Computer Simulation Of Mechanical Tensile Properties On Grain Boundary In Bicrystal γ-TiAl

Grain boundary,acted as an important surface defects,plays a vital role on material mechanics properties.On the grain boundary,the arrangement of atoms transforms from one orientation to another orientation,so the atomic arrangement is irregular and grain boundary is in the transition state,which makes the grain boundary with some special properties differ from grains on both sides.Using molecular dynamics and crystal plasticity finite element,this paper simulates bicrystal γ-Ti Al with different orientation of grain boundary and analyses the dislocation nucleation,the slip system and mechanical properties under different strain rate and temperature during the unaxial tension.This study selected four bicrystal γ-Ti Al including Σ3(111)109.5° grain boundary,Σ3(211)70.5° grain boundary,Σ5(210)36.9° grain boundary and Σ9(310)38.9° grain boundary.We analysed the variation of the stress and strain and the startup of slip system by uniaxial tensile test of crystal plasticity finite element simulation.We analysed the effect of grain boundary on the dislocation nucleation mechanism by uniaxial tensile test of molecular dynamics simulation under different strain rate of 1×108s-1,1×109s-1 and 1×1010s-1 and the different temperature of 1K,100 K,300K and 600 K.The results of crystal plasticity finite element demonstrated that except for the bicrystal one containing Σ3(111)109.5° grain boundary,bicrystal two containing Σ3(211)70.5° grain boundary,bicrystal three containing Σ5(210)36.9° grain boundary and bicrystal four containing Σ9(221)38.9° grain boundary showed varying degrees of stress concentration phenomenon at the grain boundary.According to stress on the grain boundary,they changed with the sequence as follow: bicrystal one containing Σ3(111)109.5° grain boundary > bicrystal two containing Σ3(211)70.5° grain boundary > bicrystal four containing Σ9(221)38.9° grain boundary > bicrystal three containing Σ5(210)36.9°.The level of stress value is directly proportional to the misorientation of grain boundary.We simulated bicrystal γ-Ti Al containing four different grain boundarys during the unaxial tension under the strain rate of 1×108s-1,1×109s-1 and 1×1010s-1.The results showed that the peak stress of bicrystal γ-Ti Al is proportional to the strain rate.We simulated bicrystal γ-Ti Al containing four different grain boundarys during the unaxial tension under the temperature of 1K,100 K,300K and 600 K.The results showed that the elastic modulus,yield stress and peak stress of bicrystal γ-Ti Al are inversely proportional to the temperature.The orientation of grain boundary is an important factor which affects the mechanical properties of bicrystal γ-Ti Al,and it is also related to the number of slip systems and the slip of dislocation during the process of deformation.Among four kinds of grain boundarys,the strength of Σ5(210)36.9° grain boundary is reduced.The Σ3(211)70.5° and Σ9(310)38.9° grain boundary show obvious stress concentration phenomenon,which is easy to produce fatigue crack during the process of deformation.Not only can Σ3(111)109.5° grain boundary improve the strength of the material,but also increase the capacity of plastic deformation.