Study On Microstructure And Properties Of Welded Joint In Vibration Assisted Welding Of Inconel 601H Nickel-Based Alloy

Nickel-based alloys have excellent high-temperature strength and oxidation resistance,therefore these alloys play a significant role in aerospace engine and industrial gas turbine.However,duo to the various alloying elements in nickel-based alloys and the poor thermal conductivity of the alloy,it is easy to produce coarse grains and severe segregation under conventional welding process,which can result in the increased hot cracking susceptibility.In this paper,in order to reduce hot cracking susceptibility and improve mechanical properties of nickel-based alloy welds,applying low-frequency mechanical vibration in conventional welding process to improve the grain refinement and reduce the solute segregation in the weld.Because the crystallization process of weld pool was not visible,in order to obtain the intuitive understanding of the effect of low-frequency mechanical vibration on the crystallization process,firstly,the sodium thiosulfate was utilized to simulate crystallization,to study the nucleation mechanism under mechanical vibration.On this basis,the grain refinement mechanism during the gas tungsten arc welding(GTAW)of Inconel 601 H alloy under various vibration modes and parameters was investigated.And,the effect of grain size,?? phase distribution,element segregation and the width of HAZ on the hot cracking susceptibility was analyzed.Finally,the influence of different vibration modes on the hardness of the welding joint was studied.The results show that: Firstly,when the amplitude was reached 0.2mm,the weld formation was poor.The good weld formation could be obtained when the amplitude was less than 0.2mm.In this condition,it was shown that the basic mechanical properties of the welding joint could be guaranteed.Secondly,significant grain refinement could be achieved in Inconel 601 H alloy welds by low-frequency mechanical vibration.And when the amplitude is 0.2mm,fine and uniform equiaxed grains could be obtained.In terms of the effect of grain refinement of welds,there was a threshold value for the vibration amplitude which was closely related to vibration mode.Different vibration modes led to different effect of grain refinement,which was mainly attributed to the difference of convection induced by the vibration.This condition made the number of free crystals change within weld pool.Thirdly,the fine equiaxed grains and dispersed ?? phase could reduce segregation and enhance grain boundary strength,it was helpful to prevent nickel-based alloys welding solidification cracking initiating.However,the vibration assisted welding significantly increased the width of HAZ of welding joints,which was unfavorable to improve the liquation cracking susceptibility of HAZ.Finally,compared with the conventional welding process,vertical vibration and longitudinal fixation horizontal vibration could significantly improve the hardness of the welding,and the hardness distribution was steady.However,the hardness distribution of the welding fluctuated greatly under transverse fixation horizontal vibration,which was not conducive to improve the comprehensive mechanical properties of the welding.