Molecular Dynamics Study On Deformation Behavior Of Single Crystal Titanium Nanowires With Initial Defects

Titanium is one of the most important metal materials in this century.Because of its unique properties such as high hardness,high melting point and low density,it has a very wide application prospect.With the development of modern technology,The mechanical properties of micro nano metal instruments made of titanium should be further improved.Single crystal nanowires are the basic components of micro nano electromechanical systems.It is increasingly important to study the deformation mechanical behavior of titanium nanowires.As we all know,the existence of micro defects in metals is inevitable.Therefore,molecular dynamics simulation technology is used to simulate the tensile and shear loading of single crystal titanium nanowires with initial defects in this paper.The aim is to investigate the effect of initial imperfections on the mechanical behavior and deformation mechanism of SCTNW.In addition,the effects of ambient temperature,loading orientation and loading strain rate were also studied.The stress-strain curves of SCTNW under different loading conditions were obtained.The mechanical behavior and deformation mechanism are analyzed.The conclusions are as follows:(1)The yield strength of SCTNW decreases with the increase of the ratio of initial defects,but has little effect on the elastic modulus.At room temperature,the stress-strain curve and deformation mechanism of SCTNW with 1%-2% point defects are similar to those without defects,they experienced two stages of elastic-plastic deformation.The primary plastic deformation is dominated by twinning,while the secondary plastic deformation is dominated by hcp-fcc phase transformation.The deformation mechanism of sctnw changed greatly when the point defects accounted for 3%-5%.Firstly,the number of twins with initial nucleation increases,and secondly,dislocation slip dominates the secondary plastic deformation.The effect of initial point defects at low temperature is not significantly different from that at room temperature.At high temperature,the low proportion point defects make the plastic deformation not only twin but also slip obviously,and for the point defects with high concentration,the second twinning deformation is very obvious.(2)The yield strength and elastic modulus of SCTNW decrease obviously with the addition of initial volume defects.The results show that when the sctnw is stretched along the[11-20]direction,a similar strengthening stage occurs after the first yield,the plastic deformation is dominated by dislocation slip,and there are very obvious and smooth slip steps,which are still the same after the addition of volume defects.When stretching along the direction of[-1100],compared with the former two directions,the yield strength of sctnw decreases more obviously with the addition of volume defects.The plastic deformation of nanowires is mainly caused by dislocations with 1/3<1-210>Burgers vector and 1/3<-1100>Shockley partial dislocation slip.(3)The effect of initial edge dislocation on the shear loading of nanowires is slight,and the reaction is the decrease of strength.However,there is an anomaly when the [-1100] crystal is loaded downward.For the [-1100] orientation,the dislocation decomposition reaction occurs at the initial stage,and it immediately slid off the surface of the nanowire.For [0001] orientation,the initial edge dislocations are decomposed into partial dislocations.However,due to the fact that some dislocations can not move and slip on the base plane,they are decomposed into partial dislocations step by step.After that,reverse twinning appeared in the nucleated twins.