Atomic Transfer in Inconel 617 due to High Temperature Corrosion in Impure Helium
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Fig. 1--Schematic representation of corrosion products.
Fig. 2--Line profiles of Si, Mo, AI, Ti and C. The profiles were obtained by using IMMA. behavior can be illustrated by considering the phenomenological diffusion equations. 5,6 The diffusion flux of c o m p o n e n t i in alloy relative to a fixed lattice f r a m e work, j,, is written n-1
MASAHIRO KITAJIMA is Researcher, and MASATOSHI OKADA is Chief of Second Laboratory, Nuclear Material Division, National Research Institute for Metals, Tsukuba Laboratories, Sakura-Mura, Ibaraki 305, Japan. Manuscript submitted September 10, 1980. 1144--VOLUME 12A, JUNE 1981
J, = -
~., L,kdl~kldx
[1]
k
where, n is the number of c o m p o n e n t which contains dissolved oxygen and carbon, L~k is the
ISSN 0360-2133/ 81/ 0611-1144500.75 / 0 9 1981 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
METALLURGICALTRANSACTIONSA
phenomenological coefficient which means the interaction between i and k, and d g f l d x is the chemical potential gradiant of component k. It is general that the most immobile component has been used as a lattice frame work: v,s Ni, Fe or Cr. Consider from the microscopical analyses that no other elements other than Si, Mo, A1, and Ti contribute to oxidation and carburization, i.e. their interactions with oxygen and carbon are negligibly small. The Eq. [1] can be rewritten as
J, = - ~ L,gt#k/dx
[2]
k
k -- C, O, Si, Mo, A1, and Ti. Since silicon and molybdenum oxides, and aluminum and titanium carbides were not observed, the interactions Ls~o, Luoo, LAJc, and L~ c are considered to be sufficiently small. Furthermore, if the interactions between metal atoms concerned with corrosion such as L~os,, or LMoA~ are also neglected, the diffusion flux of metal is expressed from Eq. [2]
JM
=
-LMzdgz I dX-LMMdg M/ dx
[31
M = Si, Mo, A1 and Ti; Z = C for Si, Mo, and O for A1, Ti. Now we define the carburization zone and the oxidation zone where formed carbides and oxides are embedded in the matrix. A similar zone for the theory of the internal oxidation of alloys had been proposed. 9 The diffusion is governed by carbon and oxygen dissolved from the gas phase into those corrosion zones in alloy. When the reaction between metal atom M and nonmetallic atom Z to form carbide or oxide M~Z is considered, gMvZ m Pls
"~ IXZ '
[5]
considering activity of M~Z 1 independent of x. By using the relation [5], Eq. [3] is rewritten as
JM = (--LMM + VLMz) ( - d ~ z / vdx)
[6]
Goto et al s have used the relation of L,k with diffusion coefficient D,k
D,k = L,kdgk / dCk
[71
in study of transport phenomena in the multicomponent ionic solution, where Cg is the concentration of species k. In Eq. [7], the cross terms of the " G - m a t r i x " have been neglected; the more exact form is written in Appendix I. We obtain the next equations by use of Eq. [7],
JM = J, + J2
d # z / d x = A# z/AXz = (~,i - ~,~)/ax~,
total quantity = - i (C,(x) - C,)dx,
[8] Table I (a). Fluxes of Mo, S|, AI and T|
J~ = -DMMdCi/d#M(-d#z/vdx) = - ( R T)-IDMMdCM I din a
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