Effect Of Temperature And Niobium On Mechanical Properties Of Polycrystalline Gamma-TiAl Alloy

With the development of aerospace and automobile industry,the influence of temperature on material properties is becoming more and more important.More and more scholars begin to pay attention to the influence of temperature on the properties of materials.With the increase of temperature,the microstructure of metals will change,which will lead to the change of mechanical properties.For polycrystalline metal materials,temperature has a great influence on grain boundary and grain size,and temperature affects the microfracture mode of the material,and when the temperature is too low,the mechanical properties of the metal material will be significantly reduced,and the material will be cold and brittle when the temperature is too low.gamma-TiAl alloys are widely used in aerospace,aerospace and automotive industries.Their room temperature brittleness and high temperature plasticity restrict their development.However,these defects can be improved by alloying Ti-Al-Nb.In order to further understand the effect of temperature on the properties of polycrystalline gamma-TiAl alloy,a polycrystalline gamma-TiAl alloy model was constructed by using Voronoi algorithm.The tensile deformation of polycrystalline gamma-TiAl alloy without niobium and niobium was simulated by molecular dynamics.The effects of temperature on the mechanical properties and microcosmic mechanism are studied.The following conclusions are obtained:(1)The effect of temperature on the mechanical properties and microstructure evolution of niobium-free polycrystalline gamma-TiAl alloy.With the increase of temperature,the number of dislocations produced in the initial model grain after relaxation will increase sharply,the critical strain value of crack initiation in the system increases,the yield strength of polycrystalline gamma-TiAl alloy decreases gradually,the elastic modulus shows a nonlinear decreasing trend,the ductility of the material increases,the plastic deformation occurs more easily,and the total energy increases,which makes the system more unstable.When the temperature rises to 1000 K,the material was occured brittle-ductile transition.In the tensile process,the material firstly nucleates the dislocation at the triple grain boundary,emits it into plastic deformation,and the grain boundary hinders the slip of the dislocation,and with the increase of temperature,obvious grain rotation and grain boundary slip occurred in the material.Under the same stress,the number of emitted dislocations will increase,and the grain boundaries will emit dislocationscontinuously during the loading process.When the applied load increases,the dislocations emitted increase and the effect on plastic deformation increases.(2)The effect of temperature on the mechanical properties and microstructure evolution of niobium-containing polycrystalline gamma-TiAl alloy.With the increase of temperature,the number of dislocations produced in the initial model grains increases after relaxation,the yield strength of the alloy decreases,the elastic modulus shows a nonlinear decreasing trend,the ductility of the alloy increases,the plastic deformation occurs more easily,the total energy increases,and the system becomes unstable.Due to the addition of niobium element,the room temperature plasticity and fracture toughness of titanium aluminum alloy are improved,but its brittleness is enhanced and the crack initiation position changes.In the loading process,the material firstly emits dislocations at the grain boundary of the triple and undergoes plastic deformation,the grain boundary hinders the slip of dislocation.With the increase of temperature,the grain rotation and grain boundary slip become more obvious,and the critical stress of dislocation emission decreases.Under the same stress,the amount of dislocation emitted by grain boundary increases.Under1200 K,the segregation effect of niobium element occurs,with the increase of temperature,more niobium atoms are segregated at grain boundaries,the thickness of grain boundaries increases.the dislocations emitted by grain boundaries increase with the increase of tensile strain.And then the effect on plastic deformation is also increased.