Application of secondary ion mass spectrometry to the study of carburization of superalloy
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data on microanalysis of carbon. The chemical analysis is not a suitable method for microanalysis. The sensitivity of X M A is low for carbon. Autoradiography has been used to obtain direct evidence for microscopic carbon segregation. 6,~2This analytical technique, however, suffers from some obvious drawbacks in the study of carburization in gas as in this work: the composition and chemical state of alloying elements cannot be determined and the analytical technique is comparatively troublesome. I M M A is one of the more suitable instruments for microanalysis of carbon, since it has the advantage of high sensitivity for small mass elements as mentioned above. In this work, we studied microscopically the carburization behavior of Inconel 617 corroded in impure helium gas with high carburizing potential by use of IMMA. Chemical states of the precipitates produced by the corrosion were determined by X-ray emission spectra.
2. E X P E R I M E N T A L P R O C E D U R E A Shimadzu-ARL IMMA was used in this work. The instrument has oil free sections--namely two sorption pumps and an ion pump. Thus, surface contamination from pump oil can be avoided. In the A R L type instrument, the primary ion beam is mass-analyzed to select primary ions, and the beam can be focused to a probe diameter from ~ 2 to 300/~m. The mass spectrometer is a high transmission stigmatic-imaging doublefocusing instrument of moderate mass resolution. Analyses were made mainly by using 20 KeV O2and N~primary ion beams, about 5 ~m in diam, that were rastered over an area 150/~m by 300/~m and linescanned from the surface to a depth of about 1000/~m. Since the ion yield of carbon is not high, sufficient beam current was necessary for analysis of carbon: the beam current was about 4nA with a diam of 5/~m. The beam of N~ion was used mainly for the oxide scales.
ISSN 0360-2133/80/1013-1645500.75/0 METALLURGICAL TRANSACTIONS A 9 1980 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 11A, OCTOBER 1980--1645
The analyses were carried out over a cross section of the specimen, because the corroded layer was too thick to analyze the precise depth profile. The measurement was carried out after presputtering cleaning of the sample for several minutes. Shimadzu EMX-SM type XMA was used for analysis of chemical states of elements in scale and precipitates. The XMA-analyses by the X-ray emission spectra were carried out over the cross section. An electron beam of 10/~m in diam and 0.2 nA was used. The intensity of X-ray emission spectra was point-counted. T o impi'ove the sensitivity, data were integrated for 40 s for each step. Wavelength shifts of X-ray emission spectra were measured with an error of 0.003 ~ 0 . 0 1 L 8 Comparisons of spectra of the specimen with those of a standard sample were carried out. Sample p r e p a r a t i o n - - T h e chemical compositions of Inconel 617 used as the test material and impurities in helium gas are given in Table Ia and lb. The specimen of 5 mm • 8 mm • 2 mm was corroded in impure helium environm
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