This invention relates to the joining of an X-ray tube target assembly. More particularly, it relates to the joining of the graphite disk to the metallic layer portion wherein titanium, or its alloys are used as the brazing material and the vapor pressure of the joint is controlled.
In producing new and improved targets for rotary anode X-ray application, it would be desirable to have the anode operate at or above a braze joint temperature of 1375.degree. C. Presently, platinum brazed anodes operate at temperatures closer to 1300.degree. C. These targets are braze joint limited, and if the operating temperature could be made higher, then these tubes could run more aggressive protocols. Recently employed X-ray tubes are projected to run at about 1400.degree. C. in accordance with their more aggressive protocol.
It is known from a strength standpoint, that a titanium braze can withstand cap warpage up to 1800.degree. C. under isothermal heating conditions. Cap warpage is caused by the difference in the coefficients of thermal expansion between the molybdenum substrate and the tungsten focal tract causing the molybdenum substrate to depress at the top and expand at the bottom. However, based on physical property data, the sublimation of the titanium braze joint should become significant at braze joint temperatures greater than 1375.degree. C. In the tube, therefore, the braze joint could contribute to high voltage instability if the target should operate at temperatures above 1375.degree. C. The prior art does not provide a solution to the sublimation problem.
It is, therefore, an object of the present invention to provide an improved composite X-ray target with a brazed interconnection having improved bond strength and with higher operating temperature characteristics. Another object of the present invention is to provide an improved method of brazing composite X-ray tube targets. Yet another object of the present invention is to provide an improved method of the foregoing type wherein the vapor pressure of the braze joint metal is controlled.
These objects and other features and advantages will become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.