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Combustion synthesis and densification of large-scale TiC–xNi cermets
October 2002
Materials Letters 56 (2002) 183 – 187 www.elsevier.com/locate/matlet
Combustion synthesis and densification of large-scale TiC–xNi cermets Xinghong Zhang a,*, Xiaodong He a, Jiecai Han a, Wei Qu a, V.L. Kvalin b b
a Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, China Institute of Structural Macrokinetics, Russian Academy of Sciences, Moscow 142432, Russia
Received 8 May 2000; received in revised form 28 August 2001; accepted 28 November 2001
Abstract Large-scale TiC – xNi cermets with 240-mm diameter were fabricated by self-propagating high-temperature synthesis and combined with pseudo heat isostatic pressing. Combustion-synthesized products consisted of TiC phase and Ni binder phase. Spheroidal TiC particles were enveloped by nearly continuous Ni binder phases. Size of TiC particles decrease with Ni content increase. Synthesized products have excellent mechanical properties and the bending strength of TiC – 20Ni and TiC – 30Ni is close to K151A and K152B, respectively, produced by traditional powder metallurgy technology. D 2002 Published by Elsevier Science B.V. Keywords: Combustion synthesis; Pseudo heat isostatic pressing; Large-scale cermets; Titanium carbide
1. Introduction Combustion synthesis or self-propagating hightemperature synthesis (SHS) [1] provides an attractive, affordable alternative to the conventional methods of producing advanced materials such as advanced ceramics, ceramic composites and intermetallic compounds. The combustion synthesis process must be combined with hot-pressing, extrusion, modified HIPing and shock-wave compaction. Impact forging has been successfully used by LaSalvia et al. [2] to produce dense TiC –Ni cermets. Dunmead et al. [3] synthesized and densified TiC/Ni –Al composites simultaneously by initiating combustion reaction under high pressure. However, scarce information on large-scale cermets obtained by combining SHS process with densification * Corresponding author. Institute of Structural Macrokinetics, Russian Academy of Sciences, Moscow 142432, Russia.
is available [4]. As far as the service properties are concerned, the cermets are highly competitive with tungsten carbide-based hard alloys, which are widely applied for cutting, press tools, dies and wear-resistant machine parts. This paper focuses on the combustion reaction, microstructure and mechanical properties of large-scale tungsten-free Ti– C –Ni systems by combustion synthesis/pseudo heat isostatic pressing (SHS/ PHIP) technique.
2. Experimental procedure A cost-saving technology which combined the process of SHS and hot product compaction under pressure was developed for the large-scale cermets products. Fig. 1 depicts the specially designed installation for this purpose. Its principal part is a hydraulic press (I), which is composed of a pressmold (reactor)
0167-577X/02/$ - see front matter D 2002 Published by Elsevier Science B.V. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 4 3 7 - 8
184
X. Zhang et al. / Materials Letters 56 (2002) 183–187
Fig. 1. A general scheme of the installation for SHS pressing. I: hydraulic press (dashed moving parts); II: press,old (reactor); III: a control panel; IV: system for registration and measurement; V: ventilation system; 1: pressure sensor; and 2: temperature pressure.
(II), a control panel (III), and measuring (IV) and ventilation (V) systems. The applied pressure totals 5 MN, and the weight of the moving parts is 8 tons. High-purity ( > 99.5%) powders of elemental titanium, carbon and nickel were used in this investigation. The average particle sizes for Ti, C and Ni powders were 44 (325 mesh), 44 and 52 Am , respectively. The reactant mixture mixed in a dry mixer for 24 h and dried in a vacuum dry oven for 24 h (363 K) was placed into pressmold-reactor with 240-mm diameter for SHS/PHIP (Fig. 2). The bases of the upper (moving) and lower (static) punches were coated with a heat-insulating element. The green charge weight in
Fig. 2. Scheme of pressmold reactor for SHS/PHIP of large-scale cermets.
Fig. 3. Schematic diagram of process for SHS/PHIP.
the experiments was 5.0 kg. Combustion was initiated with a special electronic gear. During synthesis, impurity gases escape from the reactor through the filter and draining channel. The SHS process was carried out in a closed volume. Completion of combustion was followed by stepwise pressing. The compact formed was pushed out of the die to be cooled and for thermal and mechanical treatment. The combustion synthesis/ pseudo heat isostatic pressing densification process is shown in Fig. 3. Here, t1 and t2 are the end time of combustion and the delay and duration of pressing, respectively. P1 and P2 are the process pressures before and after the completion of combustion, respectively. As-produced disk is produced disk is shown in Fig. 4.
Fig. 4. Macro-photo of TiC – 50Ni SHS disk.
X. Zhang et al. / Materials Letters 56 (2002) 183–187
3. Results and discussions 3.1. Phase constituents of combustion-synthesized large-scale TiC –Ni cermets The X-ray diffraction result for the as-reacted material is shown in Fig. 5. As can be seen, the final products all consisted of both TiC and Ni peaks; TiC and Ni are thermodynamically stable phases, and no Ni – Ti or Ni –Ti –C compounds were detected using X-ray diffraction analysis. Ye et al. [5] reported that the combustion reactions of the Ti50 – C30 – Ni20 system occurred and TiC phase NiTi compound were obtained during mechanical alloying, in which the reaction temperature was not beyond the melting point 1672 jC of Ti. In another study, Wong et al. [6] observed the Ni –Ti compounds (Ni3Ti or NiTi) using time-resolved X-ray diffraction on a Ti –C – 25Ni reactant mixture. This is not at all surprising since the final product depends strongly on the combustion reactions, the exothermic reactions of the Ti – C – Ni system take place as follows:
185
namically stable phases and Ni only as a diluent (Ti + C + nNi ! TiC + nNi + Q) for the high temperature. 3.2. Microstructure of combustion-synthesized largescale TiC– Ni cermets
Ti þ C ! TiC þ 184 KJ=mol
Fig. 6 shows the scanning electron micrographs of polished surface of the products combustion-synthesized TiC –xNi. The resulting microstructures for the TiC – Ni material consist of a spheroidal TiC phase (dark) embedded in a nearly continuous Ni binder (white), the very fine Ni network around the TiC particles should produce a considerable increase in toughness comparing with pure TiC [2]. Moreover, as shown in Fig. 6, the TiC size decreases with an increasing amount of Ni metal from 20 to 50 wt.%. This is explained as follows. With the addition of metals, the combustion temperature becomes lower and the grain size becomes smaller since the grain growth of TiC is an exponential function of the combustion temperature. Also, the liquid metals surrounding TiC grains give rise to the increased diffusion path, reduce the driving force for TiC grain growth, and prevent the sintering between TiC grains to form larger grains. Based upon this result, the importance of Ni being in the liquid phase during densification is not only in the ease of densification, but also in the microstructure evolution of the materials.
The transitional phases will be found for a low combustion temperature, but only the TiC thermody-
3.3. Mechanical properties of combustion-synthesized large-scale TiC– Ni cermets
Fig. 5. X-ray analysis of TiC – xNi products prepared by SHS/PHIP.
The mechanical properties of TiC – xNi cermets used in the present study are shown in Table 1. The density of TiC– Ni composite increased with the rise of Ni content due to the higher density of Ni (8.85 g/ cm3) compared with TiC (4.93 g/cm3). The values of the relative densities were all beyond 94% and reached the maximum value at 20 wt.% Ni addition and then decreased with the increase of Ni. The maximum value of hardness and transverse rupture strength was obtained with the addition of 20 wt.% Ni. This value is a remarkable improvement over the transverse rupture strength of pure TiC with no Ni addition [7]. The hardness and transverse rupture strength decrease when the addition of Ni metal is more than 20 wt.% The transverse rupture strength of
2Ti þ Ni ! Ti2Ni þ 83 KJ=mol Ti þ Ni ! TiNi þ 67 KJ=mol Ti þ 3Ni ! TiNi3 þ 140 KJ=mol
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X. Zhang et al. / Materials Letters 56 (2002) 183–187
Fig. 6. SEM image of TiC – xNi cermets prepared by SHS/PHIP. (a)TiC-20Ni, (b)TiC-30Ni, (c)TiC-40Ni, (d)TiC-50Ni.
TiC– 20Ni and TiC– 30Ni is close to K151A (rb = 1225 MPa) and K152B (rb = 1330 MPa), respectively, produced by traditional powder metallurgy technology [7]. Combustion synthesis process is a costsaving technology and so it is superior to conventional process especially for preparing large-scale cermets.
Table 1 Properties of products by SHS/PHIIP Materials
TiC – 20Ni TiC – 30Ni TiC – 40Ni TiC – 50Ni
Properties q (g cm 3)
g (%)
rb (MPa)
HRA
5.27 5.47 5.72 5.97
96.8 96.2 95.5 94.3
1116 1107 990 876
88.5 86.25 85 84.25
4. Conclusions Large-scale TiC– xNi cermets with Ni contents of 20 –50 wt.% were produced by combining combustion synthesis with pseudo heat isostatic pressing. Combustion-synthesized products consisted of TiC phase and Ni binder phase. Incorporation of Ni into the mixture of Ti/C = 1.0 changes the size of TiC grains and the size of the grain decreases with an increasing amount of metal addition. Hardness and transverse rupture strength test indicate that the properties of the SHS/PHIP materials are within the range of conventionally processed cermets and that the material with 20 wt.% Ni addition is excellent. Acknowledgements This work was supported by the National Science Foundation of China no. 19902003.
X. Zhang et al. / Materials Letters 56 (2002) 183–187
References [1] A.G. Merzhanov, Arch. Combust. 191 (1981) 1. [2] J.C. LaSalvia, D.K. Kim, R.A. Lipsett, M.A. Meyers, Metall. Mater. Trans. A 26A (1995) 3001. [3] S.D. Dunmead, D.W. Ready, C.E. Semler, J.B. Holt, J. Am. Ceram. Soc. 72 (1989) 2318. [4] V.L. Kvanin, V.A. Gorovoi, N.T. Balikhina, I.P. Borovinskaya, A.G. Merzhonov, Int. J. SHS 2 (1993) 56.
187
[5] L.L. Ye, J.Y. Huang, Z.G. Liu, M.X. Quan, Z.Q. Hu, J. Mater. Res. 11 (1996) 2092. [6] J. Wong, E.M. Larson, J.B. Holt, P.A. Waide, B. Rupp, R. Frahm, Science 249 (1990) 1406. [7] L. Wang, Special Ceramics, South-Mid University, Changsha, 1994, p. 499.
Materials Letters 56 (2002) 183 – 187 www.elsevier.com/locate/matlet
Combustion synthesis and densification of large-scale TiC–xNi cermets Xinghong Zhang a,*, Xiaodong He a, Jiecai Han a, Wei Qu a, V.L. Kvalin b b
a Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, China Institute of Structural Macrokinetics, Russian Academy of Sciences, Moscow 142432, Russia
Received 8 May 2000; received in revised form 28 August 2001; accepted 28 November 2001
Abstract Large-scale TiC – xNi cermets with 240-mm diameter were fabricated by self-propagating high-temperature synthesis and combined with pseudo heat isostatic pressing. Combustion-synthesized products consisted of TiC phase and Ni binder phase. Spheroidal TiC particles were enveloped by nearly continuous Ni binder phases. Size of TiC particles decrease with Ni content increase. Synthesized products have excellent mechanical properties and the bending strength of TiC – 20Ni and TiC – 30Ni is close to K151A and K152B, respectively, produced by traditional powder metallurgy technology. D 2002 Published by Elsevier Science B.V. Keywords: Combustion synthesis; Pseudo heat isostatic pressing; Large-scale cermets; Titanium carbide
1. Introduction Combustion synthesis or self-propagating hightemperature synthesis (SHS) [1] provides an attractive, affordable alternative to the conventional methods of producing advanced materials such as advanced ceramics, ceramic composites and intermetallic compounds. The combustion synthesis process must be combined with hot-pressing, extrusion, modified HIPing and shock-wave compaction. Impact forging has been successfully used by LaSalvia et al. [2] to produce dense TiC –Ni cermets. Dunmead et al. [3] synthesized and densified TiC/Ni –Al composites simultaneously by initiating combustion reaction under high pressure. However, scarce information on large-scale cermets obtained by combining SHS process with densification * Corresponding author. Institute of Structural Macrokinetics, Russian Academy of Sciences, Moscow 142432, Russia.
is available [4]. As far as the service properties are concerned, the cermets are highly competitive with tungsten carbide-based hard alloys, which are widely applied for cutting, press tools, dies and wear-resistant machine parts. This paper focuses on the combustion reaction, microstructure and mechanical properties of large-scale tungsten-free Ti– C –Ni systems by combustion synthesis/pseudo heat isostatic pressing (SHS/ PHIP) technique.
2. Experimental procedure A cost-saving technology which combined the process of SHS and hot product compaction under pressure was developed for the large-scale cermets products. Fig. 1 depicts the specially designed installation for this purpose. Its principal part is a hydraulic press (I), which is composed of a pressmold (reactor)
0167-577X/02/$ - see front matter D 2002 Published by Elsevier Science B.V. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 4 3 7 - 8
184
X. Zhang et al. / Materials Letters 56 (2002) 183–187
Fig. 1. A general scheme of the installation for SHS pressing. I: hydraulic press (dashed moving parts); II: press,old (reactor); III: a control panel; IV: system for registration and measurement; V: ventilation system; 1: pressure sensor; and 2: temperature pressure.
(II), a control panel (III), and measuring (IV) and ventilation (V) systems. The applied pressure totals 5 MN, and the weight of the moving parts is 8 tons. High-purity ( > 99.5%) powders of elemental titanium, carbon and nickel were used in this investigation. The average particle sizes for Ti, C and Ni powders were 44 (325 mesh), 44 and 52 Am , respectively. The reactant mixture mixed in a dry mixer for 24 h and dried in a vacuum dry oven for 24 h (363 K) was placed into pressmold-reactor with 240-mm diameter for SHS/PHIP (Fig. 2). The bases of the upper (moving) and lower (static) punches were coated with a heat-insulating element. The green charge weight in
Fig. 2. Scheme of pressmold reactor for SHS/PHIP of large-scale cermets.
Fig. 3. Schematic diagram of process for SHS/PHIP.
the experiments was 5.0 kg. Combustion was initiated with a special electronic gear. During synthesis, impurity gases escape from the reactor through the filter and draining channel. The SHS process was carried out in a closed volume. Completion of combustion was followed by stepwise pressing. The compact formed was pushed out of the die to be cooled and for thermal and mechanical treatment. The combustion synthesis/ pseudo heat isostatic pressing densification process is shown in Fig. 3. Here, t1 and t2 are the end time of combustion and the delay and duration of pressing, respectively. P1 and P2 are the process pressures before and after the completion of combustion, respectively. As-produced disk is produced disk is shown in Fig. 4.
Fig. 4. Macro-photo of TiC – 50Ni SHS disk.
X. Zhang et al. / Materials Letters 56 (2002) 183–187
3. Results and discussions 3.1. Phase constituents of combustion-synthesized large-scale TiC –Ni cermets The X-ray diffraction result for the as-reacted material is shown in Fig. 5. As can be seen, the final products all consisted of both TiC and Ni peaks; TiC and Ni are thermodynamically stable phases, and no Ni – Ti or Ni –Ti –C compounds were detected using X-ray diffraction analysis. Ye et al. [5] reported that the combustion reactions of the Ti50 – C30 – Ni20 system occurred and TiC phase NiTi compound were obtained during mechanical alloying, in which the reaction temperature was not beyond the melting point 1672 jC of Ti. In another study, Wong et al. [6] observed the Ni –Ti compounds (Ni3Ti or NiTi) using time-resolved X-ray diffraction on a Ti –C – 25Ni reactant mixture. This is not at all surprising since the final product depends strongly on the combustion reactions, the exothermic reactions of the Ti – C – Ni system take place as follows:
185
namically stable phases and Ni only as a diluent (Ti + C + nNi ! TiC + nNi + Q) for the high temperature. 3.2. Microstructure of combustion-synthesized largescale TiC– Ni cermets
Ti þ C ! TiC þ 184 KJ=mol
Fig. 6 shows the scanning electron micrographs of polished surface of the products combustion-synthesized TiC –xNi. The resulting microstructures for the TiC – Ni material consist of a spheroidal TiC phase (dark) embedded in a nearly continuous Ni binder (white), the very fine Ni network around the TiC particles should produce a considerable increase in toughness comparing with pure TiC [2]. Moreover, as shown in Fig. 6, the TiC size decreases with an increasing amount of Ni metal from 20 to 50 wt.%. This is explained as follows. With the addition of metals, the combustion temperature becomes lower and the grain size becomes smaller since the grain growth of TiC is an exponential function of the combustion temperature. Also, the liquid metals surrounding TiC grains give rise to the increased diffusion path, reduce the driving force for TiC grain growth, and prevent the sintering between TiC grains to form larger grains. Based upon this result, the importance of Ni being in the liquid phase during densification is not only in the ease of densification, but also in the microstructure evolution of the materials.
The transitional phases will be found for a low combustion temperature, but only the TiC thermody-
3.3. Mechanical properties of combustion-synthesized large-scale TiC– Ni cermets
Fig. 5. X-ray analysis of TiC – xNi products prepared by SHS/PHIP.
The mechanical properties of TiC – xNi cermets used in the present study are shown in Table 1. The density of TiC– Ni composite increased with the rise of Ni content due to the higher density of Ni (8.85 g/ cm3) compared with TiC (4.93 g/cm3). The values of the relative densities were all beyond 94% and reached the maximum value at 20 wt.% Ni addition and then decreased with the increase of Ni. The maximum value of hardness and transverse rupture strength was obtained with the addition of 20 wt.% Ni. This value is a remarkable improvement over the transverse rupture strength of pure TiC with no Ni addition [7]. The hardness and transverse rupture strength decrease when the addition of Ni metal is more than 20 wt.% The transverse rupture strength of
2Ti þ Ni ! Ti2Ni þ 83 KJ=mol Ti þ Ni ! TiNi þ 67 KJ=mol Ti þ 3Ni ! TiNi3 þ 140 KJ=mol
186
X. Zhang et al. / Materials Letters 56 (2002) 183–187
Fig. 6. SEM image of TiC – xNi cermets prepared by SHS/PHIP. (a)TiC-20Ni, (b)TiC-30Ni, (c)TiC-40Ni, (d)TiC-50Ni.
TiC– 20Ni and TiC– 30Ni is close to K151A (rb = 1225 MPa) and K152B (rb = 1330 MPa), respectively, produced by traditional powder metallurgy technology [7]. Combustion synthesis process is a costsaving technology and so it is superior to conventional process especially for preparing large-scale cermets.
Table 1 Properties of products by SHS/PHIIP Materials
TiC – 20Ni TiC – 30Ni TiC – 40Ni TiC – 50Ni
Properties q (g cm 3)
g (%)
rb (MPa)
HRA
5.27 5.47 5.72 5.97
96.8 96.2 95.5 94.3
1116 1107 990 876
88.5 86.25 85 84.25
4. Conclusions Large-scale TiC– xNi cermets with Ni contents of 20 –50 wt.% were produced by combining combustion synthesis with pseudo heat isostatic pressing. Combustion-synthesized products consisted of TiC phase and Ni binder phase. Incorporation of Ni into the mixture of Ti/C = 1.0 changes the size of TiC grains and the size of the grain decreases with an increasing amount of metal addition. Hardness and transverse rupture strength test indicate that the properties of the SHS/PHIP materials are within the range of conventionally processed cermets and that the material with 20 wt.% Ni addition is excellent. Acknowledgements This work was supported by the National Science Foundation of China no. 19902003.
X. Zhang et al. / Materials Letters 56 (2002) 183–187
References [1] A.G. Merzhanov, Arch. Combust. 191 (1981) 1. [2] J.C. LaSalvia, D.K. Kim, R.A. Lipsett, M.A. Meyers, Metall. Mater. Trans. A 26A (1995) 3001. [3] S.D. Dunmead, D.W. Ready, C.E. Semler, J.B. Holt, J. Am. Ceram. Soc. 72 (1989) 2318. [4] V.L. Kvanin, V.A. Gorovoi, N.T. Balikhina, I.P. Borovinskaya, A.G. Merzhonov, Int. J. SHS 2 (1993) 56.
187
[5] L.L. Ye, J.Y. Huang, Z.G. Liu, M.X. Quan, Z.Q. Hu, J. Mater. Res. 11 (1996) 2092. [6] J. Wong, E.M. Larson, J.B. Holt, P.A. Waide, B. Rupp, R. Frahm, Science 249 (1990) 1406. [7] L. Wang, Special Ceramics, South-Mid University, Changsha, 1994, p. 499.