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The recent development of TiAl-based alloys by the aerospace community has provided an excellent material alternative for hot components in automotive engines. The low density combined with an elevated temperature strength similar to that of Ni-base superalloys make TiAl-based alloys very attractive for exhaust valve applications. Lighter weight valvetrain components improve performance and permit the use of lower valve spring loads which reduce noise and friction and enhance fuel economy. However, difficult fabricability and a perception that TiAl alloys are high cost, low volume aerospace materials must be overcome in order to permit consideration for use in high-volume automotive applications. This paper provides a comparison of properties for several exhaust valve alternative materials. The density of TiAl alloys is lower than Ti alloys with creep and fatigue properties equivalent to IN-751, a current high performance exhaust valve material.

Titanium alloys offer a unique combination of high strength-to-weight ratio, good corrosion resistance and favorable high temperature mechanical properties. While the high cost of titanium has severely restrained consideration of titanium usage in mass produced automobiles, there are certain components for which titanium alloys are particularly well suited from a design viewpoint. The most promising of these applications include suspension springs and engine components such as valves, valve springs and valve retainers. The technical advantages offered by the use of titanium alloys in these applications include reductions in vehicle weight and improvements in performance, fuel economy and packaging efficiency. This paper reviews characteristics of the several types of titanium alloys.