Microstructure Regulation And Performance Studies On Ultrasonic Assisted Laser Remanufacturing Of IN939 Superalloy

In the industrial gas turbine,the hot end parts such as the inlet hopper,the turbine disk and the blade are prone to fatigue and damage in a harsh service environment.If they are directly scrapped,it will lead to serious waste of resources and costs.The use of laser remanufacturing technology to repair damaged hot end parts will greatly reduce costs and resource waste,and has great social and economic value.Laser remanufacturing technology is a laser repairing technology that combines remanufacturing engineering and laser cladding technology to remanufacture damaged parts and prolong the service life of damaged parts.However,the superalloy used in the hot end member is prone to defects such as pores,harmful phase precipitation,and poor fusion in the laser repairing process.To overcome these problems,ultrasonic vibration was introduced into the laser remanufacturing process of superalloy.And the forming quality,microstructure and comprehensive performance of laser remanufactured region of IN939 superalloy were studied.This study provides the theoretical basis and technical support for the remanufacturing of the hot end parts of industrial gas turbines.Based on the influencing mechanism of ultrasonic vibration in the process of metal solidification,this study firstly designs the ultrasonic horn,completes the ultrasonic assisted laser remanufacturing equipment,and realizes the effective coupling of ultrasonic vibration and laser beam.Combining the macroscopic forming quality and the microstructure,the process studies and parameter optimization were carried out for laser cladding of IN939 superalloy.Furthermore,ultrasonic vibration was introduced into the laser cladding process to study the effects of ultrasound on the morphology,microscopic defects,microstructure,crystal orientation,element segregation and distribution of cladding.Through the establishment of the simulation model,the effects of ultrasound on the temperature field and flow field of the internal molten pool of the V-shaped groove are explored.Furthermore,the effects of ultrasonic vibration on the microstructure,element segregation and crystal orientation of the laser-reformed Vgroove are analyzed.Finally,the analysis of the room-temperature hardness,elevatedtemperature hardness,corrosion resistance and tensile properties of ultrasonic assisted laser remanufactured parts was carried out.The main conclusions of this study are as follows.(1)Ultrasonic vibration significantly affects the macroscopic morphology of the IN939 superalloy cladding layer.The main influences are the increase of the penetration depth and the melting width,as well as the decrease of the melting height.(2)Ultrasonic vibration significantly affects the microstructure of IN939 superalloy repaired zone.The primary dendrite spacing near the interface bonding zone is reduced from 6.74 ~ 11.59 ?m without ultrasonic application to 2.85 ~ 6.09 ?m.Ultrasonic vibration effectively suppresses Laves phase and the segregation of MC phase.The content of precipitated phase is significantly reduced,and the distribution is more dispersed.Ultrasound promotes the uniform distribution of Fe,Co and other elements in the cladding layer,avoiding the formation of rich Fe-rich Co region.Ultrasonic vibration effectively reduces the porosity of the cladding layer.The EBSD test results show that the ultrasonic vibration significantly reduces the grain size and reduces the crystal orientation uniformity.(3)Introducing ultrasonic vibration into the laser repairing process of IN939 superalloy V-groove is able to effectively avoid defects such as tip porosity,inhibit element segregation in repaired zone,and reduce primary dendrite spacing and grain size.Based on numerical simulations,the mechanism is as follows.The convection of the molten pool is accelerated under the action of ultrasound.Both the flow rate and the cooling rate is increased,and the maximum temperature in the molten pool is lowered.The temperature field distribution becomes more uniform.(4)Based on the microstructure control by the ultrasonic vibration,the performance of the IN939 superalloy repaired zone was significantly improved.The hardness of the repaired zone increases by 7.41% at room temperature,and the elevated-temperature hardness increases by 10.42%.The corrosion resistance is improved.The tensile test showes that the tensile strength and the yield strength of the laser repaired parts increases by 5.95% and 9.26% affected by the ultrasonic vibration,respectively.