Dynamics of twin layer broadening in indium

Abstract

IntroductionAn initial stage of the deformation twinning process, i.e. the stage of elastic change in diinensions of lens-shaped or wedge-shaped twins, has received the most study, and the detailed theory permits niany effects produced in this stage to be predicted and treated adequately indeed (KOSEVICH, BOIKO). It is substantially worse with the treatment of a subsequent growth of a twin -in length and in width. Here the situation is hardly simpler than that under slip deformation although the growth process is completely localized at twin boundaries and consists in involving next-in-turn atom planes (if one does not deal with polysynthetic twins). The experimental data accumulated permit the main factors affecting the twin broadening to be pointed, but are still insufficient for the unambiguous analysis (KLASSEN-NEKLYUDOVA; STARTSEV). S. V. LUBENETS, L. S. FOMEKFROOf the recent experimental data those are of greatest interest which have been found for calcite crystals (BENGUS et al. 1965(BENGUS et al. , 1967(BENGUS et al. , 1974SOLDATOV et a]. 1971SOLDATOV et a]. , 1973STARTSEV et al. 1974; CHAIKOVSRAYA;BENGUS 1973) deformed solely with twinning a t T 2 300 K. The authors of the above papers conclude that the mechanism of twin layer broadening is related directly to the dynamics of twinning dislocations, i.e. to their nucleation and motion along a twin boundary. For thin perfect crystals of Zn, twins have been shown (PRICE) to broaden under stresses comparable to those calculated with the assumption of thermally activated nucleation of dislocations but these stresses are appreciably higher than those in calcite and other bulk crystals. This discrepancy may be due to the fact that the latter have stress concentrators which facilitate the nucleation process of twinning dislocations (BENGUS et al. 1985(BENGUS et al. , 1967(BENGUS et al. , 1974SOLDATOV et al. 1971SOLDATOV et al. , 1973STARTSEV et al. 1974;BENGUS 1973).The other hypothesis of the nature of resistance to twin boundary motion is given (COOPER, WASHBURTJ) on the basis of studies in deformation of zinc crystals with residual twin layers. The boundary drag is said to be due to the ahead basal dislocations pushed ; the thermal activation parameters measured are attributed to the interaction between basal dislocations and crystal structure imperfections. Thus, the control mechanism for boundary motion is essentially in no direct relation to the twin boundary itself.The twin boundary motion has been calculated for the model of thermally activated nucleation of twinning dislocations as a control factor of twin broadening in a crystal perfect in some other respects (SUMINO 1966a). The twin boundary is treated as a special area of certain width which differs from the rest of the crystal in its reduced shear modulus. The relation between the boundary width and shear modulus in the area has been calculated (SUEZAWA, SUMINO) based on the ideas given by KONTOROVA. This feature of the boundary also refers to factors which facilitate the nucleation of twinni...

Energy barriers associated with slip–twin interactions

“…Twin translation with coplanar slip provides the least effective barrier to slip among all cases. We note that, all these five different dislocation-CTB reaction cases (Cases (i)-(v)) have been observed previously in experimental research [12,14,[16][17][18][19][20][21][24][25][26]30,31].…”

“…Short-range transmission on cube planes can occur when the other slip systems are not available [25][26][27][28]. In addition, the incident dislocation-CTB reactions can also trigger dislocation multiplication [10,13,18,19,29] on , T planes and twin translation [30,31] on the plane; these represent two mechanisms that are not well studied. The culmination of these cases underscores the complexity of dislocation-CTB interactions that need to be considered on a case-by-case basis.…”

“…Glide transmission follows from the reaction of trailing partial with a residual dislocation in Case (iii) [12,13,19], with elevated energy barriers for glide transmission (Figure 2d), as we will see later. In addition to the aforementioned reactions, CTB translations can occur (Case (iv), Figure 2e), which move the upper and lower twin-matrix interfaces in the transverse direction [30][31][32][33][34][35]. An important ramification of the incorporation and transmission processes is that several dislocation multiplication (nucleation) events can occur at the interaction site [10,13,18,19,29] (Case (v), Figure 2f ).…”

Dynamics of twinning in metals and alloys

“…Let us first consider the pole mechanism. I n indium [90] the twin boundaries move under shock loading very rapidly. Thus, for z, = 3.35 MPa, one finds 8, = 6.4 x lo3 cm/s.…”