Strain rate and temperature effects on the selection of primary and secondary slip and twinning systems in HCP Zr

Abstract

We investigate the temperature and rate dependence of slip, twinning, and secondary twinning in high-purity hexagonal close packed a-Zr over a wide range of temperatures and strain rates (from 76 K to 673 K and 0.001 s À1 to 4500 s À1 ). To reliably identify the dominant deformation mechanisms for each condition, we employ electron-backscattered diffraction (EBSD), dislocation theory, multi-scale polycrystal constitutive modeling, and a thermally activated dislocation density evolution based hardening law. We demonstrate with direct comparison with measurement that the constitutive model, with a single set of intrinsic material parameters, can predict the underlying texture evolution, primary and secondary slip and twin activity, and twin volume fraction associated with the different loading orientations and applied temperatures and strain rates. We find that the f1 0 1 2gh1 0 1 1i twin is the preferred tension twin, either as a primary or secondary twin depending on the sample orientation, over the broad temperature and strain rate range tested. In contrast, we show that the preferred contraction twin, whether f1 1 2 2gh1 1 2 3i or f1 0 1 1gh1 0 1 2i, is sensitive to temperature but insensitive to strain rate and whether it is a primary or secondary twin. Based on the concomitant changes in the dominant slip mode predicted by the model and revealed by the texture development, we rationalize that the temperature-induced transition in contraction twinning is due to the increased predominance of basal hai slip at high temperatures (>673 K). Last, our analysis implies that all twin modes studied are rate insensitive and so the strong influence of strain rate and temperature on twinning is due to the rate-sensitivity of slip.

Explicit incorporation of deformation twins into crystal plasticity finite element models

“…2 shows orientation maps based on the electron backscattered diffraction (EBSD) of a deformed microstructure of cast U at a strain of 0.05. In slight contrast to the typical EBSD image of deformed Mg alloys [5], Zr [57], or Ti [39], we observe a large number of relatively thin twin lamellae per grain in cast U. The origin of this unusual twin morphology has yet to be understood.…”

“…It is assumed that all slip and twin systems within the same deformation mode share the same values for critical resolved shear stress (CRSS). This hardening law has been successfully used to model deformation of several metals within mean-field self-consistent codes, differing in crystal structure, such as Haynes 25 [47], AA6022 [48], Nb [49,50], Ta [51,52], Mg [53][54][55], Zr [46,56,57], Be [10,58], and U [4,59,60]. Here, we integrate the same hardening law for U in CPFE and enable the existing CPFE to model the orthorhombic structure.…”

An investigation into the dynamic indentation response of metallic materials

“…For example, the strain rate significantly affects the yielding behavior of metallic materials due to the influences on the dislocation density and pattern, recrystallization, phase transformation, shear bands, etc. [45][46][47][48]. A lower index has been reported for nanoindentation at high strain rate.…”

Effect of local stress fields on twin characteristics in HCP metals

“…For the same twin variant, the lattice reorientation and twin shear for Mg is 86.3 and 13%, respectively. Before additional strain is applied, S TB is close to zero Table 1 The elastic constants [52] and the critical resolved shear stresses (CRSS) values for different plastic modes used in the calculation for Mg [53], Zr [54,55] and Ti [20,56,57]. Only slip modes are considered for the accommodation of plastic deformation.…”