INFLUENCE OF GRAIN-SIZE AND TEXTURE ON THE CYCLIC STRESS-STRAIN RESPONSE OF NICKEL

The cyclic stress-strain behavior of fine-grain (24 mum) nickel was co mpared with previously published results on coarse-grain (290 mum) nic kel to evaluate the effects of grain size on cyclic hardening. The fin e-grain nickel exhibited a moderate [111][100] fiber texture, while th e coarse-grain material was essentially texture free. As a result, tex ture also influenced the cyclic responses. Fatigue experiments were co nducted at plastic strain amplitudes ranging from 2.5 x 10(-5) to 2.5 x 10(-3). At a plastic strain amplitude of 2.5 x 10(-5), the cyclic re sponses of the two types of materials were nearly identical. Above tha t plastic strain amplitude the fine-grain-textured specimens exhibited higher saturation stresses. The difference became greater as the plas tic strain amplitude increased. The higher saturation stress in the fi ne-grain-textured material was primarily caused by a higher back stres s. Both grain sizes exhibited cyclic stress-strain curve plateaux exte nding from plastic strain amplitudes of 2 x 10(-4) to 8 x 10(-4). The results are discussed in terms of traditional monotonic Hall-Petch mec hanisms and the cyclic stress-strain behavior of multiple-and single-s lip-oriented single crystals.