Liquid metal infiltration into ceramic particle compacts chemically and morphologically heterogeneous

Materials Science and Engineering A 495 (2008) 288–291

Liquid metal infiltration into ceramic particle compacts chemically and morphologically heterogeneous E. Pi˜nero a,b , J.M. Molina b,c,∗ , J. Narciso b,d , E. Louis a,b,e a

Departamento de F´ısica Aplicada, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain c Laboratory of Mechanical Metallurgy, Institute of Materials, Ecole ´ Polytechnique F´ed´erale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland d Departamento de Qu´ımica Inorg´ anica, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain e Unidad Asociada del Consejo Superior de Investigaciones Cient´ıficas, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain b

Received 21 March 2007; received in revised form 8 November 2007; accepted 21 November 2007

Abstract The threshold pressure P0 for infiltration of Al–12 wt.% Si alloy into compacts of mixtures of alumina and silicon carbide particles having largely different size is investigated. The results are in line with those recently derived from infiltrations of Al into bimodal SiC compacts, namely, P0 remains almost constant for fractions of coarse particles below that which gives the maximum particle volume fraction, decreasing there onwards down to the value corresponding to coarse particles. The experimental data for P0 can be reasonably fitted by generalizing an approach, recently developed for SiC bimodal compacts, which gives P0 in terms of the mixture specific surface area calculated by means of the linear rule of mixtures. © 2008 Elsevier B.V. All rights reserved. Keywords: Metal matrix composites; Bimodal particle mixtures; Pressure infiltration

1. Introduction Decreasing the size of microelectronic devices requires the development of supporting materials having a low thermal expansion coefficient, not too far from that of silicon, and a high thermal conductivity to help extracting the high amount of heat produced in these systems [1–5]. One of the material families that are being tested is that of metal–matrix composites (MMCs) with volume percentages of reinforcement higher than 60%. Such high compactness can only be obtained by either using continuous preforms or particle preforms having bimodal or multimodal size distributions. On the other hand, an efficient fabrication route to produce the composites is gas pressure infiltration. Although the technology being utilized by the industry since several years is reasonably developed, there are very few published fundamental studies of the key aspects of the infiltration process [6–10]. Recently, the present authors published a study of the infiltration of pure aluminum into bimodal mixtures

∗ Corresponding author at: Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain. Tel.: +34 965903400 2055; fax: +34 965909726. E-mail address: [email protected] (J.M. Molina).

0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.11.089

of SiC particles of two largely different sizes [7]. Conclusive experimental evidence was presented which indicated that the threshold pressure for infiltration P0 remained constant up to the fraction of coarse particles that produced the maximum volume fraction of reinforcement. There onwards, P0 decreased down to the value corresponding to compacts containing only coarse particles. On the other hand, calculating the specific surface area of the mixture by means of the linear mixture rule allowed fitting those experimental results [9,10]. The purpose of this work is to investigate the infiltration of liquid metals into ceramic compacts being chemically and morphologically heterogeneous. Such study is not only interesting from a fundamental point of view, but it also has a significant technological relevance as the use of mixtures of different reinforcements is being recently evaluated for a variety of applications [11,12]. Experimental data for the threshold pressure for infiltration of the Al–12 wt.% Si alloy into compacts of bimodal mixtures of alumina and SiC particles having largely different size will be presented and discussed. The results for the threshold pressure versus the fraction of coarse particles show a similar trend to those mentioned above for infiltration of aluminum into SiC compacts. In addition, a general method that allows fitting (and, in some cases, predicting) the results for the threshold pressure in these systems is herewith proposed.

E. Pi˜nero et al. / Materials Science and Engineering A 495 (2008) 288–291

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Table 1 Main characteristics of the SiC and Al2 O3 particles used in this work Type

D

D(90)

D(10)

Span

SBET

SiC-100 SiC-500 Al2 O3 -F120 Al2 O3 -AA10

167 16.7 145 12.0

229 24.1 204 15.5

110 10.4 92 9.1

0.71 0.82 0.79 0.56

82 360 80 490

D (␮m) is the average diameter of the particles. D(x) is the diameter below which x% of the particles are found. The span of the size distribution is defined as (D(90) − D(10))/D(50). SBET is the surface area (m2 /kg) measured by means of nitrogen adsorption.

2. Materials and experimental procedures The main characteristics of the SiC and Al2 O3 particles used in this work are given in Table 1. Particles are rounded with a low aspect ratio of approximately 2, except Al2 O3 -AA10 particles that have an aspect ratio of around 1.5, and densities of 3210 (SiC) and 3960 (alumina) kg/m3 . Commercially pure aluminum and silicon (purities of ∼99.98 wt.%) were used to prepare the Al–12 wt.% Si alloy. The alloy density and liquid–vapor surface tension, 2450 kg/m3 and 855 mN/m, respectively, were taken from Ref. [13]. Preparing the compacts of bimodal mixtures requires following the specific procedures described in Ref. [7]. Particles were thoroughly cleaned and mixed in ethanol. Once the mixtures were dried up, they were put into quartz tubes (5 mm of inner diameter) and packed by means of strokes of a weight. Special care has to be taken to avoid segregation (no vibrations were applied as they greatly favor segregation). Particle segregation may lead to preferential infiltration paths. The attained particle volume fraction versus the volume fraction of coarse particles xc are reported in Table 2. In preparing the mixtures it is easier to use mass fractions yi , the relation between the two magnitudes in a mixture of N particulates is, ⎞ ⎛ N  y j⎠ xi = ⎝ ρi yi (1) ρj j=1

where ρi is the density of particulate i. Once the transformation is done, the volume fractions have to be normalized, dividing each xi by the sum of all of them. Table 2 Particle volume fraction Vp and threshold pressure for infiltration P0 versus the fraction of coarse particles xc SiC-500/Al2 O3 -F120

Al2 O3 -AA10/SiC-100

xc

Vp

P0 (kPa)

xc

Vp

0 0.25 0.5 0.6 0.69 0.75 1

0.55 0.61 0.68 0.71 0.70 0.68 0.56

898 881 900 923 738 495 190

0 0.25 0.5 0.6 0.72 0.8 1

0.59 0.66 0.73 0.75 0.73 0.66 0.58

P0 (kPa) 972 1009 1024 1021 494 218 162

The results correspond to compacts of the two mixtures SiC-500/Al2 O3 -F120 and Al2 O3 -AA10/SiC-100 investigated in this work (see Table 1), infiltrated with alloy Al–12 wt.% Si at 898 K.

Fig. 1. Experimental data for the particle volume fraction Vp (inset) and threshold pressure for the infiltration P0 of the alloy Al–12 wt.% Si at 898 K into compacts of the mixture SiC-500/Al2 O3 -F120 (bimodal size distribution) versus the fraction of coarse particles xc (Al2 O3 -F120). The continuous line corresponds to results derived from Eq. (5) (see text).

The infiltration system used in this work was described in detail elsewhere [14,15]. Infiltration was carried out at 898 K. No inert atmosphere was introduced into the packed powder. An alumina paper of low density was placed at the compact ends to avoid depacking and to skim off the oxide layer that initially covers the metal surface. The quartz tube containing the packed powder was attached at the top of the pressure chamber and preheated by holding the quartz tube just above the melt for no more than 80 s. Just before immersion, the metal surface was thoroughly cleaned. The chamber was closed and pressure was raised (introducing nitrogen gas) up to the chosen pressure. After 120 s at pressure, the chamber was vented, the sample taken out of the melt, air-cooled and sectioned. The infiltration height was measured with a precision gauge. 3. Results The experimental results for the particle volume fraction Vp versus the fraction of coarse particles xc are reported in Table 2 and depicted in the insets of Figs. 1 and 2. As expected, Vp shows a maximum around xc = 0.65 for the two mixtures investigated here. The maximum particle volume fraction is higher in Al2 O3 AA10/SiC-100 than in SiC-500/Al2 O3 -F120 mixture, 0.75 and 0.71, respectively (see Table 2). The experimental data can be nicely fitted by means of the model proposed by Yu and Standish [16] (solid lines in the insets of Figs. 1 and 2). The results for the threshold pressure P0 versus the fraction of coarse particles in the mixture are reported in Table 2 and shown in Figs. 1 and 2. The qualitative behavior in the two mixtures is very similar and does not differ from that reported in [7] for bimodal mixtures of SiC particles. Specifically, the threshold pressure for infiltration remains almost constant up to the value of xc which gives the maximum particle volume fraction. Thereafter, P0 decreases steadily down to the value corresponding to a compact containing only coarse particles. As pointed out in [7], the fact that the

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Fig. 2. Experimental data for the particle volume fraction Vp (inset) and threshold pressure for the infiltration P0 of the alloy Al–12 wt.% Si at 898 K into compacts of the mixture Al2 O3 -AA10/SiC-100 (bimodal size distribution) versus the fraction of coarse particles xc (SiC-100). The continuous line corresponds to results derived from Eq. (5) (see text).

threshold pressure varies only slightly in going from the small particle end up to the fraction of coarse particles that gives the maximum Vp can be understood by noting that the local compactness of small particles (which in this system determines P0 ) is almost unaffected by the addition of coarse particles. The latter was checked by means of optical microscopy [7,17] and is the basic assumption of a simple model successfully used [7,10,18] to predict the particle volume fraction in bimodal mixtures near the small particles end (not too large xc ). A procedure capable of predicting P0 in compacts made out of mixtures chemically and morphologically inhomogeneous is discussed in Section 4.

Fig. 3. Threshold pressure for infiltration P0 of pure aluminum at 973 K into mono-modal compacts of alumina (filled circles) or SiC particles (empty circles) versus the particle surface area per unit volume of metal matrix Σ i . The straight lines correspond to fittings (forced to pass through the origin) from which the contact angle can be derived (see text).

In this equation, γ lv is the liquid–vapor surface tension of the metal, and θ i the contact angle at the interface liquid metal/particle i. In turn, Σ i is written as Σi =

xi Vp ρi S i Vm

where xi is the volume fraction of particles i in the preform and ρi and Si are its density and specific surface area (m2 /kg), respectively. The total fraction of particles and that of metal, are denoted by Vp and Vm , respectively (note that Vm = 1 − Vp ). In the present case, as the preform has only two types of particles, fine f and coarse c, the Young–Dupr´e equation (also known as capillary law) reads as

4. Discussion The approach proposed in [9,10] for predicting the threshold pressure in bimodal mixtures cannot be applied to the present case. Having two types of particulate implies not only that the particle specific surface area is different (as in the bimodal compacts of the same ceramic particulate investigated in [9,10]) but also that the parameter characterizing the metal/ceramic interface (contact angle) varies. Thus, we hereby generalize that procedure along the following lines. The Young-Dupr´e equation [14], which gives the threshold pressure for infiltration of a liquid into a preform in terms of the work of immersion Wi of particle i into the metal and of the particle surface area per unit volume of metal matrix Σ i , is rewritten as P0 =

N 

W i Σi

(2)

i=1

where N is the number of different particulate in the preform. On the other hand, the work of immersion of particle i into the metal, is given by Wi = γlv cos θi

(3)

(4)

P0 = γlv

Vp [ρf Sf cos θf (1 − xc ) + ρc Sc cos θc xc ] 1 − Vp

(5)

This expression reduces to the one used in Ref. [9] to investigate the case of bimodal mixtures of SiC particles, taking ρc = ρf and θ c = θ f . Before proceeding to discuss how Eq. (5) was applied to the present case, and in order to support the crucial role of the particle surface area per unit volume of metal matrix Σ i , we present in Fig. 3 experimental data for P0 versus Σ i , derived from infiltrations of pure Al at 973 K into mono-modal compacts of alumina or SiC particles of size varying over a rather wide range. The results shown in the figure clearly indicate that P0 ∝ Σ i , as in Eq. (2). In addition, the contact angles derived from linear fittings of the data (also shown in Fig. 3) are very similar, namely, 114◦ and 121◦ for alumina and SiC, respectively (this amounts to a 20% difference in the cosines). As noted in [14], this weak dependence on the chemical nature of the compact is mainly a consequence of the oxide layer that covers liquid aluminum. In fitting the experimental results for the threshold pressure versus the fraction of coarse particles xc in bimodal mixtures of SiC, the authors of [9] used as parameters the contact angle and the specific surface area of coarse particles Sc . This procedure

E. Pi˜nero et al. / Materials Science and Engineering A 495 (2008) 288–291

was justified arguing that Sc was too low to be detected by actual experimental techniques. However, fittings led to values of Sc close to the experimental data. This result supports the procedure followed here in fitting the experimental data with Eq. (5): (i) take the experimental data for both Sf and Sc , and fit the contact angle to the P0 results for each of the four mono-modal compacts, and, (ii) calculate P0 versus xc by introducing the so fitted contact angles and the experimental data for the surface areas in Eq. (5). The contact angles derived from fittings to results for mono-modal preforms are: Al2 O3 -AA10, 114◦ , Al2 O3 -F120, 123◦ , SiC-100, 121◦ and SiC-500, 138◦ (a similar result for the latter particles was reported in Ref. [19]). As far as the contact angle is concerned these results are not very satisfactory, in the sense that they show a considerable dependence on the ceramic. The fact the surface areas were measured prior to packing may be the origin of this failure. Actually, particle breaking during packing may change the average surface area (solving this problem may require the measurement of the surface area of the compact itself). Figs. 1 and 2 depict the experimental data for P0 versus xc along with the results obtained by introducing the fitted contact angles and the data for the surface areas in Eq. (5). The agreement is satisfactory. The method suggested here provides a way for predicting the threshold pressure in systems for which surface areas and contact angles can be determined in advance. 5. Concluding remarks In this work, the applicability of the capillary law to compacts both morphologically and chemically inhomogeneous has been discussed. The analysis has been illustrated by means of experimental results for the threshold pressure for the infiltration of Al–12 wt.% Si eutectic alloy into compacts of bimodal mixtures of alumina and SiC particles. It turns out that a very satisfactory description of the experimental data can be obtained by writing the threshold pressure as a sum over the solid (ceramic) components of the product of the work of immersion and the particle surface area per unit volume of metal matrix. The approach can be used to predict the threshold pressure in systems for which

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the required information (contact angles, particle surface area, fraction of coarse particles, total fraction of reinforcement, etc.) is available. Acknowledgement Partial support from the Spanish “Ministerio de Educaci´on y Cultura” (grant MAT2004-03139), the Universidad de Alicante and the Generalitat Valenciana is gratefully acknowledged. References [1] R. Viswanath, V. Wakharkar, A. Watwe, V. Lebonheur, Intel. Technol. J. 4 (2000) 1–16. [2] M.A. Occhionero, Surf. Mount. Tech. 19 (2005) 32–37. [3] R. Irvin, Adv. Microelectr. 29 (2002) 9–11. [4] D. Chung, C. Zweben, in: A. Kelly, C. Zweben (Eds.), Comprehensive Composite Materials, vol. 6, Elsevier Science Ltd., 2000, pp. 701–724. [5] T.W. Clyne, in: A. Kelly, C. Zweben (Eds.), Comprehensive Composite Materials, vol. 3, Elsevier Science Ltd., 2000, pp. 447–468. [6] J.M. Molina, R. Saravanan, R. Arp´on, C. Garc´ıa-Cordovilla, E. Louis, J. Narciso, Trans. JWRI 30 (2001) 449–454. [7] J.M. Molina, R.A. Saravanan, R. Arp´on, C. Garc´ıa-Cordovilla, E. Louis, J. Narciso, Acta Mater. 50 (2002) 247–257. [8] R. Arp´on, J.M. Molina, R.A. Saravanan, C. Garc´ıa-Cordovilla, E. Louis, J. Narciso, Acta Mater. 51 (2003) 3145–3156. [9] J.M. Molina, R. Arp´on, R.A. Saravanan, C. Garc´ıa-Cordovilla, E. Louis, J. Narciso, Scripta Mater. 51 (2004) 623–627. [10] J.M. Molina, E. Pi˜nero, J. Narciso, C. Garc´ıa-Cordovilla, E. Louis, Curr. Opin. Solid State Mater. Sci. 9 (2005) 202–210. ¨ [11] H. Hildhack, G. Jelinek, Osterreichische Patentamt.(requested). [12] R. Prieto, J. Narciso, E. Louis, Patente Espa˜nola P002700804 (2007). [13] J. Goicoechea, C. Garcia-Cordovilla, E. Louis, A. Pamies, J. Mater. Sci. 27 (1992) 5247–5252. [14] C. Garc´ıa-Cordovilla, E. Louis, J. Narciso, Acta Mater. 47 (1999) 4461–4479. [15] A. Alonso, A. Pamies, J. Narciso, C. Garc´ıa-Cordovilla, E. Louis, Metall. Trans. A 24 (1993) 1423–1432. [16] A.B. Yu, N. Standish, Powder Technol. 55 (1988) 171–186. [17] J.M. Molina, PhD, Thesis, Universidad de Alicante, 2004. [18] R.M. German, Particle Packing Characteristics, Metal Powder Industrial Federation, Princenton, 1989. [19] J. Tian, E. Pi˜nero, J. Narciso, E. Louis, Scripta Mater. 53 (2005) 1483–1488.