Patent ID: 7998376

Claim:
A method for reducing lot-to-lot variability in the friction performance of carbon-carbon composite brake discs, the method comprising the sequential steps of: (a) carbonizing an annular nonwoven carbon fiber brake disc preform at a temperature between about 1400° C. and 2540° C. in an inert (nitrogen or vacuum) atmosphere; (b) carrying out a first densification of the carbonized carbon fiber preform by chemical vapor deposition (“CVD”) or chemical vapor infiltration (“CVI”) to produce a carbonized fiber preform: (i.) having a rough laminar microstructure and a density of about 1.4 grams per cubic centimeter; (ii.) having a smooth laminar microstructure and a density of about 1.2 grams per cubic centimeter; or (iii.) having an isotropic microstructure and a density of about 1.0 gram per cubic centimeter and to reduce variability of the carbon microstructure of carbon matrix material adjacent to said carbon fiber; (c) densifying the product of step (b) with isotropic pitch by vacuum pitch infiltration (“VPI”) processing to a density of approximately 1.3-1.6 grams per cubic centimeter; (d) carbonizing the preform at a temperature between about 1200° C. and 2000° C. in an inert (nitrogen or vacuum) atmosphere to remove non-carbon volatiles from the pitch and to open porosity in the pitch-infused preform; (e) densifying the product of step (d) with isotropic pitch by vacuum pitch infiltration (“VPI”) processing to a density of approximately 1.75 grams per cubic centimeter; (f) carbonizing the preform at a temperature between about 1200° C. and 2000° C. in an inert (nitrogen or vacuum) atmosphere to remove non-carbon volatiles from pitch and to open porosity in the pitch-infused preform; and (g) subjecting the resulting pitch-densified carbon-carbon composite brake disc preform to a final heat-treatment step at a temperature between 1600° C. and 2000° C. in an inert (nitrogen or vacuum) atmosphere.