Method of making Carbon/Ceramic matrix composites

Abstract

A method of making high performance friction materials with tailored levels of a ceramic hard phase to achieve optimum thermal conductivity, friction coefficient and wear performance of composite brake materials. In accordance with one method of the invention specific end-use application friction requirements are satisfied by tailoring the level of carbon in a selected carbon/carbon preform, heat treating the carbon/carbon composite preform, thereby affecting thermal conductivity so as to optimize overall braking performance prior to ceramic processing and by selecting an optimum level of ceramic hard phase to achieve satisfactory friction disc wear life and friction characteristics of the braking material.

1 . A method of making a carbon/ceramic matrix composite having a specific carbon/ceramic composition with tailored levels of a ceramic hard phase and a soft carbon/carbon phase to achieve optimum thermal conductivity, friction coefficient and wear performance and correlating the resulting composite properties with vehicle braking performance requirements, the method comprising the steps of:
 (a) infiltrating a first carbon fiber substrate with pyrolytic carbon to reach the specific carbon/carbon density of approximately 1.68 g/cc to approximately 1.73 g/cc with appropriate porosity level suitable for impregnation with a pre-ceramic polymer to form a carbon/carbon preform and heating said carbon/carbon preform to between about 1600 degrees C. and about 2500 degrees C. to form a heat-treated carbon/carbon preform;   (b) impregnating said heat-treated carbon/carbon preform with a pre-ceramic polymer to form a first impregnated preform;   (c) heating said first impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a first cured preform;   (d) heating said first cured preform to a temperature of about 1,000 degrees C. for about one hour to form a first impregnated and pyrolyzed preform;   (e) impregnating said first impregnated and pyrolyzed preform with a pre-ceramic polymer to form a second impregnated preform;   (f) heating said second impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a cured second impregnated preform;   (g) heating said cured second impregnated preform to a temperature of about 1,000 degrees C. for about one hour to form a pyrolyzed second impregnated preform;   (h) machining said pyrolyzed second impregnated preform to prepare said pyrolyzed second impregnated preform for a third impregnation cycle to form a machined pyrolyzed second impregnated preform;   (i) impregnating said machined pyrolyzed second impregnated preform with a pre-ceramic polymer to form an impregnated third impregnated preform;   (j) heating said third impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a cured third impregnated preform;   (k) heating said cured third impregnated preform to about 1600 degrees C. for about eight hours to produce a pyrolyzed third impregnated preform;   (l) machining said pyrolyzed third impregnated preform to form a fourth impregnated preform;   (m) heating said fourth impregnated preform to a temperature of about 1000 degrees C. to form a heated fourth impregnated preform;   (n) infiltrating said heated fourth impregnated preform with methane gas to form a first friction disc;   (o) machining said first friction disc to final dimensions to form a final friction disc;   (p) subjecting said final friction disc to dynamic testing to determine its strength and friction characteristics; and   (q) correlating said strength and friction characteristics with vehicle braking performance requirements.   
   
   
       2 . The method as defined in  claim 1  in which the first carbon fiber substrate is constructed from rayon precursor fibers. 
   
   
       3 . The method as defined in  claim 1  in which the first carbon fiber substrate is constructed from polyacrillonitrile fibers. 
   
   
       4 . The method as defined in  claim 1  in which the first carbon fiber substrate is constructed from pitch fibers. 
   
   
       5 . The method as defined in  claim 1  in which the first carbon fiber substrate is constructed from three dimensional, needled carbon fiber preforms. 
   
   
       6 . The method as defined in  claim 1  in which the first carbon fiber substrate comprises an eight harness satin graphite fabric laminate. 
   
   
       7 . The method as defined in  claim 1  in which the first carbon fiber substrate comprises a chopped graphite fiber molding compound. 
   
   
       8 . The method as defined in  claim 1  in which said final friction disc is further tested to determine its compressive strength, fracture toughness and thermal conductivity. 
   
   
       9 . The method as defined in  claim 1  in which said final friction disc is further tested to determine the density and degree of porosity of said final friction disc. 
   
   
       10 . The method as defined in  claim 1  further comprising the steps of;
 (a) infiltrating a second carbon fiber substrate with pyrolytic carbon to reach the specific carbon/carbon density of approximately 1.15 g/cc to 1.3 g/cc with appropriate porosity level and heat-treating the carbon/carbon preform to between about 1600° C. and about 2500° C. suitable for impregnation with a pre-ceramic polymer to form a second porous precursor substrate;   (b) impregnating said second porous precursor substrate with a pre-ceramic polymer to form an alternate first impregnated part;   (c) heating said alternate first impregnated part within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a cured alternate first impregnated part;   (d) heating said cured alternate first impregnated part to a temperature of about 1,000 degrees C. for about one hour to form an alternate first impregnated and pyrolyzed preform;   (e) impregnating said alternate first impregnated preform with a pre-ceramic polymer to form an alternate second impregnated preform;   (f) heating said alternate second impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a cured alternate second impregnated preform;   (g) heating said cured alternate second impregnated preform to a temperature of about 1,000 degrees C. for about one hour to form an a pyrolyzed alternate second impregnated preform;   (h) machining said pyrolyzed alternate second impregnated preform to prepare the preform for the third impregnation cycle;   (i) impregnating said alternate second impregnated and machined preform with a pre-ceramic polymer to form an alternate third impregnated preform;   (j) heating said alternate third impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form a cured alternate third impregnated preform;   (k) heating said alternate third impregnated preform to about 1000° C. for one hour to produce a pyrolyzed alternate third impregnated preform;   (l) impregnating said pyrolyzed alternate third impregnated preform with a pre-ceramic polymer to form an alternate fourth impregnated preform;   (m) heating said alternate fourth impregnated preform within an inert gaseous atmosphere to a temperature of about 400° C. for about one hour to form a cured alternate fourth impregnated preform;   (n) heating said cured alternate fourth impregnated preform to a temperature of about 1,000 degrees C. for about one hour to form an alternate fourth pyrolyzed impregnated preform; and   (o) machining said alternate fourth pyrolyzed impregnated preform to prepare the preform for the fifth impregnation cycle.   
   
   
       11 . The method as defined in  claim 10  in which said second porous precursor substrate is constructed from rayon precursor fibers. 
   
   
       12 . The method as defined in  claim 10  in which said second porous precursor substrate is constructed from polyacrillonitrile fibers. 
   
   
       13 . The method as defined in  claim 10  in which the second carbon fiber substrate is constructed from pitch fibers. 
   
   
       14 . The method as defined in  claim 10  in which second porous precursor substrate is constructed from three dimensional, needled carbon fiber_preforms. 
   
   
       15 . The method as defined in  claim 10  in which the second carbon fiber substrate comprises a chopped graphite fiber molding compound. 
   
   
       16 . The method as defined in  claim 10  in which the second carbon fiber substrate comprises eight harness satin graphite fabric. 
   
   
       17 . The method as defined in  claim 10  further comprising the steps of:
 (a) impregnating said alternate machined fourth impregnated preform with a pre-ceramic polymer to form an alternate fifth impregnated preform;   (b) heating said alternate fifth impregnated preform within an inert gaseous atmosphere to a temperature of about 400 degrees C. for about one hour to form an alternate cured fifth impregnated preform;   (c) heating said alternate cured fifth impregnated preform to about degrees C. for about eight hours to produce an alternate fifth pyrolyzed impregnated preform;   (d) machining said alternate fifth impregnated preform to form an alternate final friction disc;   (e) subjecting said second alternate final friction disc to dynamic testing to determine its strength and friction characteristics; and   (f) comparing the dynamic testing of said alternate final friction disc with the dynamic testing of said final friction disc.