  Slip transfer at grain boundaries and annealing twin boundaries was studied
in polycrystalline Ni by means of slip trace analysis. Slip transfer or
blocking was assessed in $>$ 200 boundaries and was related with geometrical
criteria that establish the alignment between the active slip systems across
the boundaries. It was found that slip transfer mainly occurs at low-angle
regular grain boundaries and that a Luster-Morris parameter $>$ 0.8 stands for
the best criterion to assess slip transfer. In the case of coherent or
incoherent twin boundaries, slip transfer occurs when the residual Burgers
vector is close to zero through dislocation cross-slip.
