Structure of interphase boundaries in a Eutectic Co-Al alloy
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Communications Structure of Interphase Boundaries in a Eutectic Co-AI Alloy A. GUHA, H . I . AARONSON, and W. A. T. CLARK A number of experimental 1-9 and theoretical 1'1~ studies have been reported on the structure of partially coherent fcc:bcc boundaries formed by crystals which are disordered solid solutions of either substitutional 1-4'7's or interstitial 6 type. The present investigation examined the effect upon this structure of introducing long-range order in the bcc phase. A directionally solidified Co-rich Co-AI eutectic alloy, consisting of faceted rods of CsCl-ordered bcc CoAl embedded in disordered fcc Co-rich Co-A1 solid solution (hereafter termed "Co"), was used for this purpose. An ingot prepared by combining 99.995 pct Co and 99.995 pct A1 in eutectic proportions (9.52 wt pct AI ls'19) was remelted in an A1203 crucible under a flowing argon atmosphere. Withdrawal at 10 -2 m per hour through a water cooled Cu block yielded a directionally aligned eutectic structure. Sections cut parallel to the growth (and rod axis) direction were annealed at 1150 ~ for four hours in evacuated quartz capsules and then water quenched in order to eliminate precipitation within the two phases and retain the fcc structure of "Co". Final thinning of specimens for Table I.
*When forecasting the visibility of the linear defects, the influence of the dilatation normal to the line direction, i.e., the g 9 b x u term, was computed; these results, however, are not included in the table.
values for the shortest crystal lattice translation vectors in the fcc and bcc lattices are also given in this table. Comparison of the observed and calculated contrast indicates that for set no. 1 the Burgers vectors may be described either as a[1T0],,co,, or a[100]CoAl and for set no. 2 a[0111],,Co,: or a[111]CoAl. The length of the first, third, and fourth of these vectors has been doubled, relative to their values in Table I, in order to take into account the CsCl-ordering of the CoAl
Calculated g 9 b Values and Observed Contrast for Boundary of Figures 1 and 2
"Co" Reflections Set Number g/b
111 111 020 200 511 151
a/[llO] 2 0 2 2 4 4
a/[lO]] 0 2 0 2 4 0
a/2[Ol]-] 1 1 1 0 0 2
a/[110] 0 2 2 2 4 4
a/[lO1] 2 0 0 2 4 2
a[O11] 0 0 1 0 2 2
1 s/w w s s s s
2 s/w s s w w s
CoAl Reflections Set Number a/Jill] 101 2 OTI 0 110 2 200 2 w = weak; s = strong g/b
a/[l]l] 0 2 2 2
a/[O01] 1 1 0 0
a/[lll] 0 0 0 2
A. GUHA. formerly a Postdoctoral Research Associate with the Department of Metallurgical Engineering, Michigan Technological University, Houghton, M1, is now Senior Metallurgist, Alloy Research and Development, Brush Wellman Inc., 17876 St. Clair Avenue, Cleveland, OH 44110. H.I. AARONSON, formerly Professor in the Department of Metallurgical Engineering, Michigan Technological University, Houghton, MI, is now R. E Mehl Professor, Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213. W. A.T. CLARK, formerly a Postdoctoral Research Associate with the Department of Metallurgi
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