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Ti3SiC2—a self-lubricating ceramic
August 2002
Materials Letters 55 (2002) 285 – 289 www.elsevier.com/locate/matlet
Ti3SiC2 — a self-lubricating ceramic Yi Zhang a,*, G.P. Ding a, Y.C. Zhou b, B.C. Cai a a
Thin Film and Microfabrication Open Laboratory of State Educational Department, Information Storage Research Center, Shanghai Jiao Tong University, Shanghai 200030, PR China b Ceramic and Composites Department, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, Shenyang, PR China Received 27 November 2000; received in revised form 4 November 2001; accepted 6 November 2001
Abstract The dry sliding behavior of Ti3SiC2 against itself and diamond was investigated on an oscillating pin on flat tester. A large difference in friction coefficient between Ti3SiC2/Ti3SiC2 and Ti3SiC2/diamond pairs was observed. The friction coefficient of former is 1.16 – 1.43, but that of latter is below 0.1. The low friction coefficient of Ti3SiC2 was attributed to the formation of a film on the Ti3SiC2 tribosurface, which is similar to the behavior of graphite. In the other conditions, Ti3SiC2 was not selflubricated. Although Ti3SiC2 has a layered structure and is anisotropy in chemical bonding, this work demonstrated that it is not intrinsically self-lubricated. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Ti3SiC2; Wear; Self-lubricated
1. Introduction Ti3SiC2 has been the focus of many recent investigations because it combines the merit of both metals and ceramics [1 –4]: its electrical and thermal conductivities exceed those of Ti metal; its resistance to oxidation persists up to 1200 jC and it has tolerance to thermal shock; it has high compressive strength, a high Young’s modulus, and there is evidence for ductility. All these unique properties of Ti3SiC2 are related to its layered structure. Like graphite and MoS2, Ti3SiC2 has a hexagonal structure with a space group of P63/mmc. Besides, Ti3SiC2 is readily machined as graphite [2]; thus, it is proposed that Ti3SiC2
*
Corresponding author. Tel.: +86-21-62932517; fax: +86-2162823631. E-mail address: [email protected] ( Y. Zhang).
is self-lubricating and possesses low friction coefficient. However, currently, reports on the tribological behavior of Ti3SiC2 are limited [5– 7]. In this work, we investigated the tribology behavior of Ti3SiC2 against itself and diamond.
2. Experimental procedure The material used here was synthesized by an insitu hot pressing solid – liquid reaction procedure, which was described elsewhere [8]. The density of the material was higher than 95% of the theoretical value. X-ray diffraction analysis revealed that the Ti3SiC2 content in the material was about 93%. The impurities are SiC, TiC and TiSi2, as shown in Fig. 1. Ti3SiC2 plate specimens of 15 15 5 mm and pin specimens of F 5.5 mm were machined from the original ingots. The friction test was conducted on an
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 3 7 9 - 8
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Y. Zhang et al. / Materials Letters 55 (2002) 285–289
Fig. 1. XRD pattern of Ti3SiC2 sample.
oscillating pin on flat tester (Type EM5CB1-W3, KLAXON, England) under dry conditions at room temperature in air within a relative humidity range of 45 – 60%. The sliding duration was 80 min for Ti3SiC2/Ti3SiC2 pair, and 60 min for graphite plate/ diamond pin and Ti3SiC2 plate/diamond pin pair, respectively. The shape and size of the diamond pin is shown in Fig. 2. The average sliding speed was 13 mm/s. Before the friction test, all specimens were polished in an 800-grit emery paper which corre-
Fig. 2. The schematic of diamond pin.
sponding to the surface roughness of Ra = 3 Am. After the friction test, the tribosurface of specimens was examined in a JEOL scanning electron microscope (SEM). Then the Ti3SiC2 specimens were cleaned in acetone ultrasonically to remove the loose debris, and its cross-section was examined in SEM. The Vickers hardness of Ti3SiC2 specimen was measured using
Fig. 3. Variation of Vickers Hardness as a function of indentation load for Ti3SiC2 ceramic.
Y. Zhang et al. / Materials Letters 55 (2002) 285–289
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Table 1 Experimental results of friction test, in which the sliding speed was 13 mm/s 0.98 N 1.96 N 2.94 N 4.9 N 9.8 N Ti3SiC2/Ti3SiC2 pair 1.43 Ti3SiC2/diamond pair 0.09 Graphite/diamond pair 0.24
1.29 0.08 0.16
1.34 0.08 0.10
1.23 0.07 0.05
1.16 0.06 Failure
Shimadzu tester (Model 150, Shimadzu, Japan) at the loads in the range 0.49 –9.8 N.
3. Results and discussion The microhardness of Ti3SiC2 as a function of applied load is plotted in Fig. 3. The figure demonstrates that the Vickers hardness of Ti3SiC2 material decreased with the indentation load and reached a constant value of about 3.6 GPa between 4.9 and 9.8 N. This measured value is slightly higher than that of Refs. [5] and [9]. The high measured hardness was attributed to the presence of SiC and TiC. The results of friction test are listed in Table 1. The friction coefficient of Ti3SiC2/Ti3SiC2 pair is 1.16– 1.43, which is higher than the typical values for Si3N4, SiC, Al3O4 and ZrO2 under similar conditions, 0.44 –0.90. SEM observations revealed that the adhesive and abrasive wear had occurred during the sliding of Ti3SiC2 against itself, as shown in Fig 4. The adhesive wear and high friction coefficient show that gross junction growth had occurred in the contact Fig. 5. Friction coefficient as a function of sliding time for (a) Ti3SiC2/ Ti3SiC2 pair and (b) Friction coefficients of Ti3SiC2 against diamond under different normal load.
Fig. 4. Typical SEM micrograph of tribosurface for Ti3SiC2/Ti3SiC2 pair.
area. In general, the abrasive wear of ceramics occurs when the difference of hardness between friction-pair components is large [10]. As SiC and TiC are the main impurities of the Ti3SiC2 specimen and their hardness is much higher than that of Ti3SiC2, the abrasive wear of Ti3SiC2/Ti3SiC2 pair was believed to be relating to the presence of SiC and TiC phase. Fig. 5(a) shows the friction coefficients vs. sliding time curves for Ti3SiC2 against itself under different normal loads. It is seen from Fig. 5(a) that under lower load, the friction coefficients of Ti3SiC2/Ti3SiC2 pair had increased gradually to a maxim value and then
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Y. Zhang et al. / Materials Letters 55 (2002) 285–289
removal of surface contamination by friction [11]. From the above results, we may conclude at this point that Ti3SiC2 exhibits similar behavior to other ceramic when sliding against themselves or Ti3SiC2 is not selflubricating. However, the friction coefficient of Ti3SiC2 against diamond under dry sliding condition was only 0.05 –0.1, which was even lower than that of graphite against diamond, as shown in Table 1. The curves in Fig. 5(b) varied contrarily to those in Fig. 5(a). The sliding surfaces of Ti3SiC2 specimen against diamond after different sliding duration were examined in SEM, as shown in Fig. 6. It revealed
Fig. 6. SEM micrographs of tribosurface for the Ti3SiC2 plate against diamond pin under a load of 9.8 N after the sliding duration of (a) 10 s, (b) 10 min and (c) 60 min.
decreased to a steady value with the sliding time; the friction coefficients under high load increased gradually to a steady value. The friction coefficient of Ti3SiC2/Ti3SiC2 pair decrease slightly with the adding of normal load. The curves in Fig. 5(a) follow the general trends of ceramic materials with the friction coefficient of sample increases gradually with the sliding time, which is attributed to the gradual
Fig. 7. SEM micrograph of cross-sectional tribosurface for Ti3SiC2 plate against diamond pin under the load of 1000 g: (a) before and (b) after the ultrasonically cleaning.
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concluded that a self-lubricating film had formed on the surface of Ti3SiC2 during its sliding against diamond pin or Ti3SiC2 ceramic exhibited self-lubricating behavior during dry sliding against diamond pin. The formation mechanism of the film in Fig. 5 is unclear. The curves in Fig. 5(b) suggested that it could be related to the surfacial absorption; however, no obvious enrichment of O element in the film was found in Fig. 6. Investigations into the formation mechanism of film in Fig. 5 are under way.
Fig. 8. A higher magnification micrograph of the tribosurface for Ti3SiC2 plate against diamond pin.
that the formation and delamination of a film had occurred on the surface during the sliding test. When the sliding has just began, there was no film and the original surface could be seen, as shown in Fig. 6(a). With the sliding continuing, a film would form on the surface, as shown in Fig.6(b). The film was plate-like and intact. Corresponding to it, the friction coefficient of Ti3SiC2 is the lowest. When the friction coefficient reached the steady value, the film is thicker, but incomplete, as shown in Fig. 6(c). It showed that the delamination of film had occurred. Then, it could be inferred that the variation of the curves in Fig. 5(b) was related to the formation and delamination of a film on the sliding surface of specimen. It indicated that the low friction coefficient of Ti3SiC2 against diamond be attributed to the formation of film on the surface. The SEM observation on the cross-section of sliding surface confirmed the above conclusion, as demonstrated in Fig. 7. It shows that there was a film adhering strongly to the substrate even after the ultrasonically cleaning procedure. Fig. 8 shows that the surface film would be quasi-transparent under high magnification, which is similar to the property of WS2 self-lubricating film [12]. Hence, it could be
4. Conclusion In this work, the tribology behaviors of Ti3SiC2/ Ti3SiC2 and Ti3SiC2/diamond friction pairs were investigated. The results show that Ti3SiC2 ceramic is not intrinsically self-lubricating. Ti3SiC2 ceramic exhibited rather low friction coefficient during dry sliding against diamond pin because of the formation of self-lubricating film.
References [1] M.W. Barsoum, D. Brodkin, T. El-Raghy, Scr. Mater. 36 (1997) 535. [2] M.W. Barsoum, T. El-Raghy, J. Am. Ceram. Soc. 79 (1996) 1953. [3] I.M. Low, S.K. Lee, B.R. Lawn, J. Am. Ceram. Soc. 81 (1998) 225. [4] T. El-Raghy, M.W. Borsoum, A. Zavaliangos, S.R. Kalidini, J. Am. Ceram. Soc. 82 (1999) 2855. [5] N.F. Gao, Y. Mitameto, D. Zhang, J. Mater. Sci. 34 (1999) 4385. [6] S. Myhra, J.W.B. Summers, E.H. Kisi, Mater. Lett. 39 (1999) 6. [7] T. El-Raghy, P. Blau, M.W. Barsoum, Wear 238 (2000) 125. [8] Y.C. Zhou, Z.M. Sun, S.Q. Chen, Y. Zhang, Mater. Res. Innovations 2 (3) (1998) 142. [9] I.M. Low, J. Eur. Ceram. Soc. 18 (6) (1998) 709. [10] D.H. Buckley, K. Miyoshi, Wear 100 (1984) 333. [11] K. Kato, Tribology of ceramics, Wear 136 (1990) 117. [12] S.V. Prasad, J.S. Zabinski, J. Mater. Sci. Lett. 12 (1993) 1413.
Materials Letters 55 (2002) 285 – 289 www.elsevier.com/locate/matlet
Ti3SiC2 — a self-lubricating ceramic Yi Zhang a,*, G.P. Ding a, Y.C. Zhou b, B.C. Cai a a
Thin Film and Microfabrication Open Laboratory of State Educational Department, Information Storage Research Center, Shanghai Jiao Tong University, Shanghai 200030, PR China b Ceramic and Composites Department, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, Shenyang, PR China Received 27 November 2000; received in revised form 4 November 2001; accepted 6 November 2001
Abstract The dry sliding behavior of Ti3SiC2 against itself and diamond was investigated on an oscillating pin on flat tester. A large difference in friction coefficient between Ti3SiC2/Ti3SiC2 and Ti3SiC2/diamond pairs was observed. The friction coefficient of former is 1.16 – 1.43, but that of latter is below 0.1. The low friction coefficient of Ti3SiC2 was attributed to the formation of a film on the Ti3SiC2 tribosurface, which is similar to the behavior of graphite. In the other conditions, Ti3SiC2 was not selflubricated. Although Ti3SiC2 has a layered structure and is anisotropy in chemical bonding, this work demonstrated that it is not intrinsically self-lubricated. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Ti3SiC2; Wear; Self-lubricated
1. Introduction Ti3SiC2 has been the focus of many recent investigations because it combines the merit of both metals and ceramics [1 –4]: its electrical and thermal conductivities exceed those of Ti metal; its resistance to oxidation persists up to 1200 jC and it has tolerance to thermal shock; it has high compressive strength, a high Young’s modulus, and there is evidence for ductility. All these unique properties of Ti3SiC2 are related to its layered structure. Like graphite and MoS2, Ti3SiC2 has a hexagonal structure with a space group of P63/mmc. Besides, Ti3SiC2 is readily machined as graphite [2]; thus, it is proposed that Ti3SiC2
*
Corresponding author. Tel.: +86-21-62932517; fax: +86-2162823631. E-mail address: [email protected] ( Y. Zhang).
is self-lubricating and possesses low friction coefficient. However, currently, reports on the tribological behavior of Ti3SiC2 are limited [5– 7]. In this work, we investigated the tribology behavior of Ti3SiC2 against itself and diamond.
2. Experimental procedure The material used here was synthesized by an insitu hot pressing solid – liquid reaction procedure, which was described elsewhere [8]. The density of the material was higher than 95% of the theoretical value. X-ray diffraction analysis revealed that the Ti3SiC2 content in the material was about 93%. The impurities are SiC, TiC and TiSi2, as shown in Fig. 1. Ti3SiC2 plate specimens of 15 15 5 mm and pin specimens of F 5.5 mm were machined from the original ingots. The friction test was conducted on an
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 3 7 9 - 8
286
Y. Zhang et al. / Materials Letters 55 (2002) 285–289
Fig. 1. XRD pattern of Ti3SiC2 sample.
oscillating pin on flat tester (Type EM5CB1-W3, KLAXON, England) under dry conditions at room temperature in air within a relative humidity range of 45 – 60%. The sliding duration was 80 min for Ti3SiC2/Ti3SiC2 pair, and 60 min for graphite plate/ diamond pin and Ti3SiC2 plate/diamond pin pair, respectively. The shape and size of the diamond pin is shown in Fig. 2. The average sliding speed was 13 mm/s. Before the friction test, all specimens were polished in an 800-grit emery paper which corre-
Fig. 2. The schematic of diamond pin.
sponding to the surface roughness of Ra = 3 Am. After the friction test, the tribosurface of specimens was examined in a JEOL scanning electron microscope (SEM). Then the Ti3SiC2 specimens were cleaned in acetone ultrasonically to remove the loose debris, and its cross-section was examined in SEM. The Vickers hardness of Ti3SiC2 specimen was measured using
Fig. 3. Variation of Vickers Hardness as a function of indentation load for Ti3SiC2 ceramic.
Y. Zhang et al. / Materials Letters 55 (2002) 285–289
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Table 1 Experimental results of friction test, in which the sliding speed was 13 mm/s 0.98 N 1.96 N 2.94 N 4.9 N 9.8 N Ti3SiC2/Ti3SiC2 pair 1.43 Ti3SiC2/diamond pair 0.09 Graphite/diamond pair 0.24
1.29 0.08 0.16
1.34 0.08 0.10
1.23 0.07 0.05
1.16 0.06 Failure
Shimadzu tester (Model 150, Shimadzu, Japan) at the loads in the range 0.49 –9.8 N.
3. Results and discussion The microhardness of Ti3SiC2 as a function of applied load is plotted in Fig. 3. The figure demonstrates that the Vickers hardness of Ti3SiC2 material decreased with the indentation load and reached a constant value of about 3.6 GPa between 4.9 and 9.8 N. This measured value is slightly higher than that of Refs. [5] and [9]. The high measured hardness was attributed to the presence of SiC and TiC. The results of friction test are listed in Table 1. The friction coefficient of Ti3SiC2/Ti3SiC2 pair is 1.16– 1.43, which is higher than the typical values for Si3N4, SiC, Al3O4 and ZrO2 under similar conditions, 0.44 –0.90. SEM observations revealed that the adhesive and abrasive wear had occurred during the sliding of Ti3SiC2 against itself, as shown in Fig 4. The adhesive wear and high friction coefficient show that gross junction growth had occurred in the contact Fig. 5. Friction coefficient as a function of sliding time for (a) Ti3SiC2/ Ti3SiC2 pair and (b) Friction coefficients of Ti3SiC2 against diamond under different normal load.
Fig. 4. Typical SEM micrograph of tribosurface for Ti3SiC2/Ti3SiC2 pair.
area. In general, the abrasive wear of ceramics occurs when the difference of hardness between friction-pair components is large [10]. As SiC and TiC are the main impurities of the Ti3SiC2 specimen and their hardness is much higher than that of Ti3SiC2, the abrasive wear of Ti3SiC2/Ti3SiC2 pair was believed to be relating to the presence of SiC and TiC phase. Fig. 5(a) shows the friction coefficients vs. sliding time curves for Ti3SiC2 against itself under different normal loads. It is seen from Fig. 5(a) that under lower load, the friction coefficients of Ti3SiC2/Ti3SiC2 pair had increased gradually to a maxim value and then
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Y. Zhang et al. / Materials Letters 55 (2002) 285–289
removal of surface contamination by friction [11]. From the above results, we may conclude at this point that Ti3SiC2 exhibits similar behavior to other ceramic when sliding against themselves or Ti3SiC2 is not selflubricating. However, the friction coefficient of Ti3SiC2 against diamond under dry sliding condition was only 0.05 –0.1, which was even lower than that of graphite against diamond, as shown in Table 1. The curves in Fig. 5(b) varied contrarily to those in Fig. 5(a). The sliding surfaces of Ti3SiC2 specimen against diamond after different sliding duration were examined in SEM, as shown in Fig. 6. It revealed
Fig. 6. SEM micrographs of tribosurface for the Ti3SiC2 plate against diamond pin under a load of 9.8 N after the sliding duration of (a) 10 s, (b) 10 min and (c) 60 min.
decreased to a steady value with the sliding time; the friction coefficients under high load increased gradually to a steady value. The friction coefficient of Ti3SiC2/Ti3SiC2 pair decrease slightly with the adding of normal load. The curves in Fig. 5(a) follow the general trends of ceramic materials with the friction coefficient of sample increases gradually with the sliding time, which is attributed to the gradual
Fig. 7. SEM micrograph of cross-sectional tribosurface for Ti3SiC2 plate against diamond pin under the load of 1000 g: (a) before and (b) after the ultrasonically cleaning.
Y. Zhang et al. / Materials Letters 55 (2002) 285–289
289
concluded that a self-lubricating film had formed on the surface of Ti3SiC2 during its sliding against diamond pin or Ti3SiC2 ceramic exhibited self-lubricating behavior during dry sliding against diamond pin. The formation mechanism of the film in Fig. 5 is unclear. The curves in Fig. 5(b) suggested that it could be related to the surfacial absorption; however, no obvious enrichment of O element in the film was found in Fig. 6. Investigations into the formation mechanism of film in Fig. 5 are under way.
Fig. 8. A higher magnification micrograph of the tribosurface for Ti3SiC2 plate against diamond pin.
that the formation and delamination of a film had occurred on the surface during the sliding test. When the sliding has just began, there was no film and the original surface could be seen, as shown in Fig. 6(a). With the sliding continuing, a film would form on the surface, as shown in Fig.6(b). The film was plate-like and intact. Corresponding to it, the friction coefficient of Ti3SiC2 is the lowest. When the friction coefficient reached the steady value, the film is thicker, but incomplete, as shown in Fig. 6(c). It showed that the delamination of film had occurred. Then, it could be inferred that the variation of the curves in Fig. 5(b) was related to the formation and delamination of a film on the sliding surface of specimen. It indicated that the low friction coefficient of Ti3SiC2 against diamond be attributed to the formation of film on the surface. The SEM observation on the cross-section of sliding surface confirmed the above conclusion, as demonstrated in Fig. 7. It shows that there was a film adhering strongly to the substrate even after the ultrasonically cleaning procedure. Fig. 8 shows that the surface film would be quasi-transparent under high magnification, which is similar to the property of WS2 self-lubricating film [12]. Hence, it could be
4. Conclusion In this work, the tribology behaviors of Ti3SiC2/ Ti3SiC2 and Ti3SiC2/diamond friction pairs were investigated. The results show that Ti3SiC2 ceramic is not intrinsically self-lubricating. Ti3SiC2 ceramic exhibited rather low friction coefficient during dry sliding against diamond pin because of the formation of self-lubricating film.
References [1] M.W. Barsoum, D. Brodkin, T. El-Raghy, Scr. Mater. 36 (1997) 535. [2] M.W. Barsoum, T. El-Raghy, J. Am. Ceram. Soc. 79 (1996) 1953. [3] I.M. Low, S.K. Lee, B.R. Lawn, J. Am. Ceram. Soc. 81 (1998) 225. [4] T. El-Raghy, M.W. Borsoum, A. Zavaliangos, S.R. Kalidini, J. Am. Ceram. Soc. 82 (1999) 2855. [5] N.F. Gao, Y. Mitameto, D. Zhang, J. Mater. Sci. 34 (1999) 4385. [6] S. Myhra, J.W.B. Summers, E.H. Kisi, Mater. Lett. 39 (1999) 6. [7] T. El-Raghy, P. Blau, M.W. Barsoum, Wear 238 (2000) 125. [8] Y.C. Zhou, Z.M. Sun, S.Q. Chen, Y. Zhang, Mater. Res. Innovations 2 (3) (1998) 142. [9] I.M. Low, J. Eur. Ceram. Soc. 18 (6) (1998) 709. [10] D.H. Buckley, K. Miyoshi, Wear 100 (1984) 333. [11] K. Kato, Tribology of ceramics, Wear 136 (1990) 117. [12] S.V. Prasad, J.S. Zabinski, J. Mater. Sci. Lett. 12 (1993) 1413.