Abstract Antiphase Boundaries Research Articles

Phase-Field Simulation of γ′-Co3 (Al, W) Evolution Kinetics with Antiphase Boundaries in Co-Based Monocrystal Superalloys

Antiphase boundaries (APBs) of L12 ordered γ′-Co3 (Al, W) precipitates have an essential effect on the high-temperature strength of Co-based monocrystal superalloys. In this work, the antiphase boundaries and their effects on the evolution kinetics of γ′ phase are studied with the phase-field model. The formation of APBs between γ′ phases with different crystallographic variants induces a sharp increase in free energy; the width of APBs measured by the edge-to-edge distances of the γ′ phase is consistent with the experimental results of superalloys. Also, a coupling behavior of Ostwald ripening and APB’s migration in the coarsening of the γ′ phase is revealed. In addition, the volume fraction of the γ′ phase with four antiphase domains is lower than that of the single-domain γ′ phase, and the time exponent of the particles’ number density of the γ′ phase at the steady coarsening stage changes from –0.99 of single domain to –0.8 of APBs. The results show that the high-energy APBs can reduce the coarsening rate of γ′ phases, which are significant in the microstructure and composition designing of the ordered precipitates with APBs in Co-based superalloys.

Formation, faceting, and interaction behaviors of antiphase boundaries in GaAs thin films

Antiphase boundaries occur in GaAs epilayers grown on (001) Ge substrates by organometallic vapor-phase epitaxy methods. The formation and structural characteristics of these boundaries were investigated by transmission electron microscopy (TEM). Steps with particular heights at the surface of substrates nucleate antiphase boundaries. The observed faceting behavior of these boundaries indicates that energy associated with the presence of antiphase boundaries is strongly related with the boundary planes, and preservation of the stoichiometry of GaAs appears to play an important role in achieving a lower energy state at antiphase boundaries.

Pinning mechanism of vortices at antiphase boundaries in YBaCuO films

Antiphase boundaries represent dislocation free interfaces in YBaCuO with small structural width of less than 1 nm. We show, that strong pinning at such boundaries takes places by quasiparticle scattering induced variation of the condensation energy, characteristic of superconductors with anisotropic gap. The length scale of the order parameter suppression at antiphase boundaries will be discussed.

The structure, thickness and chemistry of antiphase domain boundaries in heat-treated, rapidly solidified Ni3Al

Abstract Antiphase boundaries (APBs) in a rapidly solidified Ni3Al alloy have been examined by transmission electron microscopy in the as-solidified state and after annealing. Dark field imaging suggests that the APB thickness increases with temperature during annealing and that a dark, disordered phase appears at temperatures above about 800°C. The boundary region at high temperatures has a chemical composition close to that expected from the phase diagram for the disordered phase, namely containing about 15 at.% Al. Examination of APBs by high-resolution electron microscopy does not confirm the disorder, however, and the so-called disordered regions showing dark contrast may in fact be caused by the significantly modified chemistry of these ordered regions. It is not clear whether disorder may form at high temperature when the average alloy composition enters the two-phase ordered + disordered region, or whether simply extensive segregation takes place to the APB without the true appearance of a second,...

The role of antiphase boundary energy in influencing intergranular failure in iron aluminides

Abstract Antiphase boundaries (APBs) may lead to stress homogenization through dislocation/APB interactions and reduce the tendency for intergranular failure in ordered intermetallics. It is shown for ordered iron aluminides that these interactions are influenced by the APB energy. The interactions are maximized at intermediate (≃32 at.%) Al-contents. A high APB energy inhibits the formation of mechanical as well as thermal APBs and contributes to intergranular failure observed at high (40 at.% or more) Al-contents.

Structure and anisotropy of antiphase boundaries in rapidly solidified Ni3Al

Abstract Antiphase boundaries (APBs) were studied by transmission electron microscopy in rapidly solidified Ni3Al compounds. It is shown that the antiphase vector can be decomposed into R = R o + r. The main term R o = ½ [110] gives rise to a strong fringe pattern, of the π type, when superlattice reflections are present. A small relaxation term r, giving a faint fringe contrast when only fundamental reflections (i.e. 111) are acting, was found to be maximum when lying in the boundary plane. For a given R o, the modulus of r varies with the boundary orientation. Comparison between experimental and simulated images indicated that r is at least one order of magnitude smaller than R o. Statistical determinations of the APB orientations evinced no anisotropy in their distribution. It is concluded that r restores the isotropy of the APB energy, which is unexpected if R = R o.

Direct observation of antiphase discommensurations in TiSe2by transmission electron microscopy

Antiphase boundaries associated with the charge density wave superlattice in 1T-TiSe2 have been observed by satellite dark-field transmission electron microscopy. By analogy with 2H-TaSe2, the antiphase boundaries in TiSe2 are interpreted as antiphase discommensurations associated with a commensurability of order two.