Fabrication and Properties of SiC/SiC Composites Derived from CERASET(TM) SN Preceramic Polymer
D. Miller, D. Pommell, G. Schiroky
The fabrication of silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) ceramic matrix composites (CMCs) by a polymer infiltration and pyrolysis (PIP) technique is discussed. In PIP processing, fiber preforms are infiltrated with a preceramic polymer, which is then cured and pyrolyzed to form a cermic matrix. Because the density of a preceramic polymer (ca. 1.0 g/cm3) isusually much lower than that of the pyrolyzed matrix, several preform infiltration and pyrolysis cycles must be performed to increase matrix density. Nicalon® fiber-reinforced composite plates were fabricated in the as-cured state by (1) vacuum bag/autoclave processing, (2) resin tranfer molding, (3) resin infusion of C/SiC preforms, and (4) vacuum assisted resin infusion. Lanxide Corporation's CERASET® SN precermic polymer (now called KiON Ceraset Polyureasilazane) was used in all processing techniques to fabricate the SiC/SiC composites plates.
Plates fabricated by vacuum bag/autoclave processing, resin transfer molding and vacuum assisted resin infusion with carbon coated ceramic grade Nicalon ® fabric resulted in CMCs having average room temperature 4-point flexural strengths of 265 MPa, 275 MPa, and 290 MPa, respectively. The best 4-poit flexural strengths, 400 MPa, were achieved via PIP processing to 1000 degrees C of theC/SiC coated ceramic grade Nicalon® fabric preform. Hi-Nicalon® fiber-reinforced composite plates were fabricated using infusion of C/SiC preforms at pyrolysis temperatures ranging from 1300 degrees C to 1600 degrees C. The maximum room temperature 4-point flexural strength, 575 MPa, was demonstrated with a plate whcih was pyrolyzed at 1300 degrees C. The average 4-point flexural strength decreased with increased pyrolysis temperature, presumably due to the degradation of the Hi-Nicalon® fibers at temperatures greater than 1300 degrees C.