Corrosion of inconel 617 in HTGR grade helium
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th emery paper ( # 4 / 0 , grit size is about 15/~m) and cleaned with acetone in an ultrasonic cleaner. After being dried in vacuum, they were submitted to corrosion tests. The corrosion tests were carried out in a silica tube at 1000 ~ and atmospheric pressure for 1000 h in four helium-impurity mixture gases. A flow rate of 50 cc/min 9 cm z was maintained throughout the tests. Table II presents the chemical composition of impurities in the gases. Impurity concentration was measured at the inlet and outlet of the test apparatus by use of a hygrometer and gas chromatograph with a helium ionization detector. The oxygen and carbon potentials in these gases were calculated on the basis of equilibrium composition at 1000 ~ Figures 1 and 2 represent the plot of the_oxygen and carbon potentials against the parameter (O - C ) / S , respectively. The symbol S is S = O + H + C and O, H, and C are the number of gram atoms of oxygen, hydrogen, and carbon, respectively. The parameter (O + H + C) gives a measure of oxygen and carbon potentials. As shown in Figs. 1 and 2, 1) all of these gases have low oxygen potential so that nickel, cobalt, and molybdenum cannot be oxidized; 2) the increasing order of oxygen potential is He-4, He-2, He-l, and He-3; 3) the increasing order of carbon potential is the reverse order of oxygen potential. The results of the calculation also shows that there is little difference in the potentials between He-1 and He-2. He-1 is supposed to be the normal primary helium of H T G R which has been developed in Japan, and He-2, He-3, and He-4 represent abnormal conditions. After the corrosion tests, weight gain of the specimens was measured and the surface corrosion products were identified by X-ray diffraction. T o protect the surface scale from spalling on sectioning and polishing, the specimens were plated with copper and nickel, and the following examinations were carried out: optical metallographic observation, Electron Probe Microanalysis ( S H I M A D Z U EMX-SM7), Ion Microprobe Mass-analysis ( S H I M A D Z U - A R L , IMMA). These examinations were performed on the cross sections of the specimens. Carbon distribution on the cross sections was measured by I M M A since I M M A has higher detection sensitivity for light elements than EPMA. The details of experimental procedure on I M M A will be reported elsewhereJ 5 The depths of internal oxidation and alloying element depletion were measured from the
ISSN 0360-2133/81/0311-0451500.75/0 9 1981 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 12A, MARCH 1981--451
Table I. Chemical Composition of Inconel 617 ( W I Pct) C
Cr
Mo
A1
Ti
Fe
Co
S
Si
Mn
Ni
0.0707
20.31
8.64
0.72
0.57
1.02
11.71
0.003
0.19
0.05
balance
Table II. Chemical Composition of Impurities in the Helium Gases Used (ppm by Vol) Impurity
He- l
He-2
He-3
He-4
H20 H2 CO 2 CO CH 4 N2
0.6-0.7 432-438 0.4-0.7 250-268 2.5-4.0
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