Deformation Mechanism Of Dual-phase TiAl Alloy Under Nanoindentation

The Ti Al alloy with dual-phase layer structure composed of?-Ti Al and?₂-Ti₃Al is a lightweight alloy with high elastic modulus,high specific strength and excellent high-temperature performance.It has been widely paid attention as a competitive new material in aviation,aerospace and automotive fields.At present,the research on Ti Al alloys is mainly focused on?-Ti Al,while there are few studies on dual-phase Ti Al alloys.Therefore,based on the molecular dynamics simulation method,this paper studies the nanoindentation of the dual-phase Ti Al alloy by the thickness of the lamella and the phase boundary.The effect of defect evolution and mechanical properties in the process,the deformation mechanism of the material is discussed from the atomic scale,and the dislocation nucleation and evolution process in different phases are analyzed,so as to deepen the understanding of the plastic deformation process of the dual-phase Ti Al alloy.The main research contents and results are as follows:(1)The effect of lamella thickness on the mechanical properties of dual-phase Ti Al alloys is studied.The nanoindentation process when the indenter acts on the?and?₂ phases of the samples with different layer thicknesses is simulated,and the load-depth curves and defects of the indenter acting on the?and?₂ phases under different layer thicknesses are obtained.During the evolution process,the hardness and elastic modulus were calculated,and the temperature and potential energy changes of samples with different thicknesses during the indentation process were analyzed.The research results show that the hardness of the material increases with the decrease of the thickness of the lamella,which is in line with the Hall-Petch relationship.When the thickness of the lamella is reduced to 70?,the hardness of the material reaches the maximum value.With further reduce of the lamella thickness,on the contrary,the hardness decreases,showing an inverse Hall-Petch relationship;the elastic modulus of the material will also change with the change of the thickness of the lamella.The critical load during the elastoplastic transformation of the material will decrease as the thickness of the lamella decreases.In the nanoindentation process,when the indenter is pressed into the?phase,the deformation behavior is dominated by stacking faults on the{111}plane.When the head is pressed into the?₂ phase,the deformation behavior is dominated by the stacking faults on the(0001)basal surface.The movement of the dislocations on the basal surface will cause phase transitions on the material surface,and the prismatic surface slip is activated.The temperature and potential energy of the system vary with The depth of the indentation increases,and the smaller the thickness of the lamella,the faster the change.(2)To study the effect of different positions of the indenter from the phase boundary on the mechanical properties of the dual-phase Ti Al alloy when the indenter is parallelled to the?/?₂ phase boundary.The nanoindentation process when the indenter at different distances from the phase boundary is simulated,and the defect evolution and the mechanism of action at different distances between the?and?₂phases are analyzed.The hardness and elastic modulus of the material are calculated through the load-depth curve.The change trend of potential energy and temperature is studied,and the influence of different phase boundary orientations on the deformation mechanism and mechanical properties of the material is analyzed.The research results show that the distance between the indenter and the phase boundary does not affect the critical load when the material undergoes initial plastic deformation.The critical load of the?₂ phase is bigger than that of the?phase,and the?phase is more prone to plastic deformation.The closer indenter is to the phase boundary,the greater the hardness of the material,the greater the elastic modulus.During the indentation of the?₂ phase,nanocrystalline grains are produced and can hinder the movement of dislocations.The sample with closer distance between phase boundary and indenter,in the process of nanoindentation,the better the mechanical properties of the material.The higher the temperature generated,the faster the potential energy changes.