Nano-indentation Simulation Study On The Effect Of Twin Boundary On γ-TiAl Plastic Deformation And Mechanical Properties

With its excellent high temperature strength,creep resistance,oxidation resistance,high elastic modulus,and low density,TiAl alloy has become the most competitive material in the aerospace,military,and civilian automotive fields.However,the room temperature plasticity of this type of alloy restricts its further development.Considering the superiority of nano-indentation technology to study the plastic deformation process of materials at the micro-scale and the influence of grain boundaries on the plastic deformation of materials in actual engineering,this paper is based on molecular dynamics The effects of indenter positions on different crystal planes on the force-plastic deformation of γ-TiAl alloys during the nanoindentation process were studied,and the effects of twin boundaries at room temperature on the defect evolution and mechanical properties of γ-TiAl alloys were analyzed.The differences of the indentation process under different crystal planes are compared,and the formation mechanism of prismatic dislocation rings in the nanoindentation process is proposed.The research contents are as follows:(1)The nanoindentation process of the indenter on the(110)crystal plane from the grain boundary at 5?,10?,15?,25?,and 40? at room temperature was studied.The load-displacement curve and indentation process at different indenter positions were obtained.The evolution behavior of defects in the steel,calculated the hardness and Young’s modulus,analyzed the dislocation line length,potential energy and temperature change of the test piece at different indenter positions.The analysis found that for the(110)test piece’s nanoindentation process,Its dislocation response is mainly Shockley incomplete dislocations,and the prism dislocation ring in the sample is related to the generation of a large number of stacking faults;during the indentation process,the load curve decreases with the decrease of the hardness curve,resulting in a hardness curve The reasons for the decline include: absorption dislocations at the twin boundary;generation and slip of prism dislocation rings;and a sharp increase in Shockley incomplete dislocations.Factors affecting the increase in hardness are: the mutual reaction between dislocations and dislocation nuclei;twin boundaries hinder dislocation expansion.(2)The nanoindentation process of the indenter at the temperature of(100)on the(100)crystal plane from the grain boundaries at 5?,10?,15?,25?,40? and the indenter position at the center of the(111)plane was studied.This paper compares and analyzes the influence mechanism of twin boundaries on the results of nanoindentation under different crystal planes and the effect of crystal orientation on the evolution of dislocations in γ-TiAl alloy from the perspective of dislocation evolution.The analysis finds that:(100)specimens at different indentation positions of the specimen significantly affects the loading process.When the indenter is closer to the grain boundary,the twin boundary will begin to affect the indentation process in the early stage of indentation.When the grain boundaries are far away,the twin grain boundaries begin to affect the indentation process after reaching a certain indentation depth.The activities of the twin boundaries hindering or absorbing dislocations appear in all nanoindentations under the(100)plane;compared with the nanoindentation processes under(100),(111),and(110)specimens.The surface has the highest modulus of elasticity and hardness,followed by(110),and finally(100).This is because the atomic arrangement of the(111)specimen is the closest and the binding energy is the largest.(3)Analyzed the formation process of prism dislocation rings during the nano-indentation process of(110)and(111)interview pieces,and found that prism dislocation rings were more likely to occur in(110)interview pieces;after the unloading process was completed,The dislocation ring stays inside the grain,and the dislocation ring generated later slips and annihilates under the indenter.The formation mechanism of dislocation rings in γ-TiAl alloy is summarized.Due to the low stacking fault energy of γ-TiAl alloy and the special structure of FCT,dislocations are generated and moved on the prism surface parallel to the close-packed surface(111).Incomplete dislocations surround the internal faults generated by stacking faults.Two parallel internal faults are connected to each other,and finally a prismatic dislocation ring is generated.