Effect of phase morphologies on the mechanical properties of babbitt-bronze composite interfaces
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INTRODUCTION
B E C A U S E of the desirable strength properties of composite materials, it has become increasingly important to develop nondestructive evaluation (NDE) techniques for assessing the structural behavior of composite interfaces. Nevertheless, little information is available regarding the relationship between material strength and NDE of composite interfaces. Thus, previous work was conducted on a babbitt-bronze interface to test the ability of ultrasonic methods in this regard, t~] It was observed that a high ultrasonic reflection percentage correlated with low strength, low ductility, and a low percentage of bonded area. These results, however, were based on a composite gland seal ring composed of babbitt metal containing more copper than currently used. Because of the importance of these rings in preventing leakage of hydrogen gas from the rotor of steam generators, it is desirable to know whether these same correlations hold for babbitt metal containing less copper. Note that in steam generators, hydrogen gas is often used as a coolant. Consequently, this study compared the mechanical and ultrasonic properties of the two composite interfaces with different copper contents in the babbitt metal. In addition, the microstructural characteristics at the babbittbronze interface were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron microprobe analysis. This information was used to gain a better understanding of the interfacial fracture mechanisms. Moreover, the effect of phase morphology on interfacial strength was emphasized in the present study. P.K. LIAW, Fellow Engineer, and M.N. GUNGOR, Senior Engineer, are with the Westinghouse Science and Technology Center, Pittsburgh, PA 15235. Y. IJIRI, Student, is with the Department of Physics, Princeton University, Princeton, NJ 08544. B.J. TASZAREK, Senior Engineer, is with the Westinghouse Machinery Technology Division, Large, PA 15236. S. FROHLICH, formerly with the Westinghouse Power Systems Operations Division, is a consultant, 1231 Dermiston Avenue, Pittsburgh, PA 15217. W.A. LOGSDON, the Reverend, formerly with the Westinghouse Science and Technology Center, resides at RD #1, Box 279C, Lyons Run Road, Trafford, PA 15085. Manuscript submitted March 13, 1989. METALLURGICALTRANSACTIONSA
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MATERIAL
All experimental work was conducted on composite gland seal rings made of an inner babbitt metal layer and an outer bronze layer. The width of the bronze portion was 4.0 cm, while that of the babbitt section was 1.5 cm. The gland seal had an inner diameter (ID) of 31 cm, an outer diameter (OD) of 42 cm, and a thickness of 5.1 cm. The bronze portion of both gland seal rings was centrifugally cast and was layered with a small amount of tin-lead alloy. This pretinning alloy was deposited on the bronze at 360 ~ for 12 minutes. Melted babbitt metal (at 474 ~ was then poured over the pretinned bronze and cast into the composite ring. A completed ring and a cross-sectional view are illustrated in Figures 1
