Abstract
In this work, the mechanisms leading to the pore closure in reactive melt infiltration (RMI) of carbon by pure silicon and a near eutectic Si-8 at-pct Zr alloy at 1500 and 1700 °C under vacuum were studied. Various geometrical configurations of microchannels were fabricated via laser ablation of glassy carbon plates. The micron size capillary channels allowed simplifying the complicated porosity distribution in the infiltration of powder or fibres based porous preform while keeping the physical dimensions in the range of where the physical phenomenon of pore closure takes place. The extent of infiltration was analysed by means of X-ray radiography. For RMI of pure Si, the widely accepted decrease in capillary radius by the formation of a solid state SiC layer by the reaction of liquid Si and C was observed, but did not lead to closure and it is hence not the infiltration limiting step in channels as small as 10 μm. However, in the case of the Si-Zr alloy infiltration, another mechanism of pore closure was observed, namely the precipitation of zirconium silicides at the infiltration front, due to Zr enrichment in the alloy by the continuous consumption of Si for the formation of SiC.
Highlights
Silicon infiltrated silicon carbide (Si-SiC), first developed by Popper in 1960s [1], has gained popularity as an industrial ceramic material, known for its remarkable properties, such as low porosity, low density, high thermal conductivity, high mechanical strength, excellent chemi cal, oxidation and thermal shock resistance and high wear and corrosion resistance [2,3]
They can be obtained from different constituents and processes [4,5,6,7], the fabrication concept is based on the reactive melt infiltration (RMI) process, known as liquid silicon infiltration (LSI) in the case of Si infiltration
The general idea consists of infiltrating a porous carbonaceous preform by liquid Si to attain a fully dense Si-SiC composite
Summary
Silicon infiltrated silicon carbide (Si-SiC), first developed by Popper in 1960s [1], has gained popularity as an industrial ceramic material, known for its remarkable properties, such as low porosity, low density, high thermal conductivity, high mechanical strength, excellent chemi cal, oxidation and thermal shock resistance and high wear and corrosion resistance [2,3]. Increasing interest led to the development of many variants, such as monolithic and particle or fibre reinforced ceramic matrix composites (CMC) They can be obtained from different constituents and processes [4,5,6,7], the fabrication concept is based on the reactive melt infiltration (RMI) process, known as liquid silicon infiltration (LSI) in the case of Si infiltration. Various ap proaches have been made to overcome these issues, such as including inert interphase such as SiC or BN, by chemical vapour deposition (CVD) of carbon fibres followed by infiltration. These techniques, being effective, remain expensive in terms of processing and equipment
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