Mechanical behaviour of Σ3 boundaries in Ni3Al Original Research Article

The mechanical properties of Σ3 boundaries in binary stoichiometric Ni3Al were studied by performing tensile tests on miniature bicrystal specimens. It was found that Σ3 boundaries do not fracture in air. They are intrinsically strong and show no environmental embrittlement, independent of the grain boundary plane. An upper angular deviation limit, Δθc = 15Σ-1 ~ 15Σ-2/3, is suggested for the Σ3 boundary depending on the fracture behaviour. The boundaries lying within Δθc do not fracture, whereas the boundary with an angular deviation larger than Δθc exhibits brittle fracture. The macroscopic slip behaviour at the grain boundary was found to be related to specimen geometry. when the common slip system in both halves of the bicrystal is the primary slip system, slip can transfer readily across the grain boundary, leading to uniform deformation. Otherwise, slip is impeded at the grain boundary.