X-ray strain analysis at high pressure: Effect of plastic deformation in MgO

Abstract

Articles you may be interested inHigh pressure equation of state and ideal compressive and tensile strength of MgO single crystal: Ab-initio calculationsThe factors that control the stress-strain state of a polycrystal under differential stress depend on whether or not plastic deformation has occurred in the solid. If not, then the elastic properties with the constraints of the Reuss-Voigt bounds limit this relationship. If plastic deformation becomes important then the Taylor and Sachs models are relevant. These models assume that the plastic process is enabled by dislocation flow on specific lattice planes and specific Burger's vectors. Then, the relationship between stress and strain is controlled by the orientation of an individual grain with respect to the stress field, von Mises criterion, and the critical resolved stress on the dislocation that is necessary for flow. We use a self-consistent model to predict the flow stress during the plastic deformation of polycrystalline MgO with a slip system of ͕110͖͗110͘, ͕111͖͗110͘, and ͕100͖ ϫ͗011͘ at different critical resolved shear stress ratios for the different slip systems. The prediction of the models is correlated with the results of x-ray diffraction measurements. Uniaxial deformation experiments on polycrystalline and single-crystal MgO samples were conducted in situ using white x-ray diffraction with a multielement detector and multianvil high-pressure apparatus at a pressure up to 6 GPa and a temperature of 500°C. A deformation DIA was used to generate pressure and control at a constant deformation rate. Elastic strains and plastic strains were monitored using x-ray diffraction spectra and x-ray imaging techniques, respectively. The correlation of the data and models suggests that the plastic models need to be used to describe the stress-strain observations with the presence of plasticity, while the Reuss and Voigt models are appropriate for the elastic region of deformation, before the onset of plastic deformation. The similarity of elastic strains among different lattice planes suggests that the ͕111͖ slip system is the most significant slip system in MgO at high pressure and high temperature.

Dislocations and Plastic Deformation in MgO Crystals: A Review

“…However, there are limitations, as these equations do not account for plastic deformation. Plastic deformation induces a local relaxation of stress, leading to inconsistent stress interpretations with purely elastic models [255]. Plastic deformation can be modeled, e.g., by comparing the strains measured using XRD to results of elasto-plastic or elasto-visco-plastic self-consistent (EPSC or EVPSC) calculations that account for both elastic and plastic relaxation [253,255,256] (see below).…”

“…Plastic deformation induces a local relaxation of stress, leading to inconsistent stress interpretations with purely elastic models [255]. Plastic deformation can be modeled, e.g., by comparing the strains measured using XRD to results of elasto-plastic or elasto-visco-plastic self-consistent (EPSC or EVPSC) calculations that account for both elastic and plastic relaxation [253,255,256] (see below). Assuming that the experimental textures arise from plastic deformation, they can also be compared with the same polycrystalline plasticity simulations to obtain information about the deformation modes operating in the sample [252].…”

“…The effect of hydrostatic pressure on the polycrystalline rheological law was quantified by experiments up to 10 GPa at temperatures up to 1600 K in the D-DIA [255,263,[273][274][275][276][277]. Most of these studies focused on establishing the stress-strain behavior and rheological laws for MgO.…”

Effect of lattice preferred orientation on lattice strains in polycrystalline materials deformed under high pressure: Application to hcp-Co

“…In such cases, the assumption of a single uniform macroscopic stress applied to all grains and lattice planes within the sample can fail, and stresses deduced for various lattice planes will vary [11,[36][37][38][39][40][41].…”

In situ investigation of MgO nanocube deformation at room temperature

“…At RT, lattice friction competes with solution hardening on the two main slip system families 1/2h1 1 0i{1 1 0} and 1/2h1 1 0i{1 0 0} of the crystalline structure. {1 1 1} and {1 1 2} slips have been observed only in rare and exotic cases [29][30][31]. 1/2h1 1 0i{1 1 0} dislocation glide involves the nucleation of kink-pairs, typical of the lattice friction regime.…”