Effect of Grain Boundaries on Yield Drop Caused by Short-Range Order in .ALPHA.-CuAl Alloys.

The purpose of this investigation was to elucidate the effect of grain boundaries on yield drop caused by short-range order in α-CuAl alloys. Bicrystals with Σ3 {111} boundaries (coherent twin boundaries) of Cu-3 at.% Al and Cu-9 at.% Al alloys were grown by the Bridgman method. Bicrystal and single crystal specimens with different orientations were cut from the bicrystals. Difference in deformation behavior at room temperature among the specimens were compared by tensile tests. When the grain boundaries in the bicrystal specimens were obstacles to the motion of dislocations on the primary slip planes, the yield drop observed in α-CuAl alloy single crystals vanished or diminished. Changes in flow stresses due to the Σ3 {111} boundaries were shown. The contribution of the Σ3 {111} boundaries to the strength of the alloys and its aluminum concentration dependence were discussed.