Metal treatment – Process of modifying or maintaining internal physical... – With measuring – testing – or sensing
Reexamination Certificate
2000-03-24
2001-12-25
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With measuring, testing, or sensing
C148S671000
Reexamination Certificate
active
06332935
ABSTRACT:
This invention relates to the processing of titanium alloys, and, more particularly, to the processing of billets of titanium-base alloys to permit low-noise ultrasonic inspection at the conclusion of the processing.
BACKGROUND OF THE INVENTION
Large articles of alpha-beta titanium-base alloys may be produced by casting the titanium alloy into a mold and mechanically working the cast ingot to a smaller size termed a billet. The mechanical working is typically accomplished by forging (although not the forging approach of the present invention) to accomplish the size reduction. After the mechanical reduction, the billet is further shaped, for example by additional forging and/or machining, to the final desired shape.
Large titanium-alloy forgings are often used for aerospace parts which must meet stringent requirements before they may be placed into service. For this reason, between the forging operation and the final shaping operation the billet is inspected ultrasonically to assess whether its quality is suitable for the final processing and eventual service. The ability of the ultrasonic inspection to detect flaws is limited by the noisiness inherent in the ultrasonic testing. In many cases, the noisiness results from interference from the material structure rather than from the testing technique, the electronic capabilities, and similar sources.
Several approaches have been utilized to improve the ultrasonic testing of the billet. In one, the ultrasonic inspection procedures have been improved but are not fully successful in avoiding interference by noise. In another approach, as described in U.S. Pat. No. 5,277,718, there is a heat treatment after the forging but before ultrasonic inspection. This heat treatment, while improving inspectability, may interfere with the subsequent processing of the billet.
There is a need for an improved approach to the processing of billets of alpha-beta titanium alloys, particularly those billets that are to be subsequently beta-processed after the billet stage. The improved approach should permit ultrasonic inspection of the billets with low interference from noise, and also be compatible with subsequent processing of the billets into articles. The present invention fulfills this need, and further provides related advantages.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method for processing workpieces of alpha-beta titanium-base alloys, particularly those that are to be beta-processed subsequent to the billet stage. The approach results in a billet that is readily suited both for ultrasonic inspection and for further processing to useful articles. Relatively large billets may be forged by this approach. The microstructure of the finished billet is selected to minimize noise and undesirable reflections in ultrasonic testing, so that ultrasonic testing is optimally performed to evaluate the interior structure of the billet. The process of the invention is readily and economically performed using available machinery and furnaces.
A processing method is practiced on a starting workpiece of a titanium-base alloy having a temperature-composition phase diagram with a beta region and an alpha-beta region separated by a beta transus temperature. The method includes first forging the starting workpiece at a first temperature above the beta transus temperature in the beta region to form a billet, thereafter second forging the billet at a second temperature below the beta transus temperature in the alpha-beta region, and thereafter third forging the billet at a third temperature above the beta transus temperature in the beta region. Optionally, the billet is quenched, preferably by water quenching, after the third forging step. Optionally, the billet may be annealed and/or further worked by beta-processing after the third forging step. The billet is typically ultrasonically tested after the third forging step in this embodiment. The cross sectional shape of the billet may be varied during the forging process to obtain optimal results.
In a further embodiment of the invention, there is an additional step, after the step of third forging, of fourth forging the billet at a fourth temperature below the beta transus temperature in the alpha-beta region. The result is more-desirable mechanical properties for subsequent processing. The step of fourth forging preferably accomplishes a reduction in cross-sectional area of the billet of up to about 40 percent, more preferably from about 5 to about 40 percent, and most preferably from about 5 to about 15 percent. Optionally, the forged billet may be annealed after the fourth forging step. Ultrasonic testing is performed after the fourth forging step in this embodiment. Optionally, the billet may be further worked by beta-processing after the ultrasonic testing. As in the prior embodiment, the shape of the billet may be varied during the course of the forging process.
The approach of the invention produces a billet with randomly oriented interfaces between crystallographically aligned regions of transformed beta structure. With relatively little or no deformation after the third forging step in the beta region, this microstructure is retained. This microstructure has been found to be favorable to produce large billets that may be ultrasonically inspected with relatively low noise. While the use of no fourth forging step in the alpha-beta region is within the scope of the invention and yields very low noise in ultrasonic testing, there may optionally be a small reduction in cross-sectional area by alpha-beta forging in the fourth step to impart additional ductility to the forging so that it may be more readily handled in a production environment and in further processing.
The present invention thus provides a technique for producing a billet of an alpha-beta titanium alloy that is readily inspected by ultrasonic techniques and is suitable for further processing into a wide range of articles. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
REFERENCES:
patent: 3470034 (1969-09-01), Kastanek et al.
patent: 5277718 (1994-01-01), Paxson et al.
patent: 63206457 (1988-08-01), None
patent: 08049053 (1996-02-01), None
Database INSPEC, Institute of Electrical Engineers, Stevenage, GB; Pam JH et al.: “Influence of different forging processes on the ultrasonic response in titanium alloys TC6 and TC11”. XP-002171168 (Abstract) no date.
Gorman Mark D.
Woodfield Andrew P.
General Electric Company
Hess Andrew C.
Kastler Scott
Narciso David L.
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