The Boeing Company

Larry E Nitzsche

Jean Ann Nielsen

Herbert S Goode, Jr

The plasma descaling process of the present invention removes surface oxides selectively from structural metal surfaces, especially titanium and its alloys, and, with appropriate control of the reaction temperature, is self-limiting to avoid cracking problems otherwise associated with intergranular attack. In a preferred embodiment of the present invention, a fluoride plasma reacts with surface oxides on a titanium alloy to remove scale and alpha case in a temperature controlled chamber without attacking the underlying crystalline metal to cause intergranular attack. Properly controlled by regulating the chamber temperature, the plasma reaction terminates when the plasma has removed the surface oxides and encounters the underlying crystalline metal. The product is a metal surface free of scale and alpha case and free of intergranular attack. The plasma descaling process replaces conventional metal finishing processes, such as chemical milling or etching.

Plasma descaling of metals

The invention provides a method of removing surface scale from a titanium or titanium alloy substrate. The method includes the steps of heating the substrate to a temperature in the range from about 100.degree. C. to about 600.degree. C., and thereafter subjecting the heated surface to a plasma formed from a gas selected from the group of consisting of CF.sub.4 and SF.sub.6. The plasma reacts with the surface scale, removing the scale, without attacking the underlying crystalline titanium or titanium alloy. Properly controlled, the plasma reaction terminates when the plasma has penetrated the scale and encounters the underlying crystalline metal. As a result, the method of the invention is capable of uniform removal of the entire surface scale of a crystalline titanium-containing substrate, without intergranular attack of the substrate.

Growing community of inventors

Bellevue, WA, United States of America

Larry E Nitzsche