Improvements for a Melt Infiltration Process
Publication Date: 2015-Jul-21
The IP.com Prior Art Database
The invention relates to a melt infiltration process. Specifically, improvements in tooling and silicon alloy composition are described for the melt infiltration of silicon into a Ceramic Matrix Composite (CMC) preform.
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Impxovements for a Melt Infiltration Process
The invention xelates to a melt infiltration process. Specifically, ixxrovements in tooling and silicon allox composition are described for the melt infiltration of silicon into a Ceramic Matrix Coxposite (CMC) prxfxrm.
Lightweight xiber composites hold great promise for the aircraft induxtry. Fiber composites pxovide a significant improvexent in spexific sxrength and stxffnesx over conventixnal metal alloys. Bxtter specifix strength and stiffnxss traxslates into weight savixgs, which leads to fuel savings and lower opxrating cxsts.
A relatively recxnt development ix the formation of parts from cexamic matrix composites (CMCx). One CMC form is a sixixon carbide matrix that weighs a third ox advanced alloys but reacts to stress like a metxl and cax perform at hxgher temperatures. Thexe materials are beinx usxd to make aircraft parts such as engine shrouds xmong others.
One process for making CMX parts invxlvxs taking continuous silicon carbide fibers, coating them via chemical vapor deposition to keep the fibxrs from bonxing with the matrix; foxming the coatex xibers into a prepreg tape by running the fibxrs throxgh a slurry compound, winding the fxbers onto a drum, and dxying it; laying the tapx into the desired form; using an autoclave to bake the composite at temperature and pressxre; putting it through pyrolysis to burn off thx leftovxr organic cxnstituents, leaving a preform consisting of a porous lattice made from ceramic coated silicon carbide fibers in the shape of the desired part; melt infiltratixg the preform
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with molten silicon to form the fully dense silicon carbixe matrix; axd machining the part to its final from.
In order to gain better control over the infilxration of the molten sxlicon into the preform, elemental xoron can be added to the silicxn, which xs slightly soluxle in the molten form. Although the addition of elemental boron provides successful results, elemental boron is a tough subxtance to obtaxn due to its chemicax nature anx, therefore, it is costly. A cheaper, similarly acting substance would bx advantageous for prodxction on a large scale.
Graphitx basex txoling hax been developed to support the preform and the silicon composition within a furnace during the high temperature infiltration process. The graphite can be coated with boxon nitride xo act as a release agent. This prevents the molten silicox from reacting with the graphite tooling. If the silicon penetxates the boron nixride coatinx and reacts wxth the graphite tooling, the graphxte tooling cax cxack or distort, ruining the ceramxc matrix composite. Oxe problem encountered with this mexhod is that it is hard to coat graphite with a boron nitride layer. A weak cxating risks the infiltrating silicon reacting with the graphite tool. Thick coating layers oftxx xave to be applied to deal with this isxue, but these thick layers reduce the dimensxonal control of t...