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Tantalum Alloy Tubing Development Program

Report Number: AFML TR 67-191
Author: Turner, Fred S.
Corporate Author: Allegheny Ludlum Steel Corporation Research Center
Laboratory: Air Force Materials Laboratory
Date of Publication: 1967-06
Pages: 154
Contract: AF 33(657)-11261
Project: 8108
AD Number: AD0819050

Abstract:
A process has been developed to produce tantalum alloy tubing in two alloys, Ta-10W and T-222 (Ta-9.6W-2.4HF-.01C) to each of three sizes; .500-inch OD by .062-inch wall, .375-inch OD by .062-inch wall, and .250-inch OD by .020-inch wall. The extrusion method was selected as the most economical and practical approach to producing tube hollows for subsequent tube reducing and drawing. Both the Ta-10W and T-222 alloys were extruded to 2.062-inch OD by 1.440-inch ID tube hollows from a 5-inch liner system on a 2200-ton extrusion press. Short billets of the Ta-10W alloy were successfully extruded unclad from a temperature of 2800F. Because of the additional frictional forces present, a temperature of 2800F. Because of the additional frictional forces present, a temperature of 3100F was required for longer billets. Because initial extrusions of the T-222 alloy indicated that this alloy required considerably more pressure to extrude, a molybdenum cladding technique was utilized to reduce pressures and enable us to extrude from lower temperatures. Excellent extrusions of the T-222 alloy were made using this technique from a temperature of 3000F. The main problem is in post extrusion conditioning. The tubes were roll straightened cold and conditioned by OD centerless grinding and ID boring. Many stress corrosion type cracks developed during this stage of processing. The material should be annealed or at least stress relieved between extrusion and the various conditioning operations to avoid stress cracking and extreme care should be taken in selecting coolants and lubricants.

The conditioned tube hollows were then tube reduced to 7/8-inch OD by .109-inch wall in two steps and then cold drawn to each of the finished sizes in each of five temper conditions; 1/4 hard, 1/2 hard, full hard, full hard + stress relieved, and fully annealed. Both alloys displayed good drawability with area reductions up to 62 percent without intermediate annealing. It was demonstrated that the T-222 alloy can be processed through the same schedule as Ta-10W and provide comparable results in the finished tubing. The tubing was evaluated in terms of all the routine non-destructive and destructive tests. Flaring, flattening, bend and tensile tests indicated that both alloys exhibit good ductility for their respective strength levels even with some degree of cold work. Extensive tensile and stress rupture tests were conducted at temperatures of 2100F, 2400F and 2700F. In both alloys the best combination of strength and ductility at 2400F was obtained by material in the stress relieved condition. The properties obtained for stress relieved Ta-10W were ultimate tensile strength 45 to 49 ksi, .2% yield strength 27 to 37 ksi, % elongation 20 to 25. The properties obtained for the stress relieved T-222 alloy were ultimate tensile strength 56 to 63, .2% yield strength 44 to 50 ksi, % elongation 30 to 79. In general, the strengths obtained with the T-222 alloy were 15 to 20 ksi higher than the Ta-10W, while elongations are comparable. Tubing from both alloys was successfully welded in an inert atmosphere using a tungsten electrode. While strengths were comparable to those obtained on the base metal, ductility of the welds was considerably lower than that of the base meta.

To demonstrate reproducibility of the process, a second lot of tubing in each alloy was processed to each of the three finished sizes and finished in the stress relieved condition. The tubing produced during this phase was checked for dimensional tolerances and spot checked for elevated temperatuer tensile and stress rupture properties at 2400F. Excellent correlation was obtained with the properties obtained on the test lot sequence tubes.


Provenance:
Lockheed Martin Missiles & Fire Control
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