High-Temperature Melt-Infiltrated Composites

The HiPerComp family of ceramic matrix composites, based on silicon melt infiltration composite technology invented by GE, offer a unique combination of high temperature thermal and mechanical properties that make them highly suited for gas turbine engine... 

The widely used fabrication processes for ceramic matrix composite are chemical vapor infiltration (CVl), pol3mier impregnation and pyrolysis (PIP), and reaction melt infiltration (RMl). All of them can also be utilized to fabricate ultra high temperature ceramic matrix composite. 

For the N22 CMC system, remaining open porosity in the CVI SiC matrix was filled by room-temperature infiltration of SiC particulate or slurry casting, followed by the melt-infiltration (MI) of silicon metal near 1400°C. This yielded a final composite with 2% closed porosity within the fiber tows and 0% porosity between the tows. The final composite system (often referred to as a slurry-cast MI composite) typically displayed a thermal conductivity about double that of a full CVI SiC composite system in which the CVI matrix process was carried to completion. Also the composite did not require an oxidation-protective over-coating to seal open porosity. Decreasing the porosity of the hybrid matrix also increased the N22 CMC elastic modulus, which in turn contributed to a high proportional limit stress. However, since the filler contained some low-modulus silicon, the modulus increase was not as great as if the filler were completely dense SiC. 

As high performance ceramic matrix composite systems, such as Melt Infiltrated (MI) SiC/SiC, are being considered for advanced gas turbine engine applications, the characterization of the material becomes more important. A series of tests were conducted where Pt and Ni sheathed Pt thermocouples were used to monitor temperature for short and long duration fast fracture, fatigue and creep tests. While it is known that Si forms eutectics with Pt and Ni, this was initially not considered an issue. But since Ml SiC/SiC composite achieves much of its performance from the infiltrated phase of Silicon (for high conductivity and low porosity), it was felt that further study of possible interactions of the Si phase has to be considered. 

Reactive Melt Infiltration of Carbon Fiber Reinforced Ceramic Composites for Ultra-High Temperature Applications... 

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