Transformation defects on θ′ precipitates in Al–Cu alloys

Abstract

Growth defects in the form of transformation disconnections (TDs) are considered for the precipitation of 0 in an Al-Cu solid solution. The minimum sized TDs are predicted to be 1-2 nm in height, in agreement with experimental observations. One type of TD is glissile and the other (more prevalent) type is sessile, requiring climb for motion. The presence of a fault plane on one side of the sessile TD does not impede its formation. The results are in accord with symmetry theory and with the topological model for precipitation.

An atomistic simulation study of the crystallographic orientation relationships during the austenite to ferrite transformation in pure Fe

“…Hence, the B F c 1 interface will maintain a curved shape with terrace planes normal to the direction v t (figure 4(b)). A similar lateral motion mechanism has been discussed in different solid state phase transformations [57,[59][60][61]. It should be noted however, that in this particular instance, even though the α-nucleus B 1 formed different ORs with its upper and lower γ matrices, both of the interphase boundaries required the coherent plane { } { } γ α 1 1 1 // 1 1 0 to perform the ledge growth mechanism.…”

The β→α phase transformation in plutonium

“…12. Such a scheme has been proposed by Purdy and Hirth [40] for h 0 precipitates in AlCu alloys and by Heinz et al [41] for Sb 2 Te 3 precipitates in PbTe. The step heights in the present case are somewhat larger, but the principle is the same.…”

“…The step heights in the present case are somewhat larger, but the principle is the same. The method of Purdy and Hirth [40] gives the coherency strain on the step where m layers meet n layers as:…”

Disconnections in simple and complex structures

“…Perfect disconnections separating rotated interface structures like that depicted in figure 2 have been studied experimentally in NiSi 2 :Si [18] and 0 -CuAl 2 :Al(Cu) alloys [19]. Figure 4a shows the unit cell of tetragonal 0 -CuAl 2 ; the 4 2 axis is parallel to [001] and inter-relates the Cu layers parallel to (001).…”