| 摘要 |
A method is disclosed for making a dual microstructure titanium based engine valve, wherein a first zone of the valve contains essentially a mixture of fine, equiaxed alpha and transformed beta crystalline grains which exhibit high tensile strength and high fatigue resistance, and a second zone of the valve which contains essentially a colony type microstructure exhibiting resistance to high temperature creep. The method comprises: (a) preparing a valve stock of forgeable mixed phase alpha/beta titanium based material; (b) hot working said first zone at a temperature below the beta transus temperature, (c) forging said second zone and, either simultaneously with said forging or subsequent thereto, heat treating said second zone at a temperature above (e.g., 25 DEG -200 DEG F. above) the beta transus temperature for a period of time to achieve beta processing followed by cooling to 1400 DEG F. at a rate of 0.1-10.0 DEG F./second; and (d) heat treating, immediately subsequent to either step (b) or step (c), at least the first zone at a temperature below the beta transus temperature (e.g., 25 DEG -200 DEG F. below) for a period of time to achieve alpha/beta processing. |
