Composite Fabrication

The LP-30SC SiC fiber has been used to make several composite coupons in order to demonstrate the high temperature capability of the material, in essence proving that the FFF SiC fibers can withstand extreme processing temperatures to make an advanced composite material system.  The first articles fabricated were based on the glass-ceramic matrix composite (GCMC) concept, in which an aluminasilicate glass material is introduced as the matrix phase and then undergoes an initial ‘ceramicization’ during the cool-down process in order to drive light crystallization.  Barium magnesium aluminasilicate (BMAS) and barium strontium aluminasilicate (BSAS)-based GCMCs were produced.  The BSAS fabrication hot pressing process involved a 30 minute hold at 1550oC at 3 tons applied load in argon.  Similarly, a hot reactive pressing procedure was used to produce a zirconium carbide-silicon carbide matrix with the LP-30SC SiC fiber included as reinforcement.  The hot pressing schedule included a 1 hour hold at 1900oC in argon with 30 MPa stress applied.  In both cases, the composite samples were sectioned and evaluated for evidence of fiber degradation and chemical interaction with the surrounding matrix, based on loss of fiber integrity and bubbling in the matrix (indicating gases CO and CO2 gases released from chemical attack and breakdown of the SiC fiber).  As seen in both microscopy images below, the LP-30SC fiber survived and remained viable through the aggressive composite processing.

BSASmatrix / SiCfiber cross-section (hole is evidence of fiber pullout during coupon fracture)

ZrC-SiCmatrix / SiCfiber cross-section

Similar studies were done with the FFF silicon nitride (Si3N4) fibers included as the reinforcement for a boron nitride (BN) matrix phase composite.  These coupons were hot pressed at 1800oC for hour in nitrogen at 50 MPa applied stress.  Microscopy images (including the one shown below) were taken of the cross-section showing the random orientation of the Si3N4 fibers in the matrix.  Like the FFF SiC fibers, the Si3N4 fibers revealed no signs of degradation from the composite processing steps.