In Situ Atomic Scale Study Of The Deformation Mechanism Of Metallic Platinum

Metallic nanomaterials have attracted intensive attention due to their excellent physical and chemical properties.In the practical application,nanomaterials are usually under external forces condition that causes them underwent the plastic deformation,thereby shortening the service life of these materials.Therefore,it is very important to study the deformation mechanism of nanomaterials when they are under external force.In this thesis,the deformation tests of the FCC-structure Pt nanowire were performed in a transmission electron microscope(TEM).The plastic deformation mechanism of the nanowires was in-situ studied at the atomic-scale.Our results provided useful information for the establishment of the plasticity theory in FCC structural metal nanomaterial.The experimental results provide guidance for optimization mechanical properties and practical application of metallic materials.The main discoveries are as follow:1.By controlling the magnetron sputtering parameters,a porous Pt film with FCC structure was successfully prepared,which enable us conducted the in situ atomic-scale deformation experiments of Pt nanowires.2.Using the original uniaxial tensile test technique,in situ tensile tests of Pt nanowires with different structures were performed in a transmission electron microscope.The microstructure evolution process of nanowire during the stretching was studied at the atomic scale.The results show that:(1)The plastic deformation of single crystal Pt nanowires is governed by nucleation,movement and annihilation of full dislocations,and partial dislocations are rarely observed.It was found that there are two kinds of plastic deformation model in single crystal Pt nanowires.Model one: The nanowires first processed the homogeneous plastic deformation,then followed by rapid fracture without obviously necking process,this model is different from the previous molecular dynamics simulation.model two: the nanowires first underwent the homogeneous plastic deformation,then followed by an obviously necking process,which is the same as previous molecular dynamics simulation prediction.(2)Through in situ tensile tests of twin structure Pt nanowires,two types of plastic deformation mechanisms were found.The first one is that the partial dislocation slips on the twin boundary,which leads to the twin boundary migration;the other one is the deformation controlled by the twin boundary slip during the plastic deformation.(3)The strain of the nanowire during the deformation was calculated by Peak Pairs Analysis(PPA)software.The tensile stress of the single crystal nanowires is mainly between 1.0 GPa ~ 2.8 GPa.While for the twin structured nanowires,the stress for the twin grain boundaries migration is between 0.8 GPa ~ 2.5 GPa,and the stress for the twin boundary sliding is between 3.11 GPa ~ 5.51 GPa.(4)The deformation process of the tri-crystalline nanowires was in situ observed.The results show that the tri-crystalline nanowires transferred into a single crystal through grain boundary migration during plastic deformation.After the nanowire becomes a single crystal,the plastic deformation was realized by twin nucleation.