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Damping capacity of in situ TiB2 particulates reinforced aluminium composites with Ti addition
Materials & Design Materials and Design 28 (2007) 628–632 www.elsevier.com/locate/matdes
Damping capacity of in situ TiB2 particulates reinforced aluminium composites with Ti addition Yijie Zhang, Naiheng Ma, Haowei Wang *, Yongkang Le, Xianfeng Li The State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, 1954 Huashan Road, Shanghai 200030, PR China Received 5 April 2005; accepted 21 July 2005 Available online 19 September 2005
Abstract The damping capacity of in situ aluminium (Al)/TiB2 composite and composite with Ti excess was investigated. The composites were fabricated with an exothermic reaction process via K2TiF4 and KBF4 salts. The damping behavior of materials over a temperature range of 30–300 C was investigated using a dynamic mechanical thermal analyzer. Experimental findings indicate that damping capacity of composite with Ti excess is lower than that of Al/5 wt% composite when temperature below 110 C and higher than of Al/5 wt% composite above 110 C. The main effect of Ti is the formation of thin layer on TiB2 particulates resulted in the change of damping capacity. 2005 Elsevier Ltd. All rights reserved. Keywords: Damping; Composites; Interface; Aluminum
1. Introduction Recently, in situ metal matrix composites (MMCs) reinforced by ceramic particulates have attracted considerable interests due to their many advantages, such as fine reinforcements and well distribution, having good bonding with the matrix and the cleaner reinforcement/matrix interface. Aluminium (Al) and aluminium-based alloys, mainly due to their low melting point, low density, reasonably high thermal conductivity, heat treatment capability, processing flexibility and their low cost, have been chosen as the matrix materials [1–3]. As for the reinforcement, especially in recent years, TiB2 reinforced aluminum MMCs have been extensively investigated [4–6]. TiB2 is chosen since it is particularly suitable as reinforcement for Al-based reactive sintered composites due to its high exothermic formation and thermodynamic stability in Al [1,2]. In *
Corresponding author. Tel.: +86 21 62932004. E-mail address: [email protected] (H. Wang).
0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.07.015
addition, TiB2 is well known for its high stiffness and hardness, in contrast to most ceramics. Thus, the addition of TiB2 to a metal matrix can greatly improve stiffness, hardness, and wear resistance without apparent loss of thermal expansion coefficient and electrical and thermal conductivities as compared to other ceramic reinforcements [7,8]. With the advent of advanced technology of in situ MMCs, it became possible to combine the high strength with high damping capacity because of increasing of dislocation density and interface. The purpose of this paper aims to present new results of improvement in damping capacity of aluminum by investigating in situ Al/TiB2 composite and composite with Ti addition. The effects of in situ particulates in MMCs and excess Ti on the resultant damping behavior were investigated on the basis of damping measurements conducted on a dynamic mechanical thermal analyzer (DMTA). The intrinsic damping mechanisms in composites were discussed in light of damping data.
Y. Zhang et al. / Materials and Design 28 (2007) 628–632
2. Experimental procedure In the present study, Al/TiB2 composites were fabricated with an exothermic reaction process via K2TiF4 and KBF4 salts. For investigating the effect of particulate content, Al/5 wt%TiB2 composite and Al/ 8 wt%TiB2 composite were produced. In addition, Al/ 5 wt%TiB2 composite with 0.1 wt% Ti excess was produced in order to studying the effect of Ti by Al–Ti master alloy addition. Micro-structural analyses of Al/5 wt%TiB2 composite were carried out on a Phillips EM420 transmission electron microscope (TEM); thin foils were prepared by the ion-milling technique. Because of the amount of TiB2 is too less to detect for phase determination by X-ray diffraction (XRD). In situ TiB2 powers were extracted from the Al/TiB2 composite by dissolving the matrix material in 30% NaOH water solution and followed by counteracting with HCl solution. Observation of particulates morphology was carried out on a Phillips XL30 scanning electron microscope (SEM) and XRD were employed for particulate confirmation. The damping capacity measurements were performed on DMTA using three-point bending testing mode. Rectangular bar samples for the damping capacity measurements with dimensions of 50 · 5 · 1 mm were obtained by spark machining. The measure of damping capacity utilized is loss tangent (tan /) in this study, at least three samples for each testing mode were tested to verify repeatability. The damping capacity, in terms of loss tangent (tan /), is according calculated from tan / ¼ E00 =E0 ; 00
ð1Þ 0
where E is loss modulus and E is storage modulus or dynamic modulus. Commonly used measures to report damping capacity include inverse quality factor (Q1),
629
loss factor (g), loss angle (/), loss tangent (tan /), logarithmic decrement (d) and specific damping capacity (SDC, w). They are interchangeable with a proper conversion for case of relative small damping capacity (tan / < 0.1) by the following equation [9]: Q1 ¼ g ¼ / ¼ tanð/Þ ¼ d=p ¼ w=2p.
ð2Þ
3. Results and discussion Fig. 1 shows TEM bright field (BF) image of Al/ 5 wt%TiB2 composite and corresponding selected area diffraction pattern (SADP). Particulate of hexagonal in shape as shown in Fig. 1(a) was TiB2 phase according to SADP (Fig. 1(b)). It can be seen that there is a cleaner interface between TiB2 particulate and Al matrix, the sharply edge observed herein also confirms that in situ TiB2 particulate is stability in molten aluminum at high temperature. Fig. 2 confirms that the powers extracted from composite were in situ TiB2 particulates. It can be seen from Fig. 3 that the particulate morphology displays on typical characteristic of TiB2 and its size is less than 1 lm. Evidences mentioned above confirm that TiB2 particulates reinforced Al MMCs were produced successfully at present study. The damping capacity of Al/5 wt%TiB2 composite, Al/8 wt%TiB2 composite and purity aluminum as-cast state, as a function of temperature during heating, is shown in Fig. 4. The strain amplitude keeps on 5 · 105 consistently and testing frequency is 1 Hz for temperature sweep test. Increasing the temperature, the damping capacity of these three materials is increased over the studied temperature range. It should be noted that the damping capacity of Al/8 wt%TiB2 composite is higher than that of purity aluminum and
Fig. 1. TEM BF image of Al/5 wt%TiB2 composite (a) and corresponding SADP (b).
630
Y. Zhang et al. / Materials and Design 28 (2007) 628–632 1000
ο
Intensity
800
ο TiB2
600
ο 400
ο
ο
200
ο
ο 10
20
30
40
50
60
70
ο
80
ο 90
2θ (degree)
Fig. 2. XRD pattern of in situ TiB2 particulates.
Fig. 3. Morphologies of in situ TiB2 particulates.
e ¼ DaDT ;
0.03
Al/ 5wt.% TiB2 Purity Aluminum
Tan (φ)
ð3Þ
where Da is the difference between the CTEs of reinforcement and matrix and DT is the temperature change during solidification of MMCs. According to the Granato-Lu¨cke dislocation theory [17], material damping is related to dislocations by the following equations:
Al/ 8wt.% TiB2 0.02
Al/5 wt%TiB2 composite over the studied temperature range. Interestingly, the damping capacity of purity aluminum and Al/5 wt%TiB2 composite has no obvious difference when temperature less than 85 C. The tendency of damping capacity for the three materials has little increase with increasing temperature at first, and when above 85 C, is decidedly temperature-dependent. Zhang and co-workers [9–11] had reported the possible dominant damping mechanisms for particulate reinforced Al MMCs at low temperatures are matrix dislocation damping, intrinsic damping of reinforcing particulate, and particulate/matrix interface damping is likely to be responsible at high temperatures. TiB2 reinforced Al MMCs differ from Gr particulate reinforced Al composites [9,12], in which intrinsic damping mechanism may be ruled out, because TiB2 particulates have lower damping capacity and were impossible to be deformed to dissipate vibration energy. Thus at relatively low temperature the damping capacity of Al/ TiB2 composite has related to dislocation damping. Vogelsang and Arsenault [13–15] had reported that a well-defined dislocation network in the vicinity of the reinforcement/matrix interface may be occurred in particulates reinforced MMCs. The origin of these dislocations is generally attributed to the difference in the coefficient of thermal expansion mismatch (CTE) of the metal matrix and that of the reinforcements. The CTE for TiB2 is 7.2 (in units of 106 C1), whereas a value of 24 is generally reported for aluminum. It is expected that such a large difference in CTE between matrices and reinforcements could generate a high density of dislocations during solidification of the MMCs. Consequently, these become a possible source of high damping capacity because of the motion of the dislocation under cyclic stress. The residual strain, or strain accumulation, produced as a result of the thermal mismatch, may be calculated from [16]
Q1 ¼ ðC 1 =e0 Þ expðC 2 =e0 Þ;
ð4Þ
0.01
0.00 50
100
150
200
Temp (°C)
Fig. 4. Damping capacity spectrum as a function of temperature for purity aluminum, Al/5 wt%TiB2 composite, Al/8 wt%TiB2 composite with testing frequency of 1 Hz.
where e0 is the strain amplitude, C1 and C2 are material constants and C1 is proportional to dislocation density in matrix. Eq. (4) shows that damping capacity is proportional to dislocation density. The contribution of dislocations to damping may be expected to fall with increasing temperature, as their concentration is decreased [14]. From materials point of view, introduce TiB2 particulates into Al matrix can cause dislocation density
Y. Zhang et al. / Materials and Design 28 (2007) 628–632
increasing, subsequently result in improvement in damping capacity. But Fig. 4 shows damping capacity of Al/ 5 wt%TiB2 composite and purity aluminum has the same level at relatively low temperature. The reason maybe there is not enough dislocation in matrix to cause improvement in damping capacity. With content of TiB2 increasing, the dislocation density is increasing. According to Eq. (4), the more dislocations in materials, the better damping capacity is. To some extent Al/ 8 wt%TiB2 composite with higher damping capacity may explain this very well. Also Fig. 4 indicates that at high temperature damping of MMCs are much higher than that of purity aluminum. As mentioned above, interface plays dominant role on improvement of damping capacity. At present study micron TiB2 particulates give rise to much more interface to MMCs than macro particulate reinforced MMCs. For further studying the effect of TiB2/matrix interface, damping capacity of Al/5 wt%TiB2 composite with 0.1 wt% Ti excess was obtained, as shown in Fig. 5. The idea of studying excess Ti stems from grain refinement of aluminum and aluminum alloy. In Al–Ti–B master alloy, there is some evidence that the TiB2 particulates can nucleate Al3Ti (which then nucleates a-Al) and a thin layer of Al3Ti coats the boride when sufficient excess Ti is present [18]. It is found that there is an orientation relationship between the aluminide and the boride [19]: f1 1 2gAl3 Ti kf0 0 0 1gTiB2 and h1 1 2 0iTiB2 kh2 0 1iAl3 Ti or h1 1 0iAl3 Ti . And orientation relationship between aluminum and Al3Ti is f1 1 1ga-Al kf1 1 2gAl3 Ti and h1 1 0ia-Al kh2 0 1iAl3 Ti or h1 1 0iAl3 Ti . The most important role of excess Ti in the melt is that it permits the formation of a thin layer of Al3Ti on the boride particles. As the Ti content is increased to take the overall composition of the melt into the two phase region in the phase diagram, the Al3Ti layers
0.03
Tan (φ)
0.02
Al/ 5wt.% TiB2 Al/ 5wt.% TiB2 with Ti excess
0.01
0.00
50
100
150 15
200
Temp (°C) Fig. 5. Comparison of damping capacity between Al/5 wt%TiB2 composite and Al/5 wt%TiB2 composite with Ti excess.
631
thicken to form particles [19]. In this case, excess Ti will play another role other than as a thin layer of Al3Ti. It can be seen from Fig. 5 that at low temperature Al/ 5 wt%TiB2 composite has higher damping capacity than that of composite with Ti excess and at relatively high temperature, on the contrary, damping of composite with Ti excess is higher than that of Al/5 wt%TiB2 composite. These may be due to at low temperature solution atoms, such as Ti, pin dislocation line so as to decline the length of dislocation line participated bowed movement during dissipate vibration energy and then result in decreasing in damping capacity. At high temperature appropriate excess Ti formed thin layer of Al3Ti on TiB2 particulates plays dominant role on improving damping capacity. Just as Tam and Tjong [20] reported line defects give rise to damping level in the intermediate to high range and surface defects in the high range.
4. Conclusion Introduced in situ TiB2 particulates into aluminum can cause improvement in damping capacity at relatively low temperature on condition that TiB2 content is more enough to produce large amounts of dislocations contributed to damping capacity increasing. Appropriate excess Ti in Al/TiB2 composite can improve damping capacity at relatively high temperature for it forms a thin layer of Al3Ti on TiB2 particulate and decrease damping capacity at low temperature for Ti atoms pin and limit dislocation line movement during dissipate vibration energy.
References [1] Gotman I, Koczak MJ, Shtessel E. Fabrication of Al matrix in situ composites via self-propagating synthesis. Mater Sci Eng A 1994;187:189–99. [2] Brinkman HJ, Duszczyk J, Katgerman L. In-situ formation of TiB2 in a P/M aluminum matrix. Scr Mater 1997;37:293–7. [3] Lloyd DJ. Particle reinforced aluminium and magnesium matrix composites. Int Mater Rev 1994;39:1–23. [4] Ma ZY, Tjong SC. High temperature creep behavior of in situ TiB2 particulate reinforced copper-based composite. Mater Sci Eng A 2000;284:70–6. [5] Biselli C, Morris D, Randall G. Mechanical alloying of highstrength copper alloys containing TiB2 and Al2O3 dispersoid particles. Scr Metall Mater 1994;30:1327–32. [6] Lu¨ L, Lai MO, Su Y, Teo HL, Feng CF. In situ TiB2 reinforced Al alloy composites. Scr Mater 2001;45:1017–23. [7] Smith AV, Chung DDL. Titanium diboride particle-reinforced aluminum with high wear resistance. J Mater Sci 1996;31:5961–73. [8] Viswanadham RK, Mannan SK, Kumar KS, Wolfenden A. Elastic modulus of NiAl TiB2 composites in the temperature range 300 to 1273 K. J Mater Sci Lett 1989;8:409–10. [9] Zhang J, Perez R, Lavernia J. Damping behavior of particulate reinforced 2519 Al metal matrix composites. Scr Metall Mater 1993;28:91–6.
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Y. Zhang et al. / Materials and Design 28 (2007) 628–632
[10] Zhang J, Perez RJ, Lavernia EJ. Documentation of damping capacity of metallic, ceramic and metal-matrix composite materials. J Mater Sci 1993;28:2395–404. [11] Zhang J, Perez RJ, Lavernia EJ. Effect of SiC and graphite particulates on the damping behavior of metal matrix composites. Acta Metall Mater 1994;42:395–409. [12] Wei JN, Cheng HF, Zhang YF, Han FS, Zhou ZC, Shui JP. Effects of macroscopic graphite particulates on the damping behavior of commercially pure aluminum. Mater Sci Eng A 2002;325:444–53. [13] Vogelsang M, Arsenault R, Fisher J. In situ HVEM study of dislocation generation at Al/SiC interfaces in metal matrix composites. Metall Trans A 1986;17:379–89. [14] Arsenault R, Shi J. Dislocation generation due to differences between the coefficients of thermal expansion. Mater Sci Eng A 1986;81:175–87.
[15] Arsenault R, Fisher J. Microstructure of fiber and particulate SiC in 6061Al composites. Scr Metall 1983;17:67–71. [16] Zhang J, Perez R, Lavernia J. Dislocation-induced damping in metal matrix composites. J Mater Sci 1993;28:835–46. [17] Granato A, Lu¨cke K. Theory of mechanical damping due to dislocations. J Appl Phys 1956;27:583. [18] Mohanty P, Gruzleski S. Mechanism of grain refinement in aluminum. Acta Metall Mater 1995;43:2001–12. [19] Schumacher P, Greer A, Worth L, Evans J, Kearns PV, Fisher MA, et al. New studies of nucleation mechanisms in aluminium alloys: implications for grain refinement practice. Mater Sci Technol 1998;14:394–404. [20] Tam KF, Tjong SC. Internal friction and dynamic YoungÕs modulus of aluminium composites reinforced in situ with TiB2 and Al2O3 particulates. Mater Sci Technol 2004;20: 1055–8.
Damping capacity of in situ TiB2 particulates reinforced aluminium composites with Ti addition Yijie Zhang, Naiheng Ma, Haowei Wang *, Yongkang Le, Xianfeng Li The State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, 1954 Huashan Road, Shanghai 200030, PR China Received 5 April 2005; accepted 21 July 2005 Available online 19 September 2005
Abstract The damping capacity of in situ aluminium (Al)/TiB2 composite and composite with Ti excess was investigated. The composites were fabricated with an exothermic reaction process via K2TiF4 and KBF4 salts. The damping behavior of materials over a temperature range of 30–300 C was investigated using a dynamic mechanical thermal analyzer. Experimental findings indicate that damping capacity of composite with Ti excess is lower than that of Al/5 wt% composite when temperature below 110 C and higher than of Al/5 wt% composite above 110 C. The main effect of Ti is the formation of thin layer on TiB2 particulates resulted in the change of damping capacity. 2005 Elsevier Ltd. All rights reserved. Keywords: Damping; Composites; Interface; Aluminum
1. Introduction Recently, in situ metal matrix composites (MMCs) reinforced by ceramic particulates have attracted considerable interests due to their many advantages, such as fine reinforcements and well distribution, having good bonding with the matrix and the cleaner reinforcement/matrix interface. Aluminium (Al) and aluminium-based alloys, mainly due to their low melting point, low density, reasonably high thermal conductivity, heat treatment capability, processing flexibility and their low cost, have been chosen as the matrix materials [1–3]. As for the reinforcement, especially in recent years, TiB2 reinforced aluminum MMCs have been extensively investigated [4–6]. TiB2 is chosen since it is particularly suitable as reinforcement for Al-based reactive sintered composites due to its high exothermic formation and thermodynamic stability in Al [1,2]. In *
Corresponding author. Tel.: +86 21 62932004. E-mail address: [email protected] (H. Wang).
0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.07.015
addition, TiB2 is well known for its high stiffness and hardness, in contrast to most ceramics. Thus, the addition of TiB2 to a metal matrix can greatly improve stiffness, hardness, and wear resistance without apparent loss of thermal expansion coefficient and electrical and thermal conductivities as compared to other ceramic reinforcements [7,8]. With the advent of advanced technology of in situ MMCs, it became possible to combine the high strength with high damping capacity because of increasing of dislocation density and interface. The purpose of this paper aims to present new results of improvement in damping capacity of aluminum by investigating in situ Al/TiB2 composite and composite with Ti addition. The effects of in situ particulates in MMCs and excess Ti on the resultant damping behavior were investigated on the basis of damping measurements conducted on a dynamic mechanical thermal analyzer (DMTA). The intrinsic damping mechanisms in composites were discussed in light of damping data.
Y. Zhang et al. / Materials and Design 28 (2007) 628–632
2. Experimental procedure In the present study, Al/TiB2 composites were fabricated with an exothermic reaction process via K2TiF4 and KBF4 salts. For investigating the effect of particulate content, Al/5 wt%TiB2 composite and Al/ 8 wt%TiB2 composite were produced. In addition, Al/ 5 wt%TiB2 composite with 0.1 wt% Ti excess was produced in order to studying the effect of Ti by Al–Ti master alloy addition. Micro-structural analyses of Al/5 wt%TiB2 composite were carried out on a Phillips EM420 transmission electron microscope (TEM); thin foils were prepared by the ion-milling technique. Because of the amount of TiB2 is too less to detect for phase determination by X-ray diffraction (XRD). In situ TiB2 powers were extracted from the Al/TiB2 composite by dissolving the matrix material in 30% NaOH water solution and followed by counteracting with HCl solution. Observation of particulates morphology was carried out on a Phillips XL30 scanning electron microscope (SEM) and XRD were employed for particulate confirmation. The damping capacity measurements were performed on DMTA using three-point bending testing mode. Rectangular bar samples for the damping capacity measurements with dimensions of 50 · 5 · 1 mm were obtained by spark machining. The measure of damping capacity utilized is loss tangent (tan /) in this study, at least three samples for each testing mode were tested to verify repeatability. The damping capacity, in terms of loss tangent (tan /), is according calculated from tan / ¼ E00 =E0 ; 00
ð1Þ 0
where E is loss modulus and E is storage modulus or dynamic modulus. Commonly used measures to report damping capacity include inverse quality factor (Q1),
629
loss factor (g), loss angle (/), loss tangent (tan /), logarithmic decrement (d) and specific damping capacity (SDC, w). They are interchangeable with a proper conversion for case of relative small damping capacity (tan / < 0.1) by the following equation [9]: Q1 ¼ g ¼ / ¼ tanð/Þ ¼ d=p ¼ w=2p.
ð2Þ
3. Results and discussion Fig. 1 shows TEM bright field (BF) image of Al/ 5 wt%TiB2 composite and corresponding selected area diffraction pattern (SADP). Particulate of hexagonal in shape as shown in Fig. 1(a) was TiB2 phase according to SADP (Fig. 1(b)). It can be seen that there is a cleaner interface between TiB2 particulate and Al matrix, the sharply edge observed herein also confirms that in situ TiB2 particulate is stability in molten aluminum at high temperature. Fig. 2 confirms that the powers extracted from composite were in situ TiB2 particulates. It can be seen from Fig. 3 that the particulate morphology displays on typical characteristic of TiB2 and its size is less than 1 lm. Evidences mentioned above confirm that TiB2 particulates reinforced Al MMCs were produced successfully at present study. The damping capacity of Al/5 wt%TiB2 composite, Al/8 wt%TiB2 composite and purity aluminum as-cast state, as a function of temperature during heating, is shown in Fig. 4. The strain amplitude keeps on 5 · 105 consistently and testing frequency is 1 Hz for temperature sweep test. Increasing the temperature, the damping capacity of these three materials is increased over the studied temperature range. It should be noted that the damping capacity of Al/8 wt%TiB2 composite is higher than that of purity aluminum and
Fig. 1. TEM BF image of Al/5 wt%TiB2 composite (a) and corresponding SADP (b).
630
Y. Zhang et al. / Materials and Design 28 (2007) 628–632 1000
ο
Intensity
800
ο TiB2
600
ο 400
ο
ο
200
ο
ο 10
20
30
40
50
60
70
ο
80
ο 90
2θ (degree)
Fig. 2. XRD pattern of in situ TiB2 particulates.
Fig. 3. Morphologies of in situ TiB2 particulates.
e ¼ DaDT ;
0.03
Al/ 5wt.% TiB2 Purity Aluminum
Tan (φ)
ð3Þ
where Da is the difference between the CTEs of reinforcement and matrix and DT is the temperature change during solidification of MMCs. According to the Granato-Lu¨cke dislocation theory [17], material damping is related to dislocations by the following equations:
Al/ 8wt.% TiB2 0.02
Al/5 wt%TiB2 composite over the studied temperature range. Interestingly, the damping capacity of purity aluminum and Al/5 wt%TiB2 composite has no obvious difference when temperature less than 85 C. The tendency of damping capacity for the three materials has little increase with increasing temperature at first, and when above 85 C, is decidedly temperature-dependent. Zhang and co-workers [9–11] had reported the possible dominant damping mechanisms for particulate reinforced Al MMCs at low temperatures are matrix dislocation damping, intrinsic damping of reinforcing particulate, and particulate/matrix interface damping is likely to be responsible at high temperatures. TiB2 reinforced Al MMCs differ from Gr particulate reinforced Al composites [9,12], in which intrinsic damping mechanism may be ruled out, because TiB2 particulates have lower damping capacity and were impossible to be deformed to dissipate vibration energy. Thus at relatively low temperature the damping capacity of Al/ TiB2 composite has related to dislocation damping. Vogelsang and Arsenault [13–15] had reported that a well-defined dislocation network in the vicinity of the reinforcement/matrix interface may be occurred in particulates reinforced MMCs. The origin of these dislocations is generally attributed to the difference in the coefficient of thermal expansion mismatch (CTE) of the metal matrix and that of the reinforcements. The CTE for TiB2 is 7.2 (in units of 106 C1), whereas a value of 24 is generally reported for aluminum. It is expected that such a large difference in CTE between matrices and reinforcements could generate a high density of dislocations during solidification of the MMCs. Consequently, these become a possible source of high damping capacity because of the motion of the dislocation under cyclic stress. The residual strain, or strain accumulation, produced as a result of the thermal mismatch, may be calculated from [16]
Q1 ¼ ðC 1 =e0 Þ expðC 2 =e0 Þ;
ð4Þ
0.01
0.00 50
100
150
200
Temp (°C)
Fig. 4. Damping capacity spectrum as a function of temperature for purity aluminum, Al/5 wt%TiB2 composite, Al/8 wt%TiB2 composite with testing frequency of 1 Hz.
where e0 is the strain amplitude, C1 and C2 are material constants and C1 is proportional to dislocation density in matrix. Eq. (4) shows that damping capacity is proportional to dislocation density. The contribution of dislocations to damping may be expected to fall with increasing temperature, as their concentration is decreased [14]. From materials point of view, introduce TiB2 particulates into Al matrix can cause dislocation density
Y. Zhang et al. / Materials and Design 28 (2007) 628–632
increasing, subsequently result in improvement in damping capacity. But Fig. 4 shows damping capacity of Al/ 5 wt%TiB2 composite and purity aluminum has the same level at relatively low temperature. The reason maybe there is not enough dislocation in matrix to cause improvement in damping capacity. With content of TiB2 increasing, the dislocation density is increasing. According to Eq. (4), the more dislocations in materials, the better damping capacity is. To some extent Al/ 8 wt%TiB2 composite with higher damping capacity may explain this very well. Also Fig. 4 indicates that at high temperature damping of MMCs are much higher than that of purity aluminum. As mentioned above, interface plays dominant role on improvement of damping capacity. At present study micron TiB2 particulates give rise to much more interface to MMCs than macro particulate reinforced MMCs. For further studying the effect of TiB2/matrix interface, damping capacity of Al/5 wt%TiB2 composite with 0.1 wt% Ti excess was obtained, as shown in Fig. 5. The idea of studying excess Ti stems from grain refinement of aluminum and aluminum alloy. In Al–Ti–B master alloy, there is some evidence that the TiB2 particulates can nucleate Al3Ti (which then nucleates a-Al) and a thin layer of Al3Ti coats the boride when sufficient excess Ti is present [18]. It is found that there is an orientation relationship between the aluminide and the boride [19]: f1 1 2gAl3 Ti kf0 0 0 1gTiB2 and h1 1 2 0iTiB2 kh2 0 1iAl3 Ti or h1 1 0iAl3 Ti . And orientation relationship between aluminum and Al3Ti is f1 1 1ga-Al kf1 1 2gAl3 Ti and h1 1 0ia-Al kh2 0 1iAl3 Ti or h1 1 0iAl3 Ti . The most important role of excess Ti in the melt is that it permits the formation of a thin layer of Al3Ti on the boride particles. As the Ti content is increased to take the overall composition of the melt into the two phase region in the phase diagram, the Al3Ti layers
0.03
Tan (φ)
0.02
Al/ 5wt.% TiB2 Al/ 5wt.% TiB2 with Ti excess
0.01
0.00
50
100
150 15
200
Temp (°C) Fig. 5. Comparison of damping capacity between Al/5 wt%TiB2 composite and Al/5 wt%TiB2 composite with Ti excess.
631
thicken to form particles [19]. In this case, excess Ti will play another role other than as a thin layer of Al3Ti. It can be seen from Fig. 5 that at low temperature Al/ 5 wt%TiB2 composite has higher damping capacity than that of composite with Ti excess and at relatively high temperature, on the contrary, damping of composite with Ti excess is higher than that of Al/5 wt%TiB2 composite. These may be due to at low temperature solution atoms, such as Ti, pin dislocation line so as to decline the length of dislocation line participated bowed movement during dissipate vibration energy and then result in decreasing in damping capacity. At high temperature appropriate excess Ti formed thin layer of Al3Ti on TiB2 particulates plays dominant role on improving damping capacity. Just as Tam and Tjong [20] reported line defects give rise to damping level in the intermediate to high range and surface defects in the high range.
4. Conclusion Introduced in situ TiB2 particulates into aluminum can cause improvement in damping capacity at relatively low temperature on condition that TiB2 content is more enough to produce large amounts of dislocations contributed to damping capacity increasing. Appropriate excess Ti in Al/TiB2 composite can improve damping capacity at relatively high temperature for it forms a thin layer of Al3Ti on TiB2 particulate and decrease damping capacity at low temperature for Ti atoms pin and limit dislocation line movement during dissipate vibration energy.
References [1] Gotman I, Koczak MJ, Shtessel E. Fabrication of Al matrix in situ composites via self-propagating synthesis. Mater Sci Eng A 1994;187:189–99. [2] Brinkman HJ, Duszczyk J, Katgerman L. In-situ formation of TiB2 in a P/M aluminum matrix. Scr Mater 1997;37:293–7. [3] Lloyd DJ. Particle reinforced aluminium and magnesium matrix composites. Int Mater Rev 1994;39:1–23. [4] Ma ZY, Tjong SC. High temperature creep behavior of in situ TiB2 particulate reinforced copper-based composite. Mater Sci Eng A 2000;284:70–6. [5] Biselli C, Morris D, Randall G. Mechanical alloying of highstrength copper alloys containing TiB2 and Al2O3 dispersoid particles. Scr Metall Mater 1994;30:1327–32. [6] Lu¨ L, Lai MO, Su Y, Teo HL, Feng CF. In situ TiB2 reinforced Al alloy composites. Scr Mater 2001;45:1017–23. [7] Smith AV, Chung DDL. Titanium diboride particle-reinforced aluminum with high wear resistance. J Mater Sci 1996;31:5961–73. [8] Viswanadham RK, Mannan SK, Kumar KS, Wolfenden A. Elastic modulus of NiAl TiB2 composites in the temperature range 300 to 1273 K. J Mater Sci Lett 1989;8:409–10. [9] Zhang J, Perez R, Lavernia J. Damping behavior of particulate reinforced 2519 Al metal matrix composites. Scr Metall Mater 1993;28:91–6.
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[10] Zhang J, Perez RJ, Lavernia EJ. Documentation of damping capacity of metallic, ceramic and metal-matrix composite materials. J Mater Sci 1993;28:2395–404. [11] Zhang J, Perez RJ, Lavernia EJ. Effect of SiC and graphite particulates on the damping behavior of metal matrix composites. Acta Metall Mater 1994;42:395–409. [12] Wei JN, Cheng HF, Zhang YF, Han FS, Zhou ZC, Shui JP. Effects of macroscopic graphite particulates on the damping behavior of commercially pure aluminum. Mater Sci Eng A 2002;325:444–53. [13] Vogelsang M, Arsenault R, Fisher J. In situ HVEM study of dislocation generation at Al/SiC interfaces in metal matrix composites. Metall Trans A 1986;17:379–89. [14] Arsenault R, Shi J. Dislocation generation due to differences between the coefficients of thermal expansion. Mater Sci Eng A 1986;81:175–87.
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