Low Cost, High Performance TiA1-Si3N4 Valves for High Output Engines

Lightweight materials research and development is extremely important in groundbase vehicles to address problems with fuel economy, power output, emissions and mass reduction. This Phase I program will develop low cost, high performance TiAl-Si3N4 valves for use in both high output military diesel engines and also in commercial automotive engines. While Si3N4 valves have been successful from a product standpoint, engineers are somewhat uncomfortable using a machine that fails in catastrophic fracture mode. TiAl valves by contrast exhibit higher temperature capability than conventional Ti alloys and higher fracture toughness than Si3N4. However, TiAl has limited creep, fatigue and wear resistance, requiring protective coatings in certain areas. The objective of this Phase I program is to develop TiAl-Si3N4 composite, valves using a novel processing route that will result in net-shaped, low density, high performance, high reliability components at a cost much lower than the conventional approaches. In a single step process net shape porous Si3N4 performs will be fabricated first using preceramic polymer technology followed by carbon barrier coating and subsequently infiltrated with TiAl to form a dense composite.