The deformation and fracture of TiAl at elevated temperatures
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plete analysis is now available and is as follows (wt pct): Al Si Fe W Cu Mn
40.00 pct
Mo
0.010 pet
0.02 pet Zn 0.05 pet C 0.05 pet H 0.02 pet N 0.01 pet 0 Ti Balance
< 0.002 pet
0.029 pet 0.0037 pet 0.0039 pet 0.1208 pet
The ingot was homogenized at 1000°C in air for one week. The oxide was removed and the ingot completely cleaned up in a lathe. Then a further 1.9 mm was removed all over and the machining chips were dis -carde toavoid ncludinganyoxygensaturatedmaterial in the final product. The further machining chips, which in general were very fine, were saved for canning and extrusion. Prior to canning the chips were sieved and the — 30 mesh fraction used for extrusion. Cylindrical extrusion cans nominally 7.21 cm diam and 15.25 cm long were fabricated from C.P. titanium pipe with C.P. titanium ends. The cans were alternately loaded with powder and pressed to 10,000 Kg until the can was filled. The green density of the powder compact was about one-half full density. The open end of the can was welded shut and the can was then evacuated through a pipe until a vacuum of _ 1 x 10 -5 mm of Hg was attained. The pipes were then sealed, the cans covered with a glass lubricant (Fiske 604D), heated to 1415 to 1425°C, soaked for 1 h, and extruded. The extrusion ratio used was 16:1. The resulting rods were decanned in a lathe and the core material machined to rods of 9 mm diam. This material showed a grain size of about ASTM 8 (0.025 mm diam). The rods were ground in a single pass to the specimen configuration shown in Fig. 1, using a silicon carbide wheel dressed by a template (crush roller) so that the same geometry resulted each time. The flanges on the specimen allow an extensometer to be clamped on without marring the gage length surface. Strain was measured with a linear variable differential transformer (LVDT) attached outside the furnace to trailing arms extending from the specimen. The overall strain sensitivity of this system was about 2.5 x 10 -5 All tests were made in air with the specimens in the as extruded condition. Testing was performed on an Instron using a 100 pound (45.36 Kg) full scale load .
VOLUME 6A, NOVEMBER 1975-1991
to the data given, two room temperature determinations of Young's Modulus (E) and Poisson's Ratio (v) were made. In one case a rectangular compression specimen with resistance strain gages was used. This experiment yielded E = 182.5 GN/m 2 , v = 0.236. In the second experiment the moduli determined sonically
STRENGTH OF TIAL AS A FUNCTION OF TEMPERATURE
DO
-S-.-
•
Do
CA
E
Fig. 1
—
TiAI tensile specimen.
Z
°
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and a cross head speed of 0.25 mm/min (0.01 in./min) except for a few tests run at ten times that speed. Elevated temperatures were obtained with a resistance wound split furnace and temperature was maintained at t 1°C during the test. The temperature gradient over the gage length was only about 5°C at 1000°C and was presumed to be less than that at all lower temperatures. After the specimen reached the test temperature sufficient equilibrium time was allo
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