Phase Transformation Behavior And Deformation Mechanism Of Zirconia Using Nanoindentation And Molecular Dynamics Simulation

Zirconia ceramic(Ce-TZP)has the characteristics of high strength,hardness and the phase transformation toughening,thus it has became a important engineering materials.And its mechanical behavior and deformation mechanism has became a hot topic for scholars.In this paper,the phase transformation and the relationship between phase transformation and mechanical properties of Ce-TZP during indentation were analyzed by nanoindentation tests.The deformation process of m-ZrO2 at the tip of the indenter was simulated by molecular dynamics method.The atomic configuration and the change of atomic dislocation were studied.(1)Based on the theory of continuous stiffness measurement(CSM),Ce-TZP was subjected to nanoindentation test under five different indentation strain rates and five different indentation depths.According to the Reuss theory we deduce a method for determining the volume fraction of m-ZrO2 in Ce-TZP during nanoindentation,and its reliability was verified by XRD analysis.The results show that due to the effect of phase transformation,Zirconia exhibits strain rate sensitivity during the loading stage.The phase transformation toughening mechanism of Ce-TZP has significant influence on its mechanical properties.The change ofelastic modulus of Ce-TZP is mainly due to the monoclinic phase formed during t?m phase transformation.With the increase of indentation depth,the variation of the elastic modulus and monoclinic volume fraction show the opposite tendency.At a certain depth,the monoclinic volume fraction decreases as the strain rate increases.(2)The molecular dynamics model of monoclinic zirconia was established based on the theory of pair potential proposed by Lewis and the theory of system coulomb potential energy proposed by Wolf,Which was used to simulte the deformation and mechanical behavior of m-ZrO2 at the tip of the indenter during the indentation experiment.The results show that the load fluctuations generated during the indentation is caused by the atomic stacking and dislocation in the crystal.There are different slip surfaces for different press directions and The reason for the load fluctuations is not the same.At different press rates,the P-h curve coincide in the elastic section but it shows the strain-rate sensitivity in the plastic section.At low press rates,due to the effect of stress relaxation there is apparent strain hardening and load fluctuations.