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An Atomistic-Informed Phase-Field Model for Non-Isothermal Phase Transformation and Plasticity in Yttria-Stabilized Tetragonal Zirconia

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Document pages: 24 pages

Abstract: We propose an elastoplastic phase-field (PF) model to investigate the mechanics of tetragonal-to-monoclinic phase transformation (TMPT) and elastoplastic deformation of yttria-stabilized tetragonal zirconia (YSTZ). A Landau polynomial with non-vanishing chemical energy at the equilibrium temperature is introduced to account for the actual formation energies of the phases. The effects of different grain orientations, grain boundaries, latent heat, and temperature on TMPT and deformation mechanisms are considered. The simulation results for single crystals demonstrate the capability of the model to reproduce the orientation-dependent compressive deformation of YSTZ similar to atomistic simulations and micropillar experiments. The single crystal with [100] crystallographic orientation along the loading direction (SC[100]) displays both TMPT and plasticity, SC[101] experiences only phase transformation, while SC[001] undergoes only plastic yielding. The TMPT induced by compressive loading exhibits shape memory effect (SME) below the equilibrium transformation temperature and pseudoelasticity above it, while the critical transformationstress increases when the loading temperature increases. The irrecoverable plastic strain is found to trap part of the monoclinic phase, which prevents a complete reverse transformation. The polycrystalline cases also display SME and PE, respectively, at low and high temperatures. Due to the orientation differences between grains and the stress concentrations at geometric nonlinearities, plastic deformation occurs in polycrystalline YSTZ for an applied load less than the yield stress. The results suggest a possible limitation of plasticity and an improvement of the shape recovery of YSTZ if one can control the orientation of the grains and or increase the density of stacking faults at the grain boundaries during material processing.

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