A

scta3tib©

K

1

aoptii

fm[ootm

t

0d

Materials Science and Engineering A 473 (2008) 254–258

Effect of SiC coating and heat treatment on damping behaviorof C/SiC composites

Qing Zhang, Laifei Cheng ∗, Wei Wang, Litong Zhang, Yongdong XuNational Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi’an 710072, China

Received 30 October 2006; received in revised form 19 March 2007; accepted 19 June 2007

bstract

Three groups of 2D and 3D C/SiC composites were fabricated by chemical vapor infiltration (CVI) process: the first group was as received, theecond group was treated at 1500 ◦C in vacuum atmosphere for 2 h, and the third group was deposited with a chemical-vapor-deposited (CVD) SiCoating. Damping properties of these composites were measured by dynamical mechanical analyzer (DMA) at different frequencies from roomemperature to 400 ◦C in air atmosphere. The results show that SiC coating and heat treatment decrease damping capacity of C/SiC compositesnd the damping peak disappears or decreases in the testing temperature range. The effect of CVD SiC coating on damping behavior of 2D andD C/SiC composites is mainly related to the change of porosity and is independent of fiber preform architecture. However, the effect of heat

reatment on damping behavior of 2D and 3D C/SiC composites is mainly attributed to the change in the SiC matrix and interphase bonding, andt is dependent on fiber preform architecture. Both of CVD SiC coating and heat treatment studied in this paper have no influence on relationshipetween damping behavior of C/SiC composites and frequency. 2007 Elsevier B.V. All rights reserved.

pertie

hiSco

2

2

(dfrb

eywords: Carbon fiber composites; Chemical vapor infiltration; Damping pro

. Introduction

Carbon fiber reinforced silicon carbide (C/SiC) compositesre considered to be the most potential candidates in the fieldsf aeronautics and astronautics due to low density and gooderformance at high temperatures [1,2]. They are widely usedo fabricate items such as nozzles, tubes, plates, and shells. Its well recognized that the performance of these applications isnfluenced by the change of microstructure of the materials.

The damping capacity, Q−1, is an important means not onlyor evaluating the performance of materials in vibration environ-ent, but also for investigating the evolution of microstructure

3–7], for instance, diffusion of elements, defects and cracksf matrix materials, debonding and sliding at interphase and son. However, there were few reports on the damping proper-ies of ceramic matrix composites, especially C/SiC composite

aterials.CVD SiC coating and heat treatment (HT) are important

echnics to improve the properties of the materials, and they

∗ Corresponding author. Tel.: +86 29 8849 4616; fax: +86 29 8849 4620.E-mail address: chenglf@nwpu.edu.cn (L. Cheng).

tilwAt1

921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.msea.2007.06.049

s

ave certain effects on microstructure of C/SiC composites. Its the purpose of this paper to investigate the effects of CVDiC coating and heat treatment on damping behavior of C/SiComposites. The damping mechanisms related to the evolutionf microstructure have been discussed, too.

. Experimental

.1. Materials procedure

Two kinds of fiber preforms were prepared: two-dimensional2D) by laminating 1K T-300 woven carbon fabrics and three-imensional (3D) by braiding 3K T-300 carbon fibers inour-step method. The volume of fibers was controlled in theange from 40 to 45%. The preforms were infiltrated withoth pyrolysis carbon (PyC) as interphase and SiC as matrixo fabricate C/SiC composites by low-pressure chemical vapornfiltration (LPCVI) method using butane and methyltrichlorosi-ane (MTS) [8]. The infiltration conditions of PyC interlayer

ere as follows: temperature 960 ◦C, pressure 5 KPa, time 20 h,r flow 200 ml min−1, butane flow 15 ml min−1. The infiltra-

ion conditions of SiC matrix were as follows: temperature000 ◦C, pressure 5 KPa, time 120 h, H2 flow 350 ml min−1,

and Engineering A 473 (2008) 254–258 255

A1moTg1dc

2

Umtdott

3

3

aicCwppclsd

Fa(

Fm

kSipoatt2oimi

Q. Zhang et al. / Materials Science

r flow 350 ml min−1, and the molar ratio of H2 and MTS0. The porosity of the composites was about 16%. Speci-ens were machined from the fabricated composite in the size

f 3 mm × 12 mm × 50 mm without further deposition of SiC.hen, the specimens were divided into three groups: the firstroup was just as received, and the second group was treated at500 ◦C in vacuum atmosphere for 2 h, and the third group waseposited with a 20 �m-thick CVD SiC coating under the sameonditions as SiC matrix.

.2. Measurement procedure

Dynamical mechanical analyzer made by TA Company ofSA was employed for measurements of the dynamic storageodulus (E′) and loss modulus (E′′) with increasing tempera-

ure and forced vibrations by three-point bending method. Theamping capacity, Q−1, can be expressed as: Q−1 = E′/E′′. Allf measurements were carried out in air atmosphere from roomemperature to 400 ◦C, the vibration amplitude being 2 �m andhe testing frequency 1, 2, 5, and 10 Hz, respectively.

. Results and discussion

.1. Damping behavior of 2D and 3D C/SiC composites

The dependence of damping capacity Q−1 on temperaturend frequency for the as-received 2D and 3D C/SiC compos-tes is shown in Fig. 1. It is clearly shown that the dampingapacity changed as a function of the temperature for both of/SiC composites. The damping capacity increased graduallyith increasing temperature and then decreased after dampingeak appeared in the temperature range of 250–300 ◦C. Com-ared with 2D C/SiC composites, damping peaks for 3D C/SiC

omposites were lower at equal frequency. It resulted from inter-ayer friction proper to 2D C/SiC composites under an alternatetress due to its laminated structure. This could be confirmed byelamination of tested 2D C/SiC composites.

ig. 1. Temperature dependence of damping capacity for the as-received 2Dnd 3D C/SiC composites: (rhombus) 1 Hz, (square) 2 Hz, (triangle) 5 Hz, andcircle) 10 Hz. Open (closed) symbols indicate 3D (2D) C/SiC composites.

ortc

i(

Q

wpdtr

3a

fSca

ig. 2. Debonding occurred at the boundary between PyC interphase and SiCatrix.

Cooling from manufacture temperature to room temperature,inds of defects, such as dislocation [9] and microcracks iniC matrix, distortion in PyC interphase, debonding between

nterphase and matrix and so on, would be produced in the com-osites because of thermal stress induced by thermal mismatchf three different components. After the forced vibration waspplied, the dislocation vibrated around its equilibrium posi-ion and the mobility of dislocation gradually increased with theemperature increasing, then the damping capacity grew before50 ◦C. The damping peak appeared in the temperature rangef 250–300 ◦C induced by interfacial friction at the debond-ng region between interphase and matrix (Fig. 2) and possibly

icrocracks expanding in SiC matrix [10]. As the temperaturencreasing, the damping capacity decreased due to the decrementf interstices in the composites caused by thermal expansion andesidual stress releasing gradually. The oxidation effect was notaken into account because no oxidation was observed after theomposites were tested.

As Parrini and Schaller [11] reported, the damping capac-ty Q−1 is in inverse proportion to the vibration frequencyf):

−1 = const (dT/dt)

f(1)

here dT/dt is the rate of temperature change. For C/SiC com-osite studied in this work, damping capacity and peak valuesecreased gradually with the increasing testing frequency andhe damping peak shifted to the lower temperatures. The similaresults were reported in Refs. [12,13].

.2. The effect of SiC coating on damping behavior of 2Dnd 3D C/SiC composites

The dependence of damping capacity on temperature and

requency for 2D C/SiC composites with and without CVDiC coating is shown in Fig. 3. It can be seen that CVD SiCoating decreases damping capacity for 2D C/SiC compositesnd makes damping peak disappear. The damping capacity of

256 Q. Zhang et al. / Materials Science an

Fig. 3. Variations of damping capacity with temperature and frequency for 2DC1c

Sw

tadd3ctic

Sp

FC1c

crdTbdafdcWrpaicbdp

32

ahditvat

/SiC composites: (rhombus) 1 Hz, (square) 2 Hz, (triangle) 5 Hz, and (circle)0 Hz. Open (closed) symbols indicate 2D C/SiC composites without (with) SiCoating.

iC-coated 2D C/SiC composites increases monotonously in thehole testing temperature range.Fig. 4 illustrates the dependence of damping capacity on

emperature and frequency for 3D C/SiC composites withnd without CVD SiC coating. Similarly, CVD SiC coatingecreases damping capacity for 3D C/SiC composites and makesamping peak disappear. The damping capacity for SiC-coatedD C/SiC composites changes in a similar way like that of SiC-oated 2D C/SiC composites, i.e. increasing monotonously inhe whole testing temperature range. With the testing frequencyncreasing, the damping capacity for all of 2D and 3D C/SiComposites decreases gradually.

The data indicate that for 2D and 3D C/SiC composites, CVDiC coating decreases damping capacity and makes dampingeak disappear. It is considered that the influence of CVD SiC

ig. 4. Variations of damping capacity with temperature and frequency for 3D/SiC composites: (rhombus) 1 Hz, (square) 2 Hz, (triangle) 5 Hz, and (circle)0 Hz. Open (closed) symbols indicate 3D C/SiC composites without (with) SiCoating.

tWo

ahtCtpatpi

dagsn

ob

d Engineering A 473 (2008) 254–258

oating on damping capacity of C/SiC composites is mainlyelated to the change of porosity.1 It can be confirmed by theecreasing porosity from 16% before coated to 13% after coated.here were plenty of open pores at the surface of specimensefore a SiC coating deposited, as shown in Fig. 5(a). During theepositing process, these open pores were filled with SiC grainsnd then the coating was formed, as shown in Fig. 5(b). There-ore, the porosity would decrease after the composites wereeposited with a SiC coating. This implies that pores in C/SiComposites play an important role in their damping capacity. Asang et al. [6] researched, porosity damping of carbon-fiber-

einforced porous composites is approximately proportional toorosity. The elastic energy is dissipated through the dilatationalnd distortional energy of pores. Therefore, the damping capac-ty decreases with decreasing porosity. Furthermore, CVD SiCoating has no influence on the relationship between dampingehavior and frequency, and the effect of CVD SiC coating onamping behavior of C/SiC composites is independent of fiberreform architecture.

.3. The effect of heat treatment on damping behavior ofD and 3D C/SiC composites

Fig. 6 shows the variations of damping capacity with temper-ture and frequency for 2D C/SiC composites with and withouteat treatment. It can be seen that heat treatment decreasesamping capacity and peak values for 2D C/SiC compos-tes and changes the shift of damping peak in direction. Ashe testing frequency increasing, damping capacity and peakalue for as-received 2D C/SiC composites decreases graduallyccompanied with a shift of damping peak towards the loweremperatures, while for heat-treated 2D C/SiC composites theemperature of damping peak shifts to the higher temperatures.

ith the testing frequency increasing, damping capacity for bothf the 2D C/SiC composites decreases gradually.

Fig. 7 shows the dependence of damping capacity on temper-ture and frequency for 3D C/SiC composites with and withouteat treatment. It is similar to 2D C/SiC composites that heatreatment decreases damping capacity and peak values for 3D/SiC composites except at 1 Hz, while it does not change

he shift of damping peak in direction. Damping capacity andeak value for both 3D C/SiC composites decreases graduallyccompanied with a shift of damping peak towards the loweremperatures with the testing frequency increasing. Dampingeak for heat-treated 3D C/SiC composites at 1 Hz slightlyncreases.

The data indicate that heat treatment generally decreasesamping capacity for 2D and 3D C/SiC composites. It can be

ttributed to the change in SiC matrix. Tiny SiC grains wereenerated in CVI process with great internal stress and many oftructural defects, such as dislocation. The relaxation of inter-al stress and the mobility of dislocation became the source of

1 The porosity in this paper means open porosity, which was measured basedn the Archimedes method. The closed porosity was not taken into accountecause it never changed after the specimens were coated.

Q. Zhang et al. / Materials Science and Engineering A 473 (2008) 254–258 257

Fig. 5. The appearance of C/SiC composites: (a) before coated and (b) after coated.

Fig. 6. Variations of damping capacity with temperature and frequency for 2DC/SiC composites: (rhombus) 1 Hz, (square) 2 Hz, (triangle) 5 Hz, and (circle)1S

Fig. 7. Variations of damping capacity with temperature and frequency for 3DC/SiC composites: (rhombus) 1 Hz, (square) 2 Hz, (triangle) 5 Hz, and (circle)

0 Hz. Open (closed) symbols indicate 2D C/SiC composites untreated (treated)iC coating.

1S

Fig. 8. SEM photographs of polished 3DC/SiC composites:

0 Hz. Open (closed) symbols indicate 3D C/SiC composites untreated (treated)iC coating.

(a) without heat treatment and (b) with heat treatment.

2 ce an

eihtidiatPttroditivfMdwat

4

imctirtptfa

ptb

A

eYfv

R

[[[

[[

[

[

58 Q. Zhang et al. / Materials Scien

nergy dissipation in vibration environment, and the compos-tes showed high damping capacity. However, the stabilizingeat treatment at 1500 ◦C results in the release of internal stress,he annealing of defects and grain growth [14]. Then, the damp-ng capacity decreases due to the source of energy dissipationecreasing. On the other hand, heat treatment can decreasenterphase bonding strength and enlarge the debonding of fibernd matrix [15,16]. For the as-received C/SiC composites, tex-ured graphitoid areas were observed by Li [17] at the edge ofyC interphase near by the fibers, and the other part was in

urbostratic stacking structure. During the processing of heatreatment, sliding occurred in the textured graphitoid areas toelease the thermal stresses induced by the thermal mismatchf fibers and PyC, and then interphase bonding strength wasecreased [18]. Moreover, as shown in Fig. 8, the debond-ng areas were enlarged after heat treatment because of thehermal mismatch of fiber and matrix. Therefore, friction innterphase area is enhanced and can dissipate much energy inibration, which is considered as the reason why damping peakor heat-treated 3D C/SiC composites at 1 Hz slightly increases.

oreover, heat treatment has different effects on the shift ofamping peak in direction for 2D and 3D C/SiC composites,hich is conceived that it is related to different fiber preform

rchitectures. Furthermore, heat treatment has no influence onhe relationship between damping behavior and frequency.

. Conclusions

The effects of CVD SiC coating and heat treatment on damp-ng behavior of 2D and 3D C/SiC composites and the relatedechanisms have been investigated. Damping capacity of SiC-

oated and heat-treated C/SiC composites are mostly lower thanhat of as-received C/SiC composites. The reduction in the damp-ng capacity of 2D and 3D SiC-coated C/SiC composites mainlyesults from the decrease of porosity. However, the decrease ofhe damping capacity of 2D and 3D heat-treated C/SiC com-

osites is mainly attributed to the change of microstructure inhe SiC matrix and interphase bonding. Heat treatment has dif-erent effects on the shift of damping peak in direction for 2Dnd 3D C/SiC composites, which is related to different fiber

[

[

d Engineering A 473 (2008) 254–258

reform architectures. Both of CVD SiC coating and heatreatment have no influence on relationship between dampingehavior of C/SiC composites and frequency.

cknowledgements

The authors acknowledge the financial support of Natural Sci-nce Foundation of China (Contract No. 90405015), Nationaloung Elitists Foundation (Contract No. 50425208), Program

or Changjiang Scholars and Innovative Research Team in Uni-ersity.

eferences

[1] J.F. Jamet, P. Lamicq, in: R. Naslain, J. Lamon, D. Doumeingts (Eds.),High Temperature Ceramic Matrix Composites I, HT-CMC I, WoodheadPublishing Limited, Cambridge, England, 1993, pp. 735–742.

[2] S. Jacques, A. Guette, F. Langlais, R. Naslain, S. GouJard, J. Eur. Ceram.Soc. 17 (1997) 1083–1092.

[3] K. Nishiyama, M. Yamanaka, M. Omori, S. Umekawa, J. Mater. Sci. Lett.9 (1990) 526–528.

[4] R. Chandra, S.P. Singh, K. Gupta, Compos. Struct. 46 (1999) 41–51.[5] W.Z. Li, P.Q. Zhang, J.H. Ruan, J. China Univ. Sci. Technol. 4 (2000)

393–400.[6] C. Wang, Z.G. Zhu, X.H. Hou, H.J. Li, Carbon 38 (2000) 1821–1824.[7] S. Sato, H. Serizawa, T. Noda, A. Kohyama, J. Alloys Compd. 355 (2003)

142–147.[8] L.F. Cheng, Y.D. Xu, Q. Zhang, L.T. Zhang, Carbon 41 (2003) 707–711.[9] X.Y. Yang, Ph.D. Thesis, Institute of Metal Research, Chinese Academy

of Science, Shenyang, China, 2000.10] V. Birman, L.W. Byrd, Int. J. Solids Struct. 40 (2003) 4239–4256.11] L. Parrini, R. Schaller, Scripta Metall. Mater. 28 (1993) 763–767.12] X. Zhang, R. Wu, X. Li, Z.X. Guo, Sci. China E 32 (2002) 14–19 (in

Chinese).13] L. Parrini, R. Schaller, Acta Mater. 44 (1996) 4881–4888.14] Y.D. Xu, L.T. Zhang, L.F. Cheng, Acta Aeronaut. Astronaut. Sin. 18 (1997)

123–126.15] H. Kodama, H. Sakamoto, T. Miyoshi, J. Am. Ceram. Soc. 72 (1989)

551–558.16] F. Lamouroux, G. Camus, J. Thebault, J. Am. Ceram. Soc. 77 (1994)

2049–2057.17] J.Z. Li, Ph.D. Thesis, Northwestern Polytechnical University, Xian, China,

2007.18] Y.J. Ye, M.S. Thesis, Northwestern Polytechnical University, Xian, China,

2003.