Structure Of Tilt Grain Boundaries Research Articles

Atomic and Electronic Structures of Tilt Grain Boundaries in BCC Transition Metals

A tight-binding type electronic theory is used to calculate the configurational and electronic structures of coincidence-related tilt grain boundaries in bcc transition metals α-Fe, Mo and W. To obtain the atomic configurations near the grain boundaries, both electronic (d-band) and repulsive energies are calculated and minimized: The change in the d-band energy Δ E d is obtained using the second moment Gaussian approximation for the d-density of states (DOS), while the Born-Mayer potential is used to estimate the change in the short-range repulsive energies. It is shown that the grain boundary structures depend sensitively on the species of transition metals, and the asymmetric grain boundaries can be stabilized for certain transition metals. We also present the local DOS of d-electrons, calculated using the recursion method, on the atomic sites near the tilt grain boundaries.

Structure of tilt grain boundaries in b.c.c. metals

Abstract Structures and energies have been calculated for periodic, symmetrical [001] and [110] tilt boundaries in b.c.c. metals using a variety of central-force potentials. The structures were found to be independent of the potential used and in general more than one relaxed structure was found for each type of grain boundary studied. The boundary structures are analysed in terms of polyhedral groups, called compact polyhedra, with edge lengths which vary between the first- and second-nearest-neighbour separations. A smooth transition occurs between the low-angle and high-angle regimes. Relative to corresponding f.c.c. boundaries, local relaxations were found to be at least as important as rigid translations and atoms were often found to occupy coincidence sites in minimum energy b.c.c. boundaries. The symmetries of relaxed b.c.c. bicrystals were consequently found to be different, usually higher, from those for corresponding boundaries in f.c.c. bicrystals.

Structure of a Coincidence and Near-Coincidence Tilt Boundary in Gold

The structure of tilt grain boundaries formed by a rotation of 60° and 30° about a 〈111〉 axis has been examined by transmission electron microscopy. In specimens containing 30° boundaries, low-angle dislocation arrays with a tilt angle of 2.2° are commonly observed. This is attributed to the presence of a coincidence site lattice relation at 27.8°.