On the correlation between deformation twinning and Lüders-like deformation in an extruded Mg alloy: In situ neutron diffraction and EPSC.4 modelling

Modeling twinning and detwinning behavior of Mg alloy ZK60A during monotonic and cyclic loading

“…On the other hand, the macroscopic yielding of such textured extrusions has previously been shown via in-situ neutron diffraction and polycrystal plasticity modeling to be due to the slip of hai dislocations on prismatic planes. These prior works were performed on distinct extruded alloys, AZ31B (Agnew et al, 2006;Wang et al, 2012b) and ZM20 (Muránsky et al, 2010b), which demonstrates the broad applicability of the notion that prismatic slip is responsible for the yielding of extrusions in tension. An initial estimate for the CRSS of prismatic slip of 115 MPa is given by again assuming that the stress within the relevant grains is similar to that imposed on the aggregate (something confirmed by in-situ measurements, Agnew et al, 2014a) and invoking the Schmid factor of the majority h10.0i oriented grains, Schmid factor = 0.43.…”

“…In the former case, yielding can be rather abrupt (approaching elastic-perfectly plastic). Recent authors have associated the yield plateau observed during testing of textured Mg alloys along certain directions with Lüders banding (Muránsky et al, 2010b;Barnett et al, 2012). While the phenomenological models often capture this sharp yielding behavior, most crystal plasticity models fail to capture sharp initial yielding phenomenon.…”

Twinning-Detwinning Behavior during Cyclic Deformation of Magnesium Alloy

“…{10.2}<10.1> extension twinning is commonly found during plastic deformation at room temperature in favorably oriented grains relative to the applied loading direction, leading to tension-compression yield asymmetry and strong plastic anisotropy in magnesium alloys [5][6][7][8]. When deformation twinning occurs, the lattice is reoriented approximately 86.3° relative to the parent lattice, resulting in pronounced changes in the crystallographic texture during deformation [9][10][11][12]. In situ neutron diffraction experiments have been employed extensively to study the plastic deformation behavior of magnesium alloys.…”

Time and spatial resolution of slip and twinning in a grain embedded within a magnesium polycrystal

“…In situ neutron diffraction has been widely employed to probe the average response of similarly diffracting grains in metals yielding by twinning [3][4][5][6][7][8]. Magnesium has become somewhat of a model hexagonal close packed (hcp) material for a such study since Gharghouri et al [8] showed how changes in the diffracted intensity reveal the onset of deformation twinning and used this to demonstrate that f1 0 1 2gh 1 0 1i twinning in magnesium follows a critical resolved shear stress law.…”

“…This agrees well with the theoretical treatment by Lebensohn and Tome [9] and is an important point for the present study because resolved shear stresses can be adequately obtained from the deviatoric strains that are provided by Laue type techniques. Neutron diffraction has also been combined with crystal plasticity by a number of workers to extract effective mean critical resolved shear stresses for slip and twinning modes [4,7,10]. The stresses for the onset of twinning were found to exceed those for basal slip by a factor of 2-7.…”