MATERIALS Vol. 45 No. 6 2009

628
T, K
KORZUN et al.
ure 6 depicts the dependences of contents of BNh, BNc,
C , mole fraction BN
2
c
0
0.2 0.4
0.6
0.8
1.0
and β-Ti, averaged over the results of XPA and chemi-
cal analysis, for thermally treated samples on content of
BNc in the initial samples. It follows from the given
dependences that the BNh content increases signifi-
cantly in compounds with a weight fraction of BNc
higher than 0.5. Simultaneously, at the same content of
BNc in the interacting samples, the presence of β-Ti is
not found. The presence of BNc in all samples counts in
favor of the fact that the interaction reactions have not
proceeded completely. Figure 7 presents the depen-
dences of the contents of Ti2N, TiB, TiN, and TiB2,
averaged over the results of XPA and chemical analy-
sis, for thermally treated samples on the content of BNc
in the initial samples. The decrease in the content of
Ti2N, TiB, TiN, and TiB2 at a weight fraction of BNc
above 0.5 and the simultaneous sharp increase in the
content of BNh testify to the fact that BNh is an interme-
diate product of the interaction between BNc and Ti. It
is possible to assume that, at the initial stages of the
interaction, a catalytic phase transition of cubic boron
nitride into the hexagonal structure occurs; at the fol-
lowing stages, BNh and Ti interact with formation of
nitrides and borides of titanium. This statement is con-
firmed by the content of monoboride (TiB), diboride
(TiB2), and nitride of titanium (TiN) (Fig. 7). The con-
tent of the given interaction products increases as the
weight fraction of BNc grows up to 0.5. In this range,
the region of contact of titanium and cubic boron nitride
increases; herein, the formed reaction products (borides
and nitrides of titanium) are limiting factors. Upon a
further increase in the BNc content, the titanium is
insufficient for the interaction; therefore, the content of
the intermediate reaction product, i.e., BNh, increases
sharply.
1400
1350
1300
1250
1200
0
0.2
0.4
0.6
0.8
1.0
c
C , weight fraction BN
1
Fig. 2. Dependence of the initial interaction temperature in
the system Ti–BN on content of BN .
c
c
mode revealed the presence of α-Ti and BNc and the
absence of additional reflexes, which confirms that the
exothermic heat effect found by the DTA is caused by
the interaction between BNc and Ti. In the course of the
XPA of mixtures that had been held at a temperature of
1470 K and cooled in the cutoff furnace mode, reflexes
corresponding to the compounds BNc, BNh, TiN, Ti2N,
TiB, and TiB2 were observed (Fig. 4). Starting from a
weight fraction of BNc of 0.5, the intensity of the stron-
gest reflex for the hexagonal structure of boron nitride
002 increases with increasing content of BNc in the
original mixtures (Fig. 5), which is indicative of the
presence of the reverse phase transition BNc
BNh.
Chemical Analysis. The results of selective etching
of elemental titanium, borides, nitrides of titanium, and
hexagonal boron nitride confirm the XPA results. Fig-
Generalizing the results of the DTA, XPA, and
chemical analysis, it is possible to conclude that, in the
system Ti–BNc in the temperature range 1220–1377 K,
the reverse phase transition of boron nitride from the
cubic to hexagonal structure occurs, after which
borides and nitrides of titanium are formed. As regards
C , mole fraction BNc
∆H, J/g
2
0
0.2 0.4
0.6
0.8
1.0
the transition in vacuum BNc
BNh, it is known that
150
125
100
its temperature is 1570 K [16]; in the course of holding
for 10 min at 1800 K, the volume of transformation for
the grains with a size of 2–4 µm is on the order of 20%
[17]; a partial phase transition is observed in the pro-
cess of holding for 3 min at 1930 K [18]. On the basis
of the fact that the temperature of the initial reverse
transition BNc
BNh in the system Ti–BNc
decreases considerably, it is possible to make a conclu-
sion that titanium catalyzes the boron nitride phase
transition from the cubic to hexagonal structure; in
addition, this process proceeds with heat release. The
given statement is based on enhancement of the heat
effect upon an increase in the content of hexagonal
boron nitride reaction products (Figs. 3, 6) taking into
account the absence of interaction between borides and
75
0
0.2
0.4
0.6
1
0.8
1.0
c
C , weight fraction BN
Fig. 3. Dependence of the specific heat of the process of
interaction between BN and Ti on content of BN .
c
c
INORGANIC MATERIALS Vol. 45 No. 6 2009

INTERACTION BETWEEN BNc AND TITANIUM IN VACUUM
629
BN (74-1906)
Ti2N (77-1893)
TiB2 (35-741)
TiB2 (6-641)
c
I, arb. units
2500
(‡)
BN (73-2095)
h
α-Ti (44-1294)
TiN (38-1420)
2450
2400
50
0
2125
2100
(b)
200
100
0
20
40
60
80
100
2θ, deg
Fig. 4. Diffractograms of samples of the system Ti–BN with a weight fraction of BN of 0.8 after heating to (a) 1100 and (b) 1470K.
c
c
nitrides of titanium in the temperature range under reverse phase transition region is limited only by the
study [5].
surface of the contact of the BNc and Ti powders; there-
fore, after the complete transition of the surface BNc
layer into the hexagonal structure and subsequent solid-
phase reactions, the transition slows down. Some dis-
crepancy of the obtained results and the data of [5–11],
where it was found that BNc interacts with Ti upon
heating at higher temperatures with formation of other
An increase in content of BNc leads to an increase in
content of BNh being formed as a result of the reverse
phase transition. When titanium prevails in the system,
i.e., at low contents of BNc (weight fraction of 0.1–0.5),
the content of BNh formed depends little on the content
of BNc in the mixture. It may be assumed that the
I, arb. units
C , mole fraction BN
2
c
80
60
40
20
1
0 0.2 0.4
0.6
0.8
1.0
10
3
1
0.8
0.6
0.4
0.2
0
2
8
6
4
2
0
3
4
5
2
26.4
26.6
26.8
27.0
2θ, deg
0
0.2
0.4
0.6
0.8
c
1.0
C , weight fraction BN
1
Fig. 5. Fragment of the diffractograms in the angle range 2θ
from 26.4° to 27.0° of samples of the system Ti–BN with a
c
Fig. 6. Dependences of the content of (1) BN , (2) BN , and (3)
weight fraction of BN of (1) 0.9, (2) 0.8, (3) 0.7, (4) 0.6,
c
h
c
β-Ti in samples heated to 1470 K in vacuum and cooled down
and (5) 0.5 heated to 1470 K and cooled down to room tem-
perature.
to room temperature on content of BN in initial samples.
c
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630
KORZUN et al.
Nitride in the B–N–Mg–H–F System, Neorg. Mater.,
C , mole fraction BN
2
c
2005, vol. 41, no. 7, pp. 816–818 [Inorg. Mater. (Engl.
0
0.2 0.4
0.6
0.8
1.0
10
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0.4
0.3
0.2
0.1
4
2
0
1
4
2
3
0
0.2
0.4
0.6
0.8
c
1.0
C , weight fraction BN
1
Fig. 7. Dependences of the content of (1) Ti N, (2) TiB,
(3) TiB , and (4) TiN in samples heated to 1470 K in vac-
2
2
uum and cooled down to room temperature on content of
BN in initial samples.
c
8. Bondarenko, V.P., Khalepa, A.P., and Cherepenina, E.S.,
Study of the Cubic Boron Nitride Interaction with Tran-
sitions Metals and Their Carbides, Sinteticheskie
Almazy, 1978, no. 4, pp. 22–25.
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reaction products, may be explained by the size effect
influence on the degree and rate of transformation.
Thus, the pattern of interaction in the system Ti–BNc
may be explained by the catalytic influence of titanium
on the reverse phase transition of boron nitride from the
cubic to hexagonal structure.
CONCLUSIONS
In the system Ti–BNc upon heating of a mixture of
powders in the temperature range 1220–1377 K, there
occurs an interaction with formation of hexagonal
boron nitride and borides and nitrides of titanium,
whereupon the initial interaction reaction temperature
decreases with increasing BNc in the original mixture.
11. Kurbatkina, V.V., Eremina, E.N., and Levashov, E.A.,
Influence of Mechanical Activation on the Reactive
Power of an Exothermic Mixture in the Titanium–Boron
Nitride System, Tsvetn. Met. (Moscow), 2003, no. 1,
pp. 73–77.
12. Kharitonova, M.V. and Rivlin, I.Ya., Separate Determi-
nation of the Content of hexagonal and Cubic Boron
Nitrides in Their Common Presence, Abrazivy Almazy,
1967, no. 5, p. 3.
13. Altomare, A., Burla, M.C., Giacovazzo, C., et al.,
Quanto: a Rietveld Program for Quantitative Phase
Analysis of Polycrystalline Mixtures, J. Appl. Crystal-
logr., 2001, vol. 34, pp. 392–397.
The concentration dependence of the specific heat
of the process of interaction between Ti and BNc is of
nonmonotonic character; it linearly decreases at a
weight fraction of BNc in the range from 0.1 to 0.7 and
linearly increases in the range from 0.7 to 0.9.
The interaction between Ti and BNc is accompanied
14. Tarasov, A.V., Metallurgiya titana (Metallurgy of Tita-
by the reverse phase transition BNc
BNh. The
nium), Moscow: Akademkniga, 2003.
weight fraction of BNh in the interacting samples
monotonically increases with increasing weight frac-
tion of BNc in the initial samples and reaches 0.06 when
the weight fraction of BNc is 0.9 in the initial samples.
15. Samsonov, G.V., Serebryakova, T.I., and Neronov, V.A.,
Boridy (Borides), Moscow: Atomizdat, 1975.
16. Gatilova, E.G., Malogolovets, V.G., Kolesnichenko, G.A.,
and Chistyakov, E.M., Metody poluchemiya, svoistva i
primenenie nitridov (Methods of Obtaining, Properties, and
Application of Nitrides), Kiev: IPM AN USSR, 1972, pp.
326–331.
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and Kostyuk, B.D., Adgeziya rasplavov (Adhesion of
Melts), Kiev: Naukova Dumka, 1974, pp. 135–138.
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tion of Cubic Boron Nitride to a Graphitic Form of Hex-
agonal Boron Nitride, Nature, 1959, vol. 184, no. 4687,
p.715.
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INORGANIC MATERIALS Vol. 45 No. 6 2009