SEGREGATION TO AND STRUCTURE OF [001] TWIST GRAIN-BOUNDARIES IN CU-NI ALLOYS

The segregation, thermodynamic, and structural properties of [001] twist boundaries in Cu-Ni alloys have been examined within a wide range of misorientations and temperatures. Cu always segregates to the boundary. The concentration of the first layer adjacent to the boundary increases monotonically with misorientation and no obvious cusps are observed. All other thermodynamic properties vary smoothly with the misorientation, with the exception of the vibrational entropy of the boundaries without segregation. The unsegregated vibrational entropy shows a large peak at the misorientation corresponding to the SIGMA17 boundary and two minima around the SIGMA13 and SIGMA5 boundary orientations. The concentration distribution within the plane of the grain boundaries can be described by the same structural unit model established for [001] twist boundaries in pure materials. Regions of large tensile stress show greater segregation than do regions of compressive stress. Regions of large shear stress tend to show reduced segregation compared with regions of small shear stress.