Abstract
A relation for an adequate pore fraction needed to obtain residual Si and C free composites via reactive Si-X alloy infiltration is presented. The volume ratio of SiC and carbonaceous phase, the composition of the infiltrating liquid and the apparent density of the preform are used as design entities. The approach allows identifying combinations of these design entities leading to desirable microstructures, e.g. those free of residual silicon or free of excess graphite. The approach gives further access to important post infiltration characteristics like propensity of the various phases.An idealising mathematical model describing the reactive flow of Si-X alloy in a single micron sized capillary channel of carbon as well as in carbonaceous preforms is presented. The model is further expanded to evaluate the infiltration depth in porous carbonaceous preform for a given composition of Si-X alloy and infiltration temperature. The model is presented for both isothermal and non-isothermal cases.The analysis is formulated in general terms and is hence applicable to a large variety of Si-C-refractory metal systems of potential interest.
Highlights
Liquid silicon infiltration (LSI) into carbonaceous preforms com bined with in situ conversion reaction of silicon with carbon to SiC is widely believed to be the most promising and cost-effective route to produce SiC parts [1,2,3,4]
This can be seen by looking at the molar volume of liquid silicon at its melting temperature in the 10.8 cm3 ballpark while SiC has a molar volume of the compound, i.e. for 1 mo of Si and 1 mo of C, 12.5 cm3 roughly
While there is some latitude in the molar volume of the carbonaceous material, ranging from 3.4 cm3 for diamond to about 8 cm3 for glassy carbon, the sum of the molar volumes of liquid Si and the carbonaceous material will always be larger than that of SiC
Summary
Liquid silicon infiltration (LSI) into carbonaceous preforms com bined with in situ conversion reaction of silicon with carbon to SiC is widely believed to be the most promising and cost-effective route to produce SiC parts [1,2,3,4]. The ramifications of the LSI process both in terms of phases present and conditions for fully dense and fully converted preforms as well as in terms of premature blocking of infiltration by solid silicide phase for mation have so far not been discussed in an analytical way in the liter ature It is the aim of the present paper to (i) provide general expressions for the adequate preform constitution to obtain fully dense, fully con verted SiC/silicide solids in net shape by the LSI process and to (ii) develop an analytical framework to quantitatively predict accessible infiltration depth by spontaneous infiltration of silicon-rich alloys con taining silicide formers.
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