Segregation, precipitation and wetting of tilt grain boundaries in molybdenum

The intrinsic structure of different tilt grain boundaries in bcc molybdenum is determined by electron microscopy and compared to the ones obtained after an annealing treatment of the same boundaries in presence of different impurities like carbon and nickel. Specially grown bicrystals with tilt axes parallel to [ 001] and [ 011] are used. The boundaries correspond to the major coincidence relationships Sigma = 5, Sigma = 3 and Sigma = 11. Their experimental atomic structure is compared to calculated ones. After the treatments in presence of carbon or nickel the new structure is determined by electron microscopy from the structural and chemical aspect. After a treatment in presence of carbon the Sigma = 5[001]{310} boundary contains either a segregation or a very thin precipitate layer of a new MoCx quadratic phase. In presence of nickel, the physical phenomenon is possibly a wetting of the boundary. The different [011] tilt boundaries have a different behavior according to their respective energy.