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a b s t r a c tThe influence of spatial variability of the crystal stresses on the evolution of intragrain lattice misorientations during cyclic loading of a polycrystalline copper alloy is examined using a combination of simulation and experiment. The experiments consist of measuring the mechanical responses of deforming individual crystals using high-energy x-ray diffraction and in situ mechanical loading. The simulations employ a crystal-based finite element formulation which is used to compute stress distributions and lattice reorientations in virtual polycrystals subjected to the same loading history. The hybrid methodology produces a picture of the evolving microstructural state during cyclic plasticity. For four target grains, comparisons are made between the diffracted peak intensity distributions as recorded by the experimental detector and those computed from simulation using a virtual diffractometer. Based on the comparisons, a relationship is presented between intragrain lattice misorientations and broadening of the diffraction peaks from individual grains. Stress triaxiality within grains is examined and regions with positive triaxiality throughout the tension/compression loading history are identified as potential locations for void growth.

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The authors report on a relatively new alloy, Ni54Ti45Hf1, that exhibits strengths more than 40% greater than those of conventional NiTi‐based shape memory alloys − 2.5 GPa in compression and 1.9 GPa in torsion − and retains those strengths during cycling. Furthermore, the superelastic hysteresis is very small and stable with cycling. Aging treatments are used to induce a very high density of Ni4Ti3 precipitates, which impede plasticity during cycling yet do not impart substantial dissipation to the reversibility of the phase transformation. Pairing compression testing with high‐energy synchrotron X‐ray diffraction and aberration‐corrected electron microscopy provides an in‐depth look at the structure‐property relationships of this alloy. Specifically, it is found that a combination of small, untwinned retained martensite laths, and dislocations on the austenite‐martensite interfaces primarily strengthen the alloy as opposed to dislocation networks. Furthermore, some combination of nanoprecipitation and interface dislocations is responsible for the remarkably low mechanical hysteresis exhibited by this material.

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