Modeling analysis of the influence of plasticity on high pressure deformation of hcp-Co

Abstract

Previously measured in situ x-ray diffraction is used to assess the development of internal elastic strains within grains of a sample of polycrystalline cobalt plastically deformed up to a pressure of 42.6 GPa. An elastoplastic self-consistent polycrystal model is used to simulate the macroscopic flow curves and internal strain development within the sample. Input parameters are single-crystal elastic moduli and their pressure dependence, critical resolved shear stresses, and hardening behavior of the slip and twinning mechanisms which are active in Co crystals. At 42 GPa, the differential stress in hcp-Co is 1.9Ϯ 0.1 GPa. The comparison between experimental and predicted data leads us to conclude that: ͑a͒ plastic relaxation plays a primary role in controlling the evolution and ordering of the lattice strains; ͑b͒ the plastic behavior of hcp-Co deforming under high pressure is controlled by basal and prismatic slip of ͗a͘ dislocations, and either pyramidal slip of ͗c + a͘ dislocations, or compressive twinning, or both. Basal slip is by far the easiest and most active deformation mechanism. Elastoplastic self-consistent models are shown to overcome the limitations of models based on continuum elasticity theory for the interpretation of x-ray diffraction data measured on stressed samples. They should be used for the interpretation of these experiments.

Dislocations and Plastic Deformation in MgO Crystals: A Review

“…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].…”

Strength and elasticity of niobium under high pressure

“…Attempts have been made more recently to include the effect of plastic deformation through numerical modeling. 36,37 Karato stated that some important physics is missing in the model of Singh 12 and proposed a general theory. 38 The Karato model postulates that each crystallite in a polycrystalline aggregate under nonhydrostatic compression experiences a stress that deforms the grain.…”

Texturing in Earth’s inner core due to preferential growth in its equatorial belt

“…Experimental determination of the elastic constants suggest a fast direction lying at an intermediate angle between the a and c-axes (Mao et al, 1998;Merkel et al, 2005), but the technique that was used includes serious artifacts related to stress heterogeneities induced by plastic deformation (Antonangeli et al, 2006;Merkel et al, 2009). At inner core pressures and temperatures, Steinle-Neumann et al (2001) found a reversal of anisotropy, with the a-axis faster than the c-axis but the validity of their calculation has been questioned (Gannarelli et al, 2003(Gannarelli et al, , 2005).…”