Effect Of Temperature On Tensile Deformation And Fracture Behavior Of GH4169 Fiber Laser Welded Joint

With the rapid development of modern aviation industry,the aero engine is becoming more and more demanding for the safety of service.The service environment of the hot end components for aero engines is worse with ever-increasing thrust weight ratio of aero engines.It is proposed more stringent requirements for the service reliability of the material and connection structure for the key components.And the various components of aircraft engine,such as rocket launchers of combustion chamber and adjustment sheets of tail vent are welded structures.The unconventional deformation and fracture of the welded components is often caused when these components suffer the effects of high temperature,thermal stress,disassociation vibration stress and damaged and peeled blade impact,which leads to significant economic losses and security risks.The present study aims to study the microstructure,microhardness distribution and microstructure evolution behavior of laser welded GH4169 superalloy joint to examine the effects of deformation temperature on the tensile properties and deformation behavior of the welded joint fabricated under the optimum process parameters.The deformation behavior and fracture mechanism of the welded joint at high temperature and high strain rate is also explored.The results show that the fiber laser welded joint of GH4169 alloy is composed of the base metal,heat-affected zones,columnar crystal zone and equiaxed crystal zone from the base metal to the weld centerline,compared with that of the pulsed YAG laser welded joint.There is no softening phenomenon in the fiber laser welded joint without heat treatment.The microhardness difference between the fusion zone,heat-affected zone and the base metal is close to zero of the welded joint after heat treatment.Both of the yield strength and tensile strength of the laser welded joint are higher than those of the base metal of GH4169 alloy.The strength of the welded joint decreases with the increase of temperature,while the plasticity shows an overall increasing trend.At low temperature(<600?),the strength of the welded joints decrease with the increase of temperature,but the change is not obvious,and the plasticity increases slowly.When the temperature exceeds 600?,the strength decreases significantly,and there is a significant increase in plasticity.As the temperature increases,the tensile fracture position of the welded joint transfers from the fusion zone to the base metal.It is the essential reason for the changing tensile fracture position with increasing temperature that there is a significant difference in the plastic deformation ability and deformation mode of different subzones in the welded joint of GH4169 alloy under different deformation temperatures.At room and high temperatures,the strength of base metal and welded joint of GH4169 alloy increase significantly with the increase of strain rate.With increasing strain rate,the plasticity of base metal decreases,while the plasticity of welded joint increases slowly.At the same strain rate,the strength of welded joint of GH4169 alloy is higher than that of base metal,and plasticity is less than that of base metal.With the increase of strain rate,the tensile fracture position of welded joint of GH4169 alloy gradually moves from the fusion zone towards the weld centerline.The difference of plastic deformation capacity and the distribution of plastic strain of the various microstructures in different weld subzones determine the overall plastic deformation behavior and the failure mode of welded joint during high temperature deformation.