Effect Of Machining Parameters On Nano-cutting Of Single Crystal γ-tial Alloy

γ-TiAl alloy has advantages of low density,high modulus of elasticity,high-temperature strength and good flame retardant properties,which has great potential for development in aerospace,turbine blades,automotive industries and other fields.However,γ-TiAl alloy is room temperature brittleness and difficult to deform.In order to improve its processing properties,it is necessary to study its processing mechanism in essence,so it must be analyzed from the atomic scale.Nano-cutting technology is an effective means to reveal the processing mechanism of metal materials through removal of nano-materials.However,whole cutting process and evolution of micro-structure can not be observed from nano-cutting experiments.The molecular dynamics can capture the trajectory,energy and position of a single atom and reveal the evolution of micro-structure in the whole cutting process from all sides.Therefore,in this thesis,single crystal γ-TiAl alloy is taken as the research object,the deformation mechanism,micro-defect evolution and its influence on mechanical properties of materials under different cutting parameters were studied by molecular dynamics simulation method.The specific research work includes following aspects:(1)The nano-cutting model of single crystal γ-TiAl is established by means of molecular dynamics method.Material removal and deformation are described in detail during cutting.The number of subsurface defects and crystal structure transition are accurately studied by using CNA defect recognition technology.The relationship between cutting force and micro-defects is discussed synthetically.In addition,the temperature change and dislocation evolution in the workpiece are explained systematically.(2)The quantitative law of crystal structure transition under different cutting parameters(cutting depth,cutting speed and cutting orientation)are studied.The variation of cutting force,friction coefficient,subsurface defect and machined surface quality under different cutting parameters are analyzed.The results show that the subsurface defects are less and machined surface quality is better when cutting depth is small.The length and depth of subsurface defects are larger,and reaction between dislocations is more when cutting speed is 200m/s.The “V”-shape dislocation loop is generated in workpiece when cutting crystal direction along]011[,and stacking fault tetrahedron is generated in workpiece when cutting crystaldirection along ]001[.In addition,the effects of different cutting parameters on the average temperature of Newton layer and dislocation evolution distribution are explained.(3)Tensile mechanics model is established after different cutting depth is finished.The transformation law of crystal structure before and after cutting are analyzed.The effects of different cutting depth on elastic modulus,stress-strain,the position of dislocation nucleation and fracture morphology of monocrystal γ-TiAl alloy are discussed in tensile stage.The results show that transformation rule of crystal structure before and after cutting is reversed,and the elastic modulus and ultimate stress of workpiece will increase correspondingly at a certain cutting depth.