The Influence of Grain Boundary Phosphorus Concentration on Liquid Metal and Hydrogen Embrittlement of Monel 400
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I.
INTRODUCTION
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M A T E R I A L susceptibility to intergranular liquid metal embrittlement (LME) and hydrogen embrittlement (HE) is strongly influenced by grain boundary chemical composition. In general, high concentrations of solutes which embrittle the grain boundary should be avoided since they increase sensitivity to HE and LME. For example, HE is increased by the segregation of temper embrittling elements in steel, 1 and by tin, antimony, 2 and sulfur 3'4'5 in nickel. The susceptibility of Hastelloy C-273, an age hardening nickel alloy, to HE is reportedly increased by segregation of phosphorus 6'7 and sulfur 7 to grain boundaries. The segregation of tin and lead in steel increases embrittlement by liquid lead. 8 Other studies suggest that the segregation of certain solutes may reduce embrittlement. Dinda and Warke s report that the addition of phosphorus and arsenic to steel reduces LME by lead; and Costas 9 reports that mercury LME of copper-nickel alloys (10 to 67 pct nickel) is reduced by small additions of phosphorus. The absence of detectable precipitation and the enhancement of the effect by slow cooling suggest that a modification of grain boundary composition is involved. In a study of HE of nickel, Bruemmer e t al 4 report a decrease in embrittlement as grain boundary phosphorus concentration increases. The reduced embrittlement is attributed to a reduced tendency for sulfur to segregate in the presence of phosphorus. The objective of the present study was to investigate the effect of a potentially beneficial grain boundary segregant on both LME and HE. This was accomplished by determining the influence of a well characterized modification in grain boundary chemistry on both forms of embrittlement. Monel | was selected for study. It is a single phase, solid |
trademarkof the International Nickel Company, Inc.
solution strengthened nickel base alloy with copper as the major alloying element.
A.W. FUNKENBUSCH, formerly Graduate Student. Department of Metallurgical Engineering, Michigan TechnologicalUniversity, is now at United TechnologiesResearch Center, East Hartford. CT 06108 and L. A. HELDT and D.F. STEIN are at Michigan Technological University, Houghton, MI 49931. Manuscript submittedFebruary23, 1981. METALLURGICALTRANSACTIONSA
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PROCEDURE
The as-received material was commercial warm rolled sheet 0.635 cm thick with composition as shown in Table I. The sheet was cold rolled to 0.13 cm thickness using repeated reductions of 0.025 cm. Samples for subsequent metallography, rectangular Auger bars, and tensile samples having 0.95 cm gage length and cross section 0.13 cm x 0.32 cm were cut from the sheet with their long axes parallel to the rolling direction. The Auger bars were notched with a file, and all samples were hand polished with 600 grade SiC paper. After cleaning in reagent grade acetone, the samples were encapsulated in quartz at a pressure of 1.3 Pa. The capsules were heated to 900 ~ over a .u.u.~.c.- m. ., u. ,. . . . . pef~od, h . .1A . . .at999 . . . . . . . . or, . . . .fo
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