| 摘要 |
A titanium engine valve is fabricated with discrete head and stem portions, preferably joined by inertia welding and/or diffusion bonding. The joint between the head and stem portions is located well up on the valve stem so that it is not exposed below the valve guide. The head portion, including a fillet region and lower stem region, is composed of a first material comprising titanium, such as a conventional high strength titanium alloy. Alternatively, the head portion may consist of a cast or forged heat treated TIC. The stem portion, which is not directly exposed to the hostile environment of the combustion chamber, is composed of a second material comprising titanium, such as mill annealed titanium alloy rod stock. The resulting valve is, therefore, much less expensive to manufacture than a conventional titanium valve without sacrificing any mechanical characteristics in the portions of the valve subjected to high stress and temperature. |
