Study On Temperature Field And Stress Field Of Ti₂AlNb Electron Beam Welding

The ? stable element Nb in Ti₂AlNb alloy can increase the melting point of the material and improve the room temperature plastic toughness of?₂ phase.it can reduce weight by more than 40%when it is used in aero-engine instead of nickel-based alloy.Brittle-hard intermetallic compounds are easily formed in Ti₂AlNb alloy joints during welding,which are accompanied by reheat cracks and microstructure discontinuities.Based on the advantages of concentrated energy density,large aspect ratio and small deformation of electron beam welding,the main research work of this paper combined with Ansys finite element software is as follows:(1)the temperature field change of Ti-22Al-25Nb alloy during electron beam welding is simulated by compound heat source model,the thermal cycle curve distribution under different process parameters is obtained,the phase transformation of HAZ is predicted,and the factors affecting weld pool morphology are analyzed.(2)the thermal indirect coupling method is used to simulate the residual stress distribution in each path of the weldment,and to explore the relationship between the process parameters and the variation of three-dimensional residual stress in the weld.The analysis of temperature field shows that the energy density of"Gaussian plane+Gaussian rotation"is higher than that of"Gaussian plane+improved cone"compound heat source with the same parameters,and the cross section of the molten pool can better reflect the deep penetration keyhole morphology of electron beam welding.During welding,the long and narrow elliptical isotherms are symmetrically distributed on both sides of the weld around the heat source,and the stress is basically unchanged after cooling to room temperature.The orthogonal test shows that the electron beam has the greatest influence on the weld size,followed by the welding speed.The temperature of the weld is 2000 to 3000?,and the heat-affected zone(HAZ)2mm away from the weld is 800 to 1300?.The cooling rate of the weld center is 835?/s,which is much higher than the critical cooling rate of B2 phase,which is the main reason for the formation of single B2 phase in the weld.The stress field analysis shows that the equivalent stress is concentrated in the weld and HAZ.The distribution of residual stress in the 3mm from the weld is very complex,and the different timing of solidification and cooling is the main cause of stress concentration.The three-dimensional stress analysis of each section shows that the transverse stress along the weld and HAZ is concentrated at both ends and the transition in the middle is smooth;the longitudinal stress is about the high tensile stress of 600MPa;the peak value of normal stress and transverse stress are smaller,about 100MPa.The three-dimensional stress of the vertical weld forms a narrow tensile and compressive stress range near the seam,and then tends to be stable.The simulation test shows that the residual stress can be reduced and moved to the side of the base metal by reducing the welding speed and increasing the electron beam current.The optimum process parameters are as follows:electron beam current 10m A,welding speed 360mm/min,acceleration voltage 60kV.