Metal matrix composite (MMC) engine components for high performance racing applications were produced using the PRIMEX™ pressureless metal infiltration process. Utilization of these composites resulted in significant weight reduction and performance benefits for each component.
The metal matrix composites which were evaluated consisted of aluminum alloys reinforced with 45-65 volume percent of either aluminum oxide or silicon carbide particulates. The high volume fraction of reinforcing particles resulted in significant increases in yield strength, stiffness, and wear resistance, while a significant decrease in the coefficient of thermal expansion was achieved as compared with unreinforced aluminum alloys.
The tested metal matrix composite components included valve spring retainers, fuel pump pushrods, and transmission brake valves.
Valve spring retainers, weighing approximately 40% of comparable steel parts, were subjected to high speed testing for up to 16 hours (equivalent to running four 500 mile races) without showing any wear damage. Some wear damage was noted on the steel spring dampeners. This situation could be corrected by design or material changes. Improvements in retainer mechanical design or MMC strength are being investigated to survive testing under severe valve float conditions.
Fuel pump pushrods, weighing approximately 30% of comparable steel parts, were tested for 93 hours without detectable wear. Transmission brake valves were subjected to 25 start/stop cycles of dynamometer and vehicle testing. The valves successfully completed these tests with no evidence of wear.