Molecular Dynamics Simulation Of The Effects Of FCC Phase On Mechanical Behavior And Deformation Mechanism In Nano-titanium

In recent years,with the development of science and technology,the requirements of material properties in the aerospace and marine industries have become more and more strict.Metal titanium has been favored more and more because due to its unique properties.And it has already been demonstrated its unique and powerful vitality.Scientests have confirmed the presense of FCC?face-centered cubic?in titanium and its alloys through experiments and computer simulations.In this paper,molecular dynamics simulation method is used to study the influence of FCC on the mechanical behavior and deformation mechanism of titanium nano-pillars,and provide theoretical basis and reference basis for engineering applications of titanium and titanium alloys.?1?The deformation mechanism of pure?-Ti??-titanium?under loading was studied by molecular dynamics simulation.It was found that disordered atoms were prone to occur in the interior of pure titanium.and stress tended to concentrate at the tip of the system,resulting in dislocation as well as internal stresses release.As the strain increases,the dislocations expand in a ring shape,and the Burgers vector of the dislocation is b=₃¹[112?0],then the dislocations move to the surface of the sample to form a step.With the increases of loading,the perfect dislocation is decomposed into two imperfect dislocations.As the strain increases,the stress and the system energy continues to increase,the extended dislocation begin to bundle on the cylinder,and the full dislocation after the beam set returns to the previous slip surface.which making the completion of a cross-slip.?2?The mechanical properties and microscopic deformation mechanism of nano-titanium with HCP?hexagonal close-packed?and FCC phase is studied under tensile and compress by molecular dynamics simulations.It is found that when the system is subjected to tensile loading,dislocations first occur in the FCC phase,and the movement of dislocation is followed by stacking faults.If the stacking fault has a small atomic density and only one layer of atomic thickness,the dislocations pass through the stacking fault and leave a Lomer-Cottrell lock.If the stacking fault density is high and exceeds two layers of atomic thickness,the dislocation is difficult to pass.Then a large number of stacking faults are generated in the FCC phase.Since the dislocations are separated from each other to form a net-like structure.Under compression loading,the stacking faults formed in the FCC phase accumulate as the HCP new phase,and the reverse transition of the FCC phase to the HCP phase occurs.Which make the new dislocations are difficult to pass through existing stacking faults,forming a new source of defects and transmitting dislocations in new directions.?3?The effect of temperature on the mechanical behavior and deformation mechanism of the two-phase model is studied.The mechanical behavior and deformation mechanism at 70 K,150 K,300 K and 400 K were studied respectively.During compression loading,the temperature was 70 K,150 K,400 K,and the dislocation and stacking faults were generated in the FCC phase.What's more,A<c+a>slip occurred in the HCP phase.In the tensile loading FCC phase,the deformation mechanism at 150K and 400K is consistent with 300K,forming a Lomer-Cottrell lock and a net-like structure.However,twins{1011?}were produced at the interface surfaces of the HCP and FCC phases at 70 K.?4?The effects of FCC phase size on the mechanical behavior and deformation mechanism of the two-phase model were studied.In order to study the influence of FCC phase size on the mechanical behavior and deformation mechanism,a nano-pillar with"sandwich"structure was established.The middle part of the model system was FCC phase of 2 nm,4 nm,6 nm and 8 nm respectively.It was found that in the compression loading,in the FCC phase system,the atomic proportion of the FCC phase of 2 nm and 4 nm sizes gradually decreased until disappeared,the FCC phase was converted into the HCP phase.In the tensile loading,when the FCC phase size is reduced to 2 nm,{1011?}twins are generated on the phase boundary surfaces of HCP and FCC phase.