Elastic-plastic Behavior And Phase Transition Characteristic Of Relaxor Ferroelectric PMN-PT Single Crystals By Nanoindentation Experiment

Relaxor ferroelectric PMN-PT single crystals are widely applied in underwater acoustic transducer,piezoelectric actuator,medical ultrasonic transducer and piezoelectric filter due to ultrahigh piezoelectric coefficient.The internal micro-structure of the single crystal is changed under external pressure.The mechanical properties and phase transition characteristics of materials with different orientations have remarkable anisotropy.In this paper,the elastic-plastic deformation of ferroelectric single crystal(100)crystal face and(110)crystal face,and indentation induced micro phase transition are investigated by using the nanoindentation technique.The finite element software ABAQUS is used to study the process of nanoindentation experiment.The crystal orientation of the material in the spontaneous polarization direction is calculated by this finite element tool.The stress distribution and the electric potential distribution under the indentation are analyzed by finite element method.Specific research contents and results are as follows:1.Hardness and young's modulus values with different crystallographic orientations of the single crystal PMN-PT specimens are obtained by the method of Oliver-Pharr.The anisotropy of mechanical characteristics of materials are revealed.The corresponding stress and strain curves are extracted by Hertz theory.2.The load displacement curves of the ferroelectric single crystal materials with different crystal planes were obtained by means of a spherical indenter with the quasi-static displacement loading method.The displacement of indentation depth has a sudden increase resulting in the discontinuity phenomenon(i.e.,pop-in)on the load-displacement curve.The elastic-plastic deformation is revealed by analyzing the pop-in points of the load displacement curves.Quasi static depthcontrol method and dynamic continuous stiffness method are used to obtain the load displacement curves of different crystallographic orientations of specimens with Berkovich indenter.Phase transition characteristics are revealed by analyzing the characteristic points of the local indentation.3.Based on the finite element software ABAQUS,the nanoindentation experimental model of ferroelectric single crystal materials with different crystal orientations was established.The stress distribution,the electric potential distribution and the load displacement curve of the material under nanoindentation are obtained by finite element method.The characteristics of the stress and electric potential of the spontaneous polarization [111] direction crystal under indentation are given.According to the analysis of the stress distribution and the electric potential distribution,it is found that the domain change under the local pressure.