The Slip Modes in Alloys with the A2 (BC) Heusler-Type Structure

Abstract

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.