Key Engineering Materials Vol. 403 (2009) pp 251-252 online at http://www.scientific.net © (2009) Trans Tech Publications, Switzerland Online available since 2008/Dec/15
Pressureless Melt Infiltrated Non-Oxide Ceramic-Metal Composites A. Kalemtasa, G. Arslanb and F. Karac Department of Materials Science & Engineering, Anadolu University, Eskisehir, TURKEY a
[email protected],
[email protected],
[email protected]
Keywords: SiC, B4C, Al4C3, Si3N4, pressurless infiltration
Abstract. In the present study highly dense (open porosity < 1 %), light-weight (d ≤ 2.85 g/cm3) and Al4C3-free non-oxide ceramic-metal composites were produced at comparatively low temperatures (≤ 1250°C) by pressurless melt infiltration. Phase analysis of the SiC-B4C-Al composites revealed that a significant amount of hygroscopic Al4SiC4 and Al4C3 phases were formed. Si3N4 powder was added in different amounts to the SiC-B4C powder batches to suppress formation of these phases via in-situ reactions during the infiltration process. X-ray diffraction results of the SiC-B4C-Si3N4-Al composites confirmed that the incorporation of Si3N4 to the SiCB4C system reduced or eliminated the formation of the hygroscopic phases and resulted in in-situ formation of AlN, SiC and Si phases in the composite. Introduction SiC-Al system is one of the most promising candidates which satisfies the needs in many structural applications. Presence of significant amount of residual porosity and formation of undesired reaction products are the two well known problems of this system [1-3]. At temperatures above the melting point of Al, and under atmospheric pressure conditions, SiC becomes thermodynamically unstable and therefore have a driving force to dissolve in the Al matrix; because useful Al alloys contain elements that have a high affinity for Si and/or C, interfacial reactions may occur and result in reaction products such as Al4C3 and Al4SiC4. Furthermore, the reaction products themselves are thermodynamically unstable and have a tendency to hydrolyse with atmospheric moisture to form Al-hydroxide. The ∆G values of the above mentioned reactions obtained from MTDATA are given below. 4Al + 3C → Al4C3 Al4C3 + 12H2O → 3CH4 + 4Al(OH)3
∆G1200°C = (-)115.0 kj/mol ∆G25°C = (-)1693 kj/mol
(1) (2)
In this study it was aimed to produce fully dense SiC-B4C-Al composites devoid of Al4C3 by the help of the reactions between Si3N4, Al and Al4C3 given as follows: 4Al + Si3N4 → 4AlN + 3Si Al4C3 + Si3N4 → 4AlN + 3SiC
∆G1200°C = (-)355.0 kj/mol ∆G1200°C = (-)419.6 kj/mol
(3) (4)
Experimental Procedure Designed powder composition mixtures (Alfa Aesar SiC powder, H.C. Starck B4C Grade HS powder and Ube E-10 Si3N4 powder) given in Table 1 were planetary ball-milled (Pulverisette, P5 Model) for 1 h in alcohol and subsequently dried in a rotary evaporator (Heidolph WB2000, Germany). Pressureless melt infiltration of 2024 Al alloy into the porous ceramic preforms, prepared by uniaxial pressing, was performed under a flowing Ar gas atmosphere. Infiltration temperature and holding time was determined as 1200°&1250°C and 30 min, respectively. Bulk density measurements of the composites were carried out according to the Archimedes principle. Phase analysis of the powdered samples was determined by XRD (Rigaku Rint 2200, Japan) and All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 193.140.187.80-15/12/08,16:19:02)
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SiAlONs and Non-oxides
microstructural analyses of the polished and gold coated samples were carried out with SEM (ZEISS SUPRA 50 VP, Germany). Table 1. Compositions of prepared powder batches 50S50B 60S40B 70S30B 40S40B20S" SiC, wt. % 50 60 70 40 B4C, wt. % 50 40 30 40 Si3N4, wt. % ------20
35S35B30S" 35 35 30
30S30B40S" 30 30 40
Results Highly dense (open porosity < 1 %) and light-weight (ρ ≤ 2.85 g/cm3) ceramic-metal composites were produced. XRD analyses of SiC-B4C-Al composites confirmed the formation of Al4SiC4 and Al4C3 phases in significant amounts. Formation of these phases was suppressed significantly by the addition of Si3N4 powder to the compositions (Fig. 1). Reactions (3) and (4), thermodynamically favoured at even 1200°C, resulted in the depletion of the hygroscopic reaction products.
Relative intensity
: AlN : B4C : Al : Al3BC
: Al4C3 : Si : SiC : Al4SiC4
30S30B40SN
35S35B30SN
40S40B20SN
25
30
35
40
45
50
2θ θ Figure 1. XRD patterns of SiC-B4C-AlN-Si-Al composites produced at 1250°C SEM investigations confirmed the low porosity content and the homogeneous distribution of B4C powders in the produced composites. Conclusions Highly dense and light-weight non-oxide ceramic-metal composites were produced by pressureless melt infiltration. Infiltration of SiC-B4C with Al causes the formation of Al4SiC4 & Al4C3 phases and addition of Si3N4 powder to the composition prevents their formation. Acknowledgement The authors would like to thank Anadolu University Scientific Research Council for the financial support of this work through the project 030235. References [1] T. Iseki, T. Kameda, T. Maruyama: J. Mater. Sci. 19 (1984), p. 1692 [2] V. Laurent, D. Chatain, N. Eustathopoulos: J. Mater. Sci. 22 (1987), p. 244 [3] D.J. Lloyd, H. Lagage, A. McLeod, P.L. Morris: Mater. Sci. Eng. A107 (1989), p. 73
Key Engineering Materials Vol. 403
SiAlONs and Non-oxides doi:10.4028/0-87849-345-X Pressureless Melt Infiltrated Non-Oxide Ceramic-Metal Composites doi:10.4028/0-87849-345-X.251
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