Carbon Fiber Reinforced Silicon Carbide Disc Brakes Manufacturing Principles and Processes Matthew Stevens Kanchan Bhattacharyya

Carbon fiber-reinforced silicon carbide (C/SiC) is a development of pure carbon–carbon, a composite material consisting of carbon fiber reinforcement in a matrix of graphite. ● Developed for the nose cones of intercontinental ballistic missiles, it is most widely known as the material for the nose cone and wing leading edges of the Space Shuttle as well as automotive applications such as brake system components on high performance and luxury cars. ● At the IAA in Frankfurt in 1999, the carbon-ceramic brake disk had its world premiere. ● The 2001 Porsche 911 GT2 was the first car to feature carbon-fiber reinforced carceramic brakes ●The use of these materials has revolutionized brake technology, setting new benchmarks in decisive user benefit aspects including safety and durability.

Carbon Fiber Reinforced Silicon Carbide Brake Discs Composed of carbon fiber within a silicone carbide matrix, the ceramic (silicon) is combined with carbon fiber for strength Advantages Include ● Low density ● High mechanical strength and hardness ● High temperature strength ● Oxidation and corrosion resistance even at high temperatures ● Excellent thermal shock resistance ● Excellent Wear resistance ● Low coefficient of thermal expansion ● High thermal conductivity

Advantages of Carbon Fiber Reinforced Silicon Carbide In comparison to the conventional grey cast iron brake disks, Carbon Fiber Reinforced Silicon Carbide discs offer substantial improvements over the dynamics of sports/luxury cars in several fundamental areas: ● Tremendous Weight Advantage (65% compared to Cast Iron) → Reduces suspension weight, improving brake responses, as well as steering behavior and pedal feel. ● 60% Increased Life Span → Cast Iron wears out quickly due to the intense heat friction generated when you brake a car with a powerful engine. Silicone Carbide is heat resistant up to 1830°F and exhibits superior durability to that of Cast Iron → This heat resistance as well as the resistance to thermal shock contribute to the life-span of SiC brake discs. Silicon Carbide Brake Disc Temperature Distribution Gray Cast Iron Brake Disc Temperature Distribution

Advantages of Carbon Fiber Reinforced Silicon Carbide In comparison to the conventional grey cast iron brake disks, Carbon Fiber Reinforced Silicon Carbide discs offer substantial improvements over the dynamics of sports/luxury cars in several fundamental areas: ● Tremendous Weight Advantage (65% compared to Cast Iron) → Reduces suspension weight, improving brake responses, as well as steering behavior and pedal feel. ● 60% Increased Life Span → Cast Iron wears out quickly due to the intense heat friction generated when you brake a car with a powerful engine. Silicone Carbide is heat resistant up to 1830°F and exhibits superior durability to that of Cast Iron → This heat resistance as well as the resistance to thermal shock contribute to the life-span of SiC brake discs. ● Superior Strength and Resistance to Fracture → Carbon Fiber reinforcement increases tensile strength → Induced Stresses result in smaller strains → Ultimately allows SiC brake discs to live as long as the car Silicon Carbide Brake Disc Stress Distribution Silicon Carbide Brake Disc Temperature Distribution Gray Cast Iron Brake Disc Stress Distribution Gray Cast Iron Brake Disc Temperature Distribution

Advantages of Carbon Fiber Reinforced Silicon Carbide In comparison to the conventional grey cast iron brake disks, Carbon Fiber Reinforced Silicon Carbide discs offer substantial improvements over the dynamics of sports/luxury cars in several fundamental areas: ● Tremendous Weight Advantage (65% compared to Cast Iron) → → Reduces suspension weight, improving brake responses, as well as steering behavior and pedal feel. ● 60% Increased Life Span → Cast Iron wears out quickly due to the intense heat friction generated when you brake a car with a powerful engine. Silicone Carbide is heat resistant up to 1830°F and exhibits superior durability to that of Cast Iron → This heat resistance as well as the resistance to thermal shock contribute to the life-span of SiC brake discs. ● Superior Strength and Resistance to Fracture → Carbon Fiber reinforcement increases tensile strength → Induced Stresses result in smaller strains → Ultimately allows SiC brake discs to live as long as the car Silicon Carbide Brake Disc Stress Distribution Silicon Carbide Brake Disc Strain Distribution Gray Cast Iron Brake Disc Stress Distribution Gray Cast Iron Brake Disc Strain Distribution ● Enchanced Chemical Stability & Corrosion Resistance → Complete Corrosion Resistance against weather and harsh road conditions via non-iron based surface, also enhancing durability

Polymerizing Resin (Curing) What Are Resins? - Resins are a broad class of substances that share the quality of being viscous liquids that can harden permanently but otherwise can have great variety in chemistry and origin. (synthetic or plant derived) They can be classified as thermoplastics or thermosets. Thermoplastics – can be softened when heated or harden when cooled repeatedly without much effect on their long-term chemical nature. They are formed by addition polymerization and have long molecular chain structures.  Examples of Carbon Thermoplastic Resins for Carbon Matrix Composites: Pitches or coal tar. Thermosets – harden during the molding process under high heat and cannot be softened once solidified – permanent setting resins. This is due to 3D cross-linking and strong covalent bonding. They are formed by condensation polymerization and are stronger and harder than thermoplastic resins. They are hard, rigid, water resistant, and scratch resistant.  Examples of Carbon Thermosetting Resins for Carbon Matrix Composites: Phenolics, ruran resin, oxidized polystyrene, polyvinyl alcohol. The class of carbon thermosetting resins are predominant in ceramic matrix composite disc brake manufacturing for their durability. What is curing? - A heat-influenced molding process (200-300°C )where bond formation gradually increases the length and degree of cross-linking between oligomers (polymers of small size) until a 3D network of chains is created. Initially, the resin viscosity drops when heat is applied, reaches a minimum where the resin is most fluid, and then rises as the molecular polymer network is being formed until the resin solidifies. - At this stage, the resin and the impregnated carbon fibers are termed “pre-ceramic polymer”.

Pyrolysis What is Pyrolysis? - Pyrolysis is a thermochemical decomposition process carried out at temperatures of 800-1300°C which decomposes hydrocarbon-based substances (like the “pre-ceramic polymer”) in the absence of oxygen or reactive halogens. - Volatile liquid and gaseous byproducts including CO, H2,CO2, CH2, H2O are released leaving behind a porous carbon ceramic matrix. - Pore size must be carefully monitored at this stage for Liquid Silicon Infiltration (LSI) to succeed later on. - At this stage, the “pre-ceramic polymer” has now become a “porous carbon preform”.

Liquid Silicon Infiltration (LSI) What is LSI? - In Liquid Silicon Infiltration (LSI), the “porous carbon perform” is infiltrated by molten silicon at a temperature above its melting point at 1414°C. - The liquid silicon melt is drawn up into the porous structure by capillary action often along with external vacuum suction and reacts with the solid carbon to form silicon carbide (SiC). The pore channel size achieved in pyrolysis determine the quality of the silicon carbide (SiC) matrix in terms of reaction completion and infiltration. Very large pores help obtain a complete infiltration but result in an incomplete chemical interaction with high residual free silicon and unreacted carbon. Very small pores result in more complete chemical interaction but incomplete infiltration due to blockage of channels. In general, at least 5% residual free silicon is left in the silicon carbide matrix. - LSI yields a matrix of low porosity with high thermal and electrical conductivity at a low cost and short production time.