Study And Numberical Simulation On Laser Weling Of TiAl-based Alloy And Nickel-based Superalloy

TiAl-based alloys have been gradually applied to industrial production since the1950s.It has the characteristics of low density,high specific strength and strong creep resistance.TiAl-based alloys have important applications in the production of components such as gas turbines in the defense industry,power plants,and turbine engines in airplanes.The density of TiAl-based alloys is less than half of the one which of Ni-based superalloys.Therefore,the method of using TiAl/Ni-based superalloys to save costs and reduce structural weight has broad application prospects.In this paper,the weldability characteristics of TiAl/Ni-based superalloys are analyzed from the perspectives of metallurgy and stress.In this paper,the joint characteristics of direct welding of TiAl/Ni-based superalloys were first studied.The research results showed that pulsed laser welding cannot effectively connect TiAl-based alloy and Ni-based high-temperature alloy.There was a large crack in the middle of the weld,and after welding the joint cracks immediately.A large amount of Ni,Al,Ti and other elements were detected in the weld.It can be observed that the structure distribution in the weld was not uniform,and the main structures were Al Ni₂Ti and Al_0.35Ni_0.30Ti_0.35 under the light microscope.The hardness test results showed that the hardness of the joints of the TiAl-based alloy and Ni-based superalloy joints was relatively large.The microhardness of the center part exceeded 800HV,which was far greater than the hardness of the base material.In order to change the phase composition of the joint,pure Cu with different thicknesses was used as interlayer to connect the two base materials.When Cu interlayer with the thickness of 0.2mm was added,the two base materials cannot form an effective weld.The main brittle phase formed was basically unchanged.When the thickness of the Cu interlayer was increased to 0.4mm and 0.6mm,the base material can be effectively connected.Both welding zones mainly contain Cr solid solution,（Cu,Ni）solid solution,Al（Cu,Ni）₂Ti/（Cu,Ni）eutectic structure and Al（Ni,Cu）₂Ti.The average tensile strength of the two joints were 158MPa and 88MPa,respectively.The tensile fractures were all on the side close to the TiAl-based alloy.In order to further obtain better joints,composite intermediate layer was used as an interlayer to connect the two base materials.According to the literature,it was found that adding V/Cu composite interlayer can obtain a good joint.Therefor,Ti/V/Cu composite interlayer was added in testing.It was showed that the weld zone was mainly composed by（V,Cr）solid solution phase,Al（Ni,Cu）₂Ti phase and Cu Ni Ti phase.The distribution of hardness in the weld zone was uneven,and the average hardness of the weld zone was 595Hv.The tensile strength of the joint was 169.5MPa,and the fracture occured in the TiAl-based alloy side interface zone.It was speculated that the main reason was that there were a lot of brittle intermetallic compounds such as Al（Ni,Cu）Ti/Al（Cu,Ni）₂Ti in this area.ANSYS finite element software was used for simulation analysis.The temperature field distribution in the welding process was asymmetrical,and the surface temperature of the Ni-based superalloy was relatively high.The addition of copper interlayers of different thicknesses had a significant effect on the maximum temperature of the molten pool.The temperature in the molten pool was higher when the 0.2mm Cu interlayer was used,and the temperature decreases when the 0.4mm and 0.6mm Cu interlayers were used.Excessive thickness of the Cu interlayer was not conducive to improving the welding structure.Due to the decrease of Cu,the temperature of the composite interlayer had increased,which reduced the reflection of the laser and increases the heat input.It was showed from the stress field simulation results that the stress distribution on both sides was asymmetrical and uneven after the cooling for 400s after welding.The stress on the TiAl-based alloy side was higher than that on the Ni-based superalloy side.As the thickness of the Cu interlayer increased,the maximum stress tend to decrease.When the composite interlayer was added,the stress decreases significantly,and the stress was the lowest after the V/Cu composite interlayer was added.It can be shown from the stress distribution curve that the TiAl-based alloy side curve appeared to fluctuate,and the stress distribution was uneven.When single interlayer was added,as the thickness of the Cu interlayer increased,the curve tend to be smooth and the overall stress decreases.When V/Cu composite interlayer curve was added,the stress curve was smooth,which was beneficial to improve the weldability of the joint.