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Synthesis, structure and properties of nanocrystalline nitrides and borides
NanoStrueturedMaterials.Vol.6. pp.353-356.1995 Copyright© 1995ElsevierScienceLtd PrintedintheUSA. Allrightsreserved 0965-9773/95$9.50+ .00
Pergamon 0965-9773(95)00069-0
SYNTHESIS, STRUCTURE AND PROPERTIES OF NANOCRYSTALLINE NITRIDES AND BORIDES R.A.Andrievski t ,G.V.Kalinnikov t ,A.F.Potafeev t ,and V.S.Urbanovich 2
t Institute for New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432, Russia 2 Institute of Solid State Physics and Semiconductors, Belarusian Academy of Sciences, Minsk, 220726, Republic of Belarus
Abstract- The consolidation o f T iN ultrafine powders by application of high pressures and high temperatures is described The evolution of structure and properties is discussed. Results are reported of a hardness test, involving high loads, for characterization of boride PVD films. INTRODUCTION The information on preparation and properties of nanocrystalline materials is very comprehensive (1-4), but regarding high-melting compounds (borides, nitrides, carbides etc) it is not so ample (5,6). Problems of consolidation and nanocrystalline structure formation seem very important both for particulate materials and films. In this connection, ultraline powder consolidation at high pressures and high temperatures and the pecularities of film preparation are the subject of our study. This work is an extension of our previous investigations (7-10), which have also been outlined in reviews (5,6).
CONSOLIDATION OF TITANIUM NITRIDE The compaction and sintering of TiN ultrafine powders have been studied by many authors (7,11-14). However, because of intensive recrystallization, which increased simulataneously with the increase in density, almost dense sintered specimens had essentially grain sizes of about 1 ~tm and more. Hot pressed specimens (T = 1400-1500 °C, P = 40 MPa, t = 5 min) were characterized by a grains size of about 3-25 ~tm; the initial particle size in these experiments was about 60 nm (11). As previously (7,14), TiN plasmachemical powders have been used in our experiments (15). Their specific surface area was 14 m2/g which corresponded to a mean diameter value of about 80 nm; other powder properties, see (7). Compaction was performed in a high-pressure apparatus. Taking into account that TiN ultrafine powders are characterized by a large content of adsorbate gases (14), initial compacts were exposed to vacuum annealing in order to remove gases. Table 1 shows some preliminary results for consolidated powders, measured after highpressure compaction at different temperatures (t = 5 min). 353
354
RA ANDRIEVSKIET AL.
TABLE 1 Some Properies of TiN Ultrafine Powders after Compaction at 4 GPa(a - lattice parameter; d density; W - full width at half maximum of (422) peak; Hv - Vickers microhardness; E Young's modulus; G - elastic shear modulus). T (°C)
a (nm)
d (g/cm3)
900 1000 1130 1200
0.42345 0.42337 0.42344 0.42361
5.15 5.18 5.21 5.24
W* 102 (rad) 1.71 1.37 1.12 1.03
Hv(GPa) at Load(N) 0.5 1 19.6+0.6 21.3+0.4 24.05:1.0 23.5 5:1.1
21.0+0.5 22.0+0.6 24.05:0.9 23.6 5:0.6
E (GVa)
G (GPa)
390+20 4005:20 406+20 412 5:20
163+3 1685:3 1715:3 173 5:3
Let us discuss these results. One can see that some residual porosity (2-4%; theoretical density value about 5.35 g/cm3) is present in the specimens and a density increase with temperature rise is evident. The elastic properties and hardness are also changed practically monotonously with the density. X-ray analysis revealed only one phase (TIN). Some oscillations of a lattice parameter may be connected to the influence of both impurities (carbon, oxygen) and to the nitrogen content after compaction. The microstructure study has revealed the presence of inclusions. Their size ranged from a fraction of a micrometer to some tenths micrometers. The hardness of inclusions was less than that of the main phase, i.e. equal to 10-20 GPa which is also suitable for conventional TiN hardness values (16). The largest inclusions exhibited the least hardness. It seems very likely that these inclusions are a result of TiN dynamic recrystallization. The apperance of these inclusions at 900 -1000°C is very suprising because, as we observed in the study of TiN ultrafine powder sintering (14), at these temperatures almost no shrinkage and change in specific surface area occured. So the temperature at which appreciable dynamic recrystallization manifests is lower than that for the onset of detectable sintering and diffusion processes. As known, X-ray peak narrowing is a result of grain growth and of a decrease in the magnitude of internal stresses. It is interesting that the decrease of the W value is accompanied by a hardness increase which can be related to the largest influence of change in density on hardness. However, at 1200 °C the increase in hardness is stopped. It is evident that there are at least two kinds of grain boundaries in our samples and it seems interesting to study the character of grain boundary distribution, as pointed out by Watanabe (17). These investigations are being continued both as regards the rise of temperature and extension of pressure limits and the evaluation of grain size and structure by XRD, TEM, and SEM methods.
HARDNESS OF BORIDE FILMS
Data on film hardness largely concern titanium nitride (6,10,18). Other interesting highmelting compounds, i.e. titanium boride have not been investigated in detail. However, some data on this question are being elaborated (19-21). We were interested in studying the influence of the conditions of deposition.
NANOCRYSTALLINENITRIOESANDBORIDES
355
Films were deposited by the PVD process (magnetron sputter ion plating) (22). We have used a sintered TiB2 target employing both d.c. and r.f. sputtering. The film thickness was about 1.5-1.7 p.m. One hardness was measured over the large load interval both by the Vickers and the Knoop methods as well as by using a nanoindenter (23). The latter measurement is of special interest because of the small thickness of our films. Table 2 shows the influence of load on hardness for two kinds of films. TABLE 2 Influence of Load on Hardness Values (GPa) for TiB 2 Films Prepared with Different Bias Voltages (I - U = 0; II - U = -30 V) Load (cN) 1 3 5 10 15 25 30 50
NanoVickers I II 29.8 26.6 24.7
Knoop
Vickers
I
II
22.0 21.9 17.0
29.9 25.5 21.0
13.3
136
I
II
36.7 32.2 31.3
21.2 + 1.3 17.2 + 0.6
26.5 + 3.1 19.8 + 1.6
It becomes evident that the size effect is observed in all determinations. It is also evident that the higher hardness values are higher for films II as compared to films I. The influence of bias has also been pointed by Knotek and Loftier (21). At the same time, r.f. sputtering resulted in significantly lower hardness values. Some differences between Vickers and Knoop determinations do not suprise which have been noted in the literature (24). The lower level of nanoindentation results, compared with Vickers and Knoop results can be attributed to the unrelaxed character of these measurements. The higher hardness values for films II may be explained by the pecularities of the microstructures. SEM investigations have revealed that the columnar structure on crosssections was more typical for films II; the grain size on taper-sections was variable in a large range from 0.1 p,m to several micrometers. In these experiments the conventional hard alloys (Hv = 16-18 GPa) have been used as substrates. In the case of TiB2 with single crystals used as substrates (Hv = 4.2 GPa), we obtained for films II an H v value of about 45 + 8 GPa (load, 0.3N). This value agrees with data (20) obtained for TiB 2 films sputtered at the bias voltage -70 V (thickness, 4.1 p.m). It is evident that further studies are needed to elucidate the character of grain boundaries and rational methods of its change in films.
ACKNOWLEDGEMENTS Part of the research described in this publication was possible by grant No. MTF000 from the International Science Foundation.
356
IRA ANORIEVSKIET AL
The authors are grateful to Dr.E.J.Brookes, Dr.S.V.Gurov, Dr.N.P.Kobelev, Dr.S.Ju.Sharivker, and Dr.A.S.Shteinberg as well as Mr.S.A.Amanulla and Mr.V.M.Kuchinski for active help in this work. REFERENCES
1. H.Gleiter, Nanostr.Mater. 1 .,1(1992). 2. C..Suryanarayana and F.H.Froes, Metall.Trans. 23A..,1071(1992). 3. R.Siegel, Nanostr.Mater. 3 .,1(1993). 4. Eds.G.C.Hadjipanayis and R.Siegel, Nanophase Materials:Synthesis -Properties Applications, Ser.E,vol.260, Kluwer Acad.Publ., Dodrecht p.808(1994). 5. R.A.Andrievski, J.Mater.Sci. 29 .,614(1994). 6. R.A.Andrievski, Russ.Chem.Rev. 23 .,431(1994). 7. R.A.Andrievski, V.I.Torbov, and E.N.Kurkin, Proc. 13th Intern. Plansee Seminar'93, Eds.H.Bildstein and R.Eck, Planseewerke, Reutte, vol.3, p.649-656(1993). 8. R.A.Andrievski, V.T.Ivannikov, and V.S.Urbanovich, Proc.Intern.Confer. "Silicon Nitride'93", Eds.M.Hoffmann, P.Becher, and G.Petzow, Key Engin.Mater. 89-91 .,p.445-448(1993). 9. R.A.Andrievski, Int.J.Powd.Metall. 30 .,59(1994) 10. R.A.Andrievski,I.A.Anisimova,and V.P.Anisimov, Thin Solid Films, 205 .,171(1991). 11. V.I.Torbov, V.N.Troitskiy,and A.Z.Rachmatullina, Powd.Metall.(12), 27(1979)(in Russian). 12. P.S.Kislyi and M.A.Kuzenkova, Sintering High-Melting Compounds, p.167,Naukova Dumka, Kiev(1980)(in Russian). 13. Y.Ogino,M.Miki,M.Yamasaki,and T.Inuma, Mater.Sci.Forum 88-90., 795 (1992). 14. R.A.Andrievski, R.A.Lyutikov, O.D.Torbova, V.I.Torbov, V.G.Vil'chinski, O.M.Grebtsova, E.P.Domashneva, A.A.Eremenko, and A.Z.Rakhmatullina, Inorg.Mater. 29.,1474(1993). 15. R.A.Andrievski, V.S.Urbanovich, N.P.Kobelev, V.M.Kuchinski, and A.F.Potafeev, to be published. 16. R.A.Anrdievski and I.I.Spivak, Strength of High-Melting Compounds and Materials on Its Base, p.368, Metallurgia, Cheliabinsk(1989). 17. T.Watanabe, Mechanical Properties and Deformation Behaviour of Materials Having Ultra-Fine Microstructures, Eds.M.Nastasi, D.M.Parkin, and H.Gleiter, Kluwer Acad.Publ., Netherlands, p. 129-134(1993). 18. D.S.Rickerby and A.Matthews, Reviews on Powder Metallurgy and Physical Ceramics, 4, 155(1991). 19. H.Holleck and H.Schulz, Surface and Coatings Techn. 3_fi_6.,707(1988). 20. C.Mitterer,M.Rauter,and P.Rodhammer, ibid 4__L.,351(1990). 21. O.Knotek and F.Loffler, J.Hard Mater. 3 .,29(1992). 22. R.A.Andrievski, S.A.Amanulla, E.J.Brookes, G.V.Kalinnikpv and A.F.Potafeev, to be published. 23. M.F.Doemer and W.D.Nix, J.Mater.Res. 1.,601(1986). 24. I.J.McColm, Ceramic Hardness, p.324, Plenum Press, New York(1990).
Pergamon 0965-9773(95)00069-0
SYNTHESIS, STRUCTURE AND PROPERTIES OF NANOCRYSTALLINE NITRIDES AND BORIDES R.A.Andrievski t ,G.V.Kalinnikov t ,A.F.Potafeev t ,and V.S.Urbanovich 2
t Institute for New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432, Russia 2 Institute of Solid State Physics and Semiconductors, Belarusian Academy of Sciences, Minsk, 220726, Republic of Belarus
Abstract- The consolidation o f T iN ultrafine powders by application of high pressures and high temperatures is described The evolution of structure and properties is discussed. Results are reported of a hardness test, involving high loads, for characterization of boride PVD films. INTRODUCTION The information on preparation and properties of nanocrystalline materials is very comprehensive (1-4), but regarding high-melting compounds (borides, nitrides, carbides etc) it is not so ample (5,6). Problems of consolidation and nanocrystalline structure formation seem very important both for particulate materials and films. In this connection, ultraline powder consolidation at high pressures and high temperatures and the pecularities of film preparation are the subject of our study. This work is an extension of our previous investigations (7-10), which have also been outlined in reviews (5,6).
CONSOLIDATION OF TITANIUM NITRIDE The compaction and sintering of TiN ultrafine powders have been studied by many authors (7,11-14). However, because of intensive recrystallization, which increased simulataneously with the increase in density, almost dense sintered specimens had essentially grain sizes of about 1 ~tm and more. Hot pressed specimens (T = 1400-1500 °C, P = 40 MPa, t = 5 min) were characterized by a grains size of about 3-25 ~tm; the initial particle size in these experiments was about 60 nm (11). As previously (7,14), TiN plasmachemical powders have been used in our experiments (15). Their specific surface area was 14 m2/g which corresponded to a mean diameter value of about 80 nm; other powder properties, see (7). Compaction was performed in a high-pressure apparatus. Taking into account that TiN ultrafine powders are characterized by a large content of adsorbate gases (14), initial compacts were exposed to vacuum annealing in order to remove gases. Table 1 shows some preliminary results for consolidated powders, measured after highpressure compaction at different temperatures (t = 5 min). 353
354
RA ANDRIEVSKIET AL.
TABLE 1 Some Properies of TiN Ultrafine Powders after Compaction at 4 GPa(a - lattice parameter; d density; W - full width at half maximum of (422) peak; Hv - Vickers microhardness; E Young's modulus; G - elastic shear modulus). T (°C)
a (nm)
d (g/cm3)
900 1000 1130 1200
0.42345 0.42337 0.42344 0.42361
5.15 5.18 5.21 5.24
W* 102 (rad) 1.71 1.37 1.12 1.03
Hv(GPa) at Load(N) 0.5 1 19.6+0.6 21.3+0.4 24.05:1.0 23.5 5:1.1
21.0+0.5 22.0+0.6 24.05:0.9 23.6 5:0.6
E (GVa)
G (GPa)
390+20 4005:20 406+20 412 5:20
163+3 1685:3 1715:3 173 5:3
Let us discuss these results. One can see that some residual porosity (2-4%; theoretical density value about 5.35 g/cm3) is present in the specimens and a density increase with temperature rise is evident. The elastic properties and hardness are also changed practically monotonously with the density. X-ray analysis revealed only one phase (TIN). Some oscillations of a lattice parameter may be connected to the influence of both impurities (carbon, oxygen) and to the nitrogen content after compaction. The microstructure study has revealed the presence of inclusions. Their size ranged from a fraction of a micrometer to some tenths micrometers. The hardness of inclusions was less than that of the main phase, i.e. equal to 10-20 GPa which is also suitable for conventional TiN hardness values (16). The largest inclusions exhibited the least hardness. It seems very likely that these inclusions are a result of TiN dynamic recrystallization. The apperance of these inclusions at 900 -1000°C is very suprising because, as we observed in the study of TiN ultrafine powder sintering (14), at these temperatures almost no shrinkage and change in specific surface area occured. So the temperature at which appreciable dynamic recrystallization manifests is lower than that for the onset of detectable sintering and diffusion processes. As known, X-ray peak narrowing is a result of grain growth and of a decrease in the magnitude of internal stresses. It is interesting that the decrease of the W value is accompanied by a hardness increase which can be related to the largest influence of change in density on hardness. However, at 1200 °C the increase in hardness is stopped. It is evident that there are at least two kinds of grain boundaries in our samples and it seems interesting to study the character of grain boundary distribution, as pointed out by Watanabe (17). These investigations are being continued both as regards the rise of temperature and extension of pressure limits and the evaluation of grain size and structure by XRD, TEM, and SEM methods.
HARDNESS OF BORIDE FILMS
Data on film hardness largely concern titanium nitride (6,10,18). Other interesting highmelting compounds, i.e. titanium boride have not been investigated in detail. However, some data on this question are being elaborated (19-21). We were interested in studying the influence of the conditions of deposition.
NANOCRYSTALLINENITRIOESANDBORIDES
355
Films were deposited by the PVD process (magnetron sputter ion plating) (22). We have used a sintered TiB2 target employing both d.c. and r.f. sputtering. The film thickness was about 1.5-1.7 p.m. One hardness was measured over the large load interval both by the Vickers and the Knoop methods as well as by using a nanoindenter (23). The latter measurement is of special interest because of the small thickness of our films. Table 2 shows the influence of load on hardness for two kinds of films. TABLE 2 Influence of Load on Hardness Values (GPa) for TiB 2 Films Prepared with Different Bias Voltages (I - U = 0; II - U = -30 V) Load (cN) 1 3 5 10 15 25 30 50
NanoVickers I II 29.8 26.6 24.7
Knoop
Vickers
I
II
22.0 21.9 17.0
29.9 25.5 21.0
13.3
136
I
II
36.7 32.2 31.3
21.2 + 1.3 17.2 + 0.6
26.5 + 3.1 19.8 + 1.6
It becomes evident that the size effect is observed in all determinations. It is also evident that the higher hardness values are higher for films II as compared to films I. The influence of bias has also been pointed by Knotek and Loftier (21). At the same time, r.f. sputtering resulted in significantly lower hardness values. Some differences between Vickers and Knoop determinations do not suprise which have been noted in the literature (24). The lower level of nanoindentation results, compared with Vickers and Knoop results can be attributed to the unrelaxed character of these measurements. The higher hardness values for films II may be explained by the pecularities of the microstructures. SEM investigations have revealed that the columnar structure on crosssections was more typical for films II; the grain size on taper-sections was variable in a large range from 0.1 p,m to several micrometers. In these experiments the conventional hard alloys (Hv = 16-18 GPa) have been used as substrates. In the case of TiB2 with single crystals used as substrates (Hv = 4.2 GPa), we obtained for films II an H v value of about 45 + 8 GPa (load, 0.3N). This value agrees with data (20) obtained for TiB 2 films sputtered at the bias voltage -70 V (thickness, 4.1 p.m). It is evident that further studies are needed to elucidate the character of grain boundaries and rational methods of its change in films.
ACKNOWLEDGEMENTS Part of the research described in this publication was possible by grant No. MTF000 from the International Science Foundation.
356
IRA ANORIEVSKIET AL
The authors are grateful to Dr.E.J.Brookes, Dr.S.V.Gurov, Dr.N.P.Kobelev, Dr.S.Ju.Sharivker, and Dr.A.S.Shteinberg as well as Mr.S.A.Amanulla and Mr.V.M.Kuchinski for active help in this work. REFERENCES
1. H.Gleiter, Nanostr.Mater. 1 .,1(1992). 2. C..Suryanarayana and F.H.Froes, Metall.Trans. 23A..,1071(1992). 3. R.Siegel, Nanostr.Mater. 3 .,1(1993). 4. Eds.G.C.Hadjipanayis and R.Siegel, Nanophase Materials:Synthesis -Properties Applications, Ser.E,vol.260, Kluwer Acad.Publ., Dodrecht p.808(1994). 5. R.A.Andrievski, J.Mater.Sci. 29 .,614(1994). 6. R.A.Andrievski, Russ.Chem.Rev. 23 .,431(1994). 7. R.A.Andrievski, V.I.Torbov, and E.N.Kurkin, Proc. 13th Intern. Plansee Seminar'93, Eds.H.Bildstein and R.Eck, Planseewerke, Reutte, vol.3, p.649-656(1993). 8. R.A.Andrievski, V.T.Ivannikov, and V.S.Urbanovich, Proc.Intern.Confer. "Silicon Nitride'93", Eds.M.Hoffmann, P.Becher, and G.Petzow, Key Engin.Mater. 89-91 .,p.445-448(1993). 9. R.A.Andrievski, Int.J.Powd.Metall. 30 .,59(1994) 10. R.A.Andrievski,I.A.Anisimova,and V.P.Anisimov, Thin Solid Films, 205 .,171(1991). 11. V.I.Torbov, V.N.Troitskiy,and A.Z.Rachmatullina, Powd.Metall.(12), 27(1979)(in Russian). 12. P.S.Kislyi and M.A.Kuzenkova, Sintering High-Melting Compounds, p.167,Naukova Dumka, Kiev(1980)(in Russian). 13. Y.Ogino,M.Miki,M.Yamasaki,and T.Inuma, Mater.Sci.Forum 88-90., 795 (1992). 14. R.A.Andrievski, R.A.Lyutikov, O.D.Torbova, V.I.Torbov, V.G.Vil'chinski, O.M.Grebtsova, E.P.Domashneva, A.A.Eremenko, and A.Z.Rakhmatullina, Inorg.Mater. 29.,1474(1993). 15. R.A.Andrievski, V.S.Urbanovich, N.P.Kobelev, V.M.Kuchinski, and A.F.Potafeev, to be published. 16. R.A.Anrdievski and I.I.Spivak, Strength of High-Melting Compounds and Materials on Its Base, p.368, Metallurgia, Cheliabinsk(1989). 17. T.Watanabe, Mechanical Properties and Deformation Behaviour of Materials Having Ultra-Fine Microstructures, Eds.M.Nastasi, D.M.Parkin, and H.Gleiter, Kluwer Acad.Publ., Netherlands, p. 129-134(1993). 18. D.S.Rickerby and A.Matthews, Reviews on Powder Metallurgy and Physical Ceramics, 4, 155(1991). 19. H.Holleck and H.Schulz, Surface and Coatings Techn. 3_fi_6.,707(1988). 20. C.Mitterer,M.Rauter,and P.Rodhammer, ibid 4__L.,351(1990). 21. O.Knotek and F.Loffler, J.Hard Mater. 3 .,29(1992). 22. R.A.Andrievski, S.A.Amanulla, E.J.Brookes, G.V.Kalinnikpv and A.F.Potafeev, to be published. 23. M.F.Doemer and W.D.Nix, J.Mater.Res. 1.,601(1986). 24. I.J.McColm, Ceramic Hardness, p.324, Plenum Press, New York(1990).