The effect of high pressure hydrogen gas on the mechanical properties of three Ni based eutectic composites
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focused on the effects of hydrogen on the m a t r i x / r e inforcement interface.
EXPERIMENTAL PROCEDURE Eutectic alloys were m e l t e d f r o m 99.97 pet purity Ni, 99.999 pet purity Al and Nb, and 99.9 pct purity Cr. The compositions produced were Ni-45.5W, Ni19.TNb-6.0Cr-2.5AI, and Ni-21.75Nb-2.55A1. (All compositions are given in weight percents.) Melts of approximately 1500 g total weight were made in alumina crucibles under flowing argon atmospheres. The alloys were melted, held at a temperature approximately 150 K above the melting point for 30 rain, and poured into cylindrical copper chill molds. The resulting ingots were 1.5 cm in diam and approximately 20 cm long. Chemical analysis of several preliminary heats showed that there was little change in composition during the melting. After cooling, the eutectic rods were removed from the chill mold~ cleaned, inserted into alumina tubes surrounded by graphite susceptors, and directionally solidified by moving them through a five-turn induction coil at a rate of 3.7 cm per h. The directional solidication was performed in vacuum for the Ni-W and in flowing argon gas for the other compositions. Samples for metallography were taken, and a uniform eutectic structure free of cells was found in the central 16 to 18 cm of each ingot. From each ingot two specimens were machined. These specimens were of the smooth and notched types shownin Fig. 1. The specimens were pulled to failure in either 34.5 MN/mz hydrogen or 34.5 MN/ m2 helium gas at a displacement rate of 0.02 rain"I. The test chamber was first flushed with the gas to be used, then evacuated to diffusion pump vacuum, refilled and pressurized. The test was then commenced immediately. An extensometer capable of VOLUME 8A, APRIL 1977-535
5/16-24 N.F. threads Table I. Mechanical Properties o f Ni-45.5W
F
0 rll L
6.4
] IllilllID
.I
___•-7.9 Gas
l
23.9----~ I-
H2 He
3 2
535.0 515.7
H2 He
3 2
-
772.2 859.8
739.8 1172.1
Table I1. Mechanical Properties o f
trlri,l i$
Number of Tests 85.8
Reduction in Area, Pct
30.4 46.8
30.7 73.3
-
2.6 34.7
___~- 7.8
9 -
Elongation, Pct
Notched Bars
Root dia. 5.6 / a p ~ O ~ ° t r a d i u s 0-05
19q,2!RIlll'llllltl
Ultimate Tensile Strength, Mn/m~ Smooth Bars
85.8
5/16-24 N.F. threads \
I
Number of Tests
0.2 Pct Yield Strength, Mn/m2
0.2 Pet Yield Strength, Mn/m2
-I
Ni-lg.7Nb.6.0Cr-2.SAI
Ultimate Tensile Strength, Mn/mz
Elongation, Pct
Reduction in Area, Pct
0.3 3.1
0.5 5.9
Smooth Bars
F i g . 1--Drawings of smooth and notched t e n s i l e b a r s u s e d t o investigate hydrogen d a m a g e susceptibility, Dimensions in millimeters.
H~ He
2 2
896.3 990.0
r e c o r d i n g t h e f i r s t 5 p c t o f t h e d e f o r m a t i o n was u s e d on a l l s m o o t h s p e c i m e n s .
H2
2
-
He
2
900.4 1059.7 Notched Bars
549.5
-
0
907.3
-
0.4
RESULTS Tensile Properties The average mechanical properties measured in hydrogen and helium for the three alloy compositions are given in Tables I to III. For the relatively ductile
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