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:
[email protected] 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 Cubic boron nitride (BNc) is the second hardest material after diamond [1]; the former exceeds the latter 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 catalytic technique is more technologically effective, but it allows obtainment of BNc in the form of powder materials 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 compounds, 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 compounds are extremely contradictory. In [5], it was stated that BNc with a size of 5–10 µm interacts in contact with a titanium plate at a temperature 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 + 1/2TiB2 + 3/2C, TiN + BN = TiB2 + 3/2N2 are impossi-
ble. In [7], in the study of the interaction between BNc and titanium and silicon at high pressures and temperatures, 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 pressure, 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]. In this work, we present results of studies of the interaction in the system BNc–Ti in vacuum at temperatures 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 prepared 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 intensity 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 the strongest reflexes of BNh (I002) and BNc (I111) for the initial BNc powder was 0.012, which, according to
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this technique, corresponded to a weight fraction of BNc of 0.998 in the initial powders. The titanium powder corresponded to the PTM-2 brand. Differential Thermal Analysis. The obtained mixtures 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 mixtures was carried out by means of a high-sensitivity thermographic apparatus with recording of the dependence ∆T = f(T) by means of an xy recorder. With a view to calibrate the apparatus, we recorded the DTA curves of analytical grade NaCl (ím = 1074 K, ∆Hm = 28.2 kJ/mol), MPC-2U Cu (Tm = 1356 K, ∆Hm = 13.0 kJ/mol), analytical 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). The experimentally found temperatures of the phase transitions were in good agreement with the ones known from the literature. The error in the determination 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 combined 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 cooling, the samples were taken out and subjected to XPA. 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 exposure at one point of 10 s). 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 Pearson VII 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. Chemical Analysis. The samples were etched in boiling hydrochloric acid for selective removal of titanium [14]; afterwards, they were washed, dried, and weighed. The procedure was repeated with the use of nitric acid for selective removal of titanium diboride INORGANIC MATERIALS
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∆T, arb. units 1
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0 1
(b)
0 1
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0 1200 1250 1300 1350 1400 1450 1500 1550 1600 T, ä Fig. 1. DTA curves of the samples of the system Ti–BNc with a weight fraction of BNc of (a) 0.1, (b) 0.5, and (c) 0.9 (the effect heat is normalized to 1 g of sample).
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 determine the phase and quantitative composition of the samples. RESULTS AND DISCUSSION Differential Thermal Analysis Two heat effects are observed on the DTA curves of the samples of the system Ti–BNc in the temperature range 298–1490 K. The first effect is accompanied by heat absorption at 1150 K, 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 titanium 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. X-Ray Phase Analysis. The XPA of mixtures that had been held at 1100 K, i.e., below the initial exothermic effect temperature, and cooled in the cutoff furnace
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T, K 0 1400
0.2
0.4
0.6
C2, mole fraction BNc 0.8 1.0
1350
1300
1250
1200 0
0.2
0.4
0.6 0.8 1.0 C1, weight fraction BNc
Fig. 2. Dependence of the initial interaction temperature in the system Ti–BNc on content of BNc.
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 strongest 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∆H, J/g 0
0.2
0.4
0.6
C2, mole fraction BNc 0.8 1.0
150
125
100
75 0
0.2
0.4
0.6 0.8 1.0 C1, weight fraction BNc
Fig. 3. Dependence of the specific heat of the process of interaction between BNc and Ti on content of BNc.
ure 6 depicts the dependences of contents of BNh, BNc, and β-Ti, averaged over the results of XPA and chemical analysis, for thermally treated samples on content of BNc in the initial samples. It follows from the given dependences that the BNh content increases significantly 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 dependences of the contents of Ti2N, TiB, TiN, and TiB2, averaged over the results of XPA and chemical analysis, 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 intermediate 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 following stages, BNh and Ti interact with formation of nitrides and borides of titanium. This statement is confirmed by the content of monoboride (TiB), diboride (TiB2), and nitride of titanium (TiN) (Fig. 7). The content 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. 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 BNh, it is known that the transition in vacuum BNc 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 process of holding for 3 min at 1930 K [18]. On the basis of the fact that the temperature of the initial reverse BNh in the system Ti–BNc transition BNc decreases considerably, it is possible to make a conclusion 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 INORGANIC MATERIALS
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INTERACTION BETWEEN BNc AND TITANIUM IN VACUUM I, arb. units 25000
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2450
BNc BNh α-Ti TiN
(74-1906) (73-2095) (44-1294) (38-1420)
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Ti2N (77-1893) TiB2 (35-741) TiB2 (6-641)
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–BNc with a weight fraction of BNc of 0.8 after heating to (a) 1100 and (b) 1470K.
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 80
reverse phase transition region is limited only by the surface of the contact of the BNc and Ti powders; therefore, after the complete transition of the surface BNc layer into the hexagonal structure and subsequent solidphase reactions, the transition slows down. Some discrepancy 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
1
0 0.2 C, weight fraction
3
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C2, mole fraction BNc 0.4 0.6 0.8
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8 0.6
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4 0.2 2 2
0
20 26.6
26.8
27.0 2θ, deg
Fig. 5. Fragment of the diffractograms in the angle range 2θ from 26.4° to 27.0° of samples of the system Ti–BNc with a weight fraction of BNc of (1) 0.9, (2) 0.8, (3) 0.7, (4) 0.6, and (5) 0.5 heated to 1470 K and cooled down to room temperature. INORGANIC MATERIALS
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C × 102, weight fraction
nitrides of titanium in the temperature range under study [5].
0.2 0.4 0.6 0.8 C1, weight fraction BNc
0 1.0
Fig. 6. Dependences of the content of (1) BNc, (2) BNh, and (3) β-Ti in samples heated to 1470 K in vacuum and cooled down to room temperature on content of BNc in initial samples.
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0.2
C2, mole fraction BNc 0.4 0.6 0.8
C, weight fraction
0.4
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4 1
0.3 4
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C × 102, weight fraction
630
5.
2
2
0.1
6.
3 0
0.2 0.4 0.6 0.8 C1, weight fraction BNc
0 1.0 7.
Fig. 7. Dependences of the content of (1) Ti2N, (2) TiB, (3) TiB2, and (4) TiN in samples heated to 1470 K in vacuum and cooled down to room temperature on content of BNc in initial samples.
8.
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. 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 by the reverse phase transition BNc BNh. The weight fraction of BNh in the interacting samples monotonically increases with increasing weight fraction of BNc in the initial samples and reaches 0.06 when the weight fraction of BNc is 0.9 in the initial samples.
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REFERENCES 1. Leger, J.M. and Haines, J., The Search for Superhard Materials, Endeavour, 1997, vol. 21, pp. 121–124. 2. Petrusha, I.A., Features of a cBN-to-Graphite-Like BN Phase Transformation under Pressure, Diamond Relat. Mater., 2000, vol. 9, pp. 1487–1493. 3. Shipilo, V.B., Ignatenko, O.V., Anichenko, N.G., and Azarko, I.I., Crystallization Kinetics of Cubic Boron
17. 18.
Nitride in the B–N–Mg–H–F System, Neorg. Mater., 2005, vol. 41, no. 7, pp. 816–818 [Inorg. Mater. (Engl. Transl.), vol. 41, no. 7 p. 713]. Benko, E., Klimczyk, P., Morgiel, J., Wlochowicz, A., and Barr, T.L., Electron Microscopy Investigations of the cBN–Ti Compound Composites, Mater. Chem. Phys., 2003, vol. 81, no. 2, pp. 336–340. Vishnevskii, A.S., Delevi, V.G., Mukovoz, Yu.A., Ositinskaya, T.D., and Chapalyuk, V.P., Interaction of Boron Nitride with Steels and Titanium, Sinteticheskie Almazy, 1978, no. 4, pp. 17–22. Bondarenko, V.P. and Khalepa, A.P., Thermodynamic Estimation of CBN Interaction with Carbides, Nitrides, and Borides of Transition Metals, Sinteticheskie Almazy, 1979, no. 2, pp. 19–21. Barashkov, G.A., Aizenberg, M.B., Nikitina, T.P., Pesin, V.A., Fel’dgun, L.I., Shkidchenko, A.E., and Martynova, T.Yu., Interaction of BNsph with Titanium and Silicon at High Pressures and Temperatures, Sverkhtverdye Mater., 1990, no. 5, pp. 12–13. Bondarenko, V.P., Khalepa, A.P., and Cherepenina, E.S., Study of the Cubic Boron Nitride Interaction with Transitions Metals and Their Carbides, Sinteticheskie Almazy, 1978, no. 4, pp. 22–25. Mazurenko, A.M., Zhuk, M.M., and Ul’yanova, T.I., Contact Interaction of Titanium and Hard Alloy with Boron Nitride at Extremely High Pressure, Poroshk. Metall. (Kiev), 1978, no. 5, pp. 65–68. Piskoska, E., Lawnicak–Jablonska, K., Demchenko, I.N., Benko, E. and Welter, E., X-Ray Absorption Studies of Phase Formation in a Ti/TiN Coating on Cubic Boron Nitride, J. Alloys Compd., 2004, vol. 362, pp. 171–177. 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. Kharitonova, M.V. and Rivlin, I.Ya., Separate Determination of the Content of hexagonal and Cubic Boron Nitrides in Their Common Presence, Abrazivy Almazy, 1967, no. 5, p. 3. Altomare, A., Burla, M.C., Giacovazzo, C., et al., Quanto: a Rietveld Program for Quantitative Phase Analysis of Polycrystalline Mixtures, J. Appl. Crystallogr., 2001, vol. 34, pp. 392–397. Tarasov, A.V., Metallurgiya titana (Metallurgy of Titanium), Moscow: Akademkniga, 2003. Samsonov, G.V., Serebryakova, T.I., and Neronov, V.A., Boridy (Borides), Moscow: Atomizdat, 1975. 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. Gatilova, E.G., Malogolovets, V.G., Kolesnichenko, G.A., and Kostyuk, B.D., Adgeziya rasplavov (Adhesion of Melts), Kiev: Naukova Dumka, 1974, pp. 135–138. Milleade, H.J., Nave E., and Weller, F.H., Transformation of Cubic Boron Nitride to a Graphitic Form of Hexagonal Boron Nitride, Nature, 1959, vol. 184, no. 4687, p.715. INORGANIC MATERIALS
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