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The formation of stacking faults upon aging a solution treated and quenched nickel-base alloy has been reported previously. More recent work has revealed a similar behavior in several γ’ precipitation hardened nickel-base alloys aged in the temperature range l400°-1650°F. The faults intersect both γ (nickel solid solution) and γ’ (Ni3Al solid solution) phases, and are of extrinsic type. Fault formation is attributed to a chemical segregation effect involving the climb of Frank partials, similar to that reported for austenitic steels.Fig. 1 shows extrinsic faults associated with a slip band in Udimet 700 lightly deformed at 70°F prior to aging. For the specified [011] normal to the foil, the slip trace is (11), and the faults lie in (111) and (11). Using the g · b = 0 or ± 1/3 (s = 0) criterion for dislocation invisibility, Figs, 1 (a-c) show that the outer partial for a (111) fault must be 1/6 [11] Shockley, or 1/3 [111] Frank.

The slip modes in the CsCl type lattice (AB structure) have been considered in detail. Glide on {100} <100> does not involve A.P.B. formation or the creation of stacking faults. In contrast glide on {110} involves displacements that create stacking faults with either <100>, <110> or <111> glide vectors; in addition A.P.B.'s are also formed by ao <110> and ao <111> dislocations. We now consider A2(BC) ternary alloys based on the CsCl lattice where additional ordering of B and C atoms occurs on one of the sub-lattices. Fig. 1 shows a {110} plane where C' is a C-type atom in a subsequent layer. It is evident that both a unit ao [010] and ao [111] translation produce “wrong bonds.” Thus glide in these directions in an A2(BC) alloy must involve either 2ao [010] or 2ao [111] superdislocation pairs. Consequently glide on these systems will be intrinsically more difficult than in a binary alloy where B and C atoms are of the same specie. Since ao <101> is still a unit translation vector in the A2(BC) lattice one would anticipate that {101} <101> slip would not be appreciably more difficult than in the CsCl type lattice.

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