Thermal disordering near a ?=3{111} twin boundary in Cu3Au

Abstract

Symmetrical and asymmetrical configurations of a 2? = 3 (111) twin boundary in Cu3Au are studied by means of energy minimization and Monte Carlo simulations of a rigid lattice, using an adapted n-body potential. We find that relaxation occurring in the neighborhood of the boundary is larger for asymmetrical than for the symmetrical minimum energy configurations. From energy minimization the latter are also shown to correspond to the lowest excess energy. For the asymmetrical twin structure, Monte Carlo calculations of the long-range order parameter on a local basis show the existence of prewetting effects, i.e., the appearance well below the critical temperature of several partially disordered layers at each side of the twin boundary. In contrast, the order is preserved in the symmetrical twin in the same temperature range. These results are consistent with experimental observations of wetting in 2? = 3 (111) twins in Cu3Au, and it is found to occur at lower temperature in asymmetrical than in symmetrical boundaries.

Temperature dependencies of the relaxation, order and segregation at a tilt grain boundary in

“…The interplanar spacing ( d/d) (210) for Cu-Au planes close to the boundary plane was determined from the HREM simulated image [21]. A good agreement is found with the present energy-minimization results.…”

“…At 0.25 T c , these planes are 90% gold. This contrasts with the case of the = 5 (100) (reference [25]) and the = 3 (111) (reference [26]) boundaries for which neither significant segregation nor relaxation is found.…”

“…This order parameter is identical to that used in the mean-field theory as applied to the study of alloy surfaces [23]. [21]. Among all possible variants, the configuration S 51 shown in figure 1 has the lowest excess energy.…”

“…The boundary planes have either pure copper or mixed Cu-Au composition [19,20]. Among the possible variants, we selected that observed by HREM and denoted as S 51 in [21]. As shown in figure 1, the boundary plane is of mixed composition.…”

[001] Twist boundaries in Cu3Au for T ? 0 K

“…It was found that there is a sequence of firstorder transitions which correspond to the successive disordering of pairs of planes parallel to the interface. More recently the S = 3 [111] twins were studied in the context of the rigid lattice Monte Carlo method and an N-body potential [23]. It was found, by performing molecular statics, that the strains at 0 K are localized around the coherent twin boundary.…”