Chemical vapor infiltration

Résumé

Chemical vapour infiltration (CVI) is a ceramic engineering process whereby matrix material is infiltrated into fibrous preforms by the use of reactive gases at elevated temperature to form fiber-reinforced composites. The earliest use of CVI was the infiltration of fibrous alumina with chromium carbide. CVI can be applied to the production of carbon-carbon composites and ceramic-matrix composites. A similar technique is chemical vapour deposition (CVD), the main difference being that the deposition of CVD is on hot bulk surfaces, while CVI deposition is on porous substrates. Process During chemical vapour infiltration, the fibrous preform is supported on a porous metallic plate through which a mixture of carrier gas along with matrix material is passed at an elevated temperature. The preforms can be made using yarns or woven fabrics or they can be filament-wound or braided three-dimensional shapes. The infiltration takes place in a reactor which is connected to an efflu

Source officielle

https://en.wikipedia.org/wiki/Chemical_vapor_infiltration

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Study and characterization of silicon metal alloys systems for the reactive infiltration process of ceramic matrix composites

Manoj Kondibhau Naikade

Silicon infiltrated silicon carbide (SiSiC) is one of the most promising and economical non-oxide ceramic matrix composites for high-temperature structural applications. In recent years infiltration by Si-alloys instead of pure Si has become popular to avoid the presence of residual pure Si by replacing it with higher melting silicides. Apart from this beneficial aspect of using Si-alloys, the downsides and limitations have not received much attention and are hence not well understood. The thesis aims at developing a fundamental understanding of the reactive infiltration of carbonaceous preforms by molten Si-X alloys in general. This is achieved by developing analytical models and designing experiments to individually study various factors like wettability, porosity and pore size distribution, alloy composition, and the preform composition. The near eutectic binary Si-Zr system is used to perform experiments to observe the conjectured phenomena.

EPFL2021

Chargement

Aluminum nitride (AlN) has been applied to various applications, including electronic substrates and packaging, semiconductor production components, wide band gap semiconductor, light-emitting diodes (LED) and acoustic wave devices; at the same time, it is also attractive as a reinforcement in Metal Matrix Composites (MMCs) for thermal management applications with tailored thermal properties. In this thesis, two main subjects are investigated in terms of both the composite processing and its thermal property, namely (i) the high-temperature wettability between AlN and liquid metals and (ii) the thermal conductivity behavior of AlN reinforced metal matrix composites and the associated question of the interface thermal conductance at the AlN/metal interface. High-temperature wettability of AlN particle preforms with pure Al, Cu, Sn and Pb, was investigated by means of drainage curve measurements during pressure infiltration. The measured drainage curves show good agreement with the semi-empirical model in soil science proposed by Brooks and Corey. The total work of immersion, Wi, can be directly calculated by integration of the drainage curves, in turn giving the apparent contact angle during infiltration at high temperature. For Cu, Sn and Pb, the apparent contact angles deduced by integration of experimental drainage curves are in the range 120-140° and agree well with corresponding sessile drop data from the literature. Data for AlN and α-Al2O3 are furthermore similar for both methods of measurement, which results from the presence of a native oxide layer on the AlN particles, which is not eliminated from the particle surface in these systems. For the wettability between AlN/Pb and α-Al2O3/Pb systems, a slight difference is observed and this behavior is attributed to the transformation of the native oxide layer with temperature and the presence of dissolved oxygen in the melt. On the contrary, the wettability of AlN/Al system gives higher value than the sessile drop data measured in vacuum, corresponding rather to the value measured under He-H2 gas at 1373K. This indicates that in the present study there is no elimination of the native oxide layer on the AlN by the formation of Al2O gas, which normally occurs in high vacuum. Moreover, the results of the present technique gradually deviate to the sessile drop data as the initial contact angle gets close or below 90° especially in the α-Al2O3/Al system, suggesting that there is a minimum value, around 105-110°, below which the present infiltration-based contact-angle measurement technique may lose validity. Thermal conductivity behavior of AlN reinforced metal matrix composites produced by pressure infiltration technique has been characterized at both room and elevated temperature in two different microstructural systems, namely (i) particle reinforced system (PRCs) and (ii) partially sintered particle system, i.e., an interpenetrating composite in which the AlN is also a continuous phase (IPCs). The phase contrast of thermal conductivity between AlN (Κd) and matrix metals (Κm) is varied within a range of 0.4

EPFL2008

Chargement

Capillarity in Pressure-Infiltration of Ceramic Particle Preforms by Molten Metal

Alain Léger

EPFL2014

Chargement

EPFL2008