Study On Acoustic Emission Response On Fracture Behavior Of TiAl Alloy Based On Molecular Dynamics

TiAl alloy has excellent properties such as low density,high strength and high temperature oxidation resistance.It has a good application prospect in the fields of aero engine,automobile and ship.During the preparation and processing of TiAl alloy,dislocations,holes,cracks and other defects are inevitable.Under external conditions,the evolution of defects will release strain energy,and part of the strain energy is released in the form of elastic wave,resulting in acoustic emission.Due to the different characteristics of acoustic emission signals produced by different defects,the type of acoustic emission source can be determined and its evolution behavior can be analyzed by extracting acoustic emission signals and processing acoustic emission signals.Therefore,based on the molecular dynamics method,this paper reveals the defect evolution behavior and acoustic emission response mechanism in the process of material deformation and fracture at the nanoscale.The main results are as follows:(1)Uniaxial tensile simulation of bicrystal TiAl alloy with voids was carried out.It is found that the size and location of the hole have little effect on the elastic modulus of the material;after plastic deformation,the twin boundary has a blocking effect on the continuous emission of dislocations at the edge of the hole,which increases the crystal strength;compared with the samples with intragranular holes,the samples with grain boundary holes are more likely to produce stable dislocation structure when reaching the yield stress,which hinders the movement of dislocations and improves the crystal strength;in addition,the yield strength of the material decreases with the increase of the hole size.(2)Uniaxial tensile simulation of TiAl alloy samples with different twin spacing was carried out.It is found that the Shockley incomplete dislocation loops are formed at the edge of the hole under tensile load,and the initial plastic deformation begins with the Shockley incomplete dislocation movement.The yield stress decreases linearly with the increase of the twin boundary spacing.The smaller the twin boundary spacing is,the more twin boundaries are,and the more dislocations slip and penetrate The more twin boundary is,the greater resistance will be.In the specimen with smaller twin boundary spacing,the blocked dislocations are easy to accumulate due to less slip space,which leads to material strengthening.The increase of twin boundary spacing makes the number of dislocations increase during plastic deformation,which leads to the increase of acoustic emission signal quantity and strength.(3)In the tensile process of TiAl alloy with voids and twin boundaries,the acoustic emission sources mainly include lattice vibration,dislocation activity and crack propagation.Stress and kinetic energy analysis,acoustic emission power and median frequency distribution and energy integration analysis all show that acoustic emission signal mainly comes from lattice vibration,and has a large power range and low median frequency,The acoustic emission signals of dislocation slip show the characteristics of wide frequency domain,the acoustic emission signals of dislocation proliferation and dislocation stacking show the characteristics of low power,and the acoustic emission signals of crack propagation belong to sudden type,showing the characteristics of high frequency and high power.