Study On Microstructure Of Nickel-based Alloys Welded Joint Based On Combination Of Vibration And Rapid Cooling

Nickel-based alloys have good hot corrosion resistance,oxidation resistance,and microstructure stability at high temperatures.Therefore,they play an important role in the fields of aerospace engine and power turbine.However,due to the variety of nickel-based alloy elements,poor fluidity and low thermal conductivity of alloy solutions,it easy to produce microscopic segregation and coarse grains of welded joints under the conventional gas tungsten arc welding(GTAW),which increase the hot cracking susceptibility.Previous studies have shown that only the mechanical vibration acting in the welding process can refine the grains at the weld center,but there were still many fine columnar grains in the upper part of the weld edge.The heat-affected zone(HAZ)morphology was eventually dominated by coarse grains,and the width of the HAZ increased.However,the grains of the welded joint are refined in the rapid cooling process.Therefore,in this paper,the combination of vibration and rapid cooling is applied to the welding process to further improve the grain size and microscopic segregation of the welded joint,so as to achieve the purpose of controlling the welding hot cracking more effectively.Firstly,the effect of the combination of vertical vibration and rapid cooling on Inconel601 H alloy welded joint is studied.The results show that under the compound physical fields,the weld was basically fine equiaxed grains,the problem of more columnar grains in the upper of the weld edge was improved,and the width of the HAZ and grain size were reduced compared with conventional GTAW and vibration GTAW.In the weld,the ??phase was reduced and exihibited a more fine and uniform discrete distribution.The segregation of Ti elements decreased obviously,the hardness of the weld was further improved and the distribution was more uniform.Secondly,the mechanism of grains refinement was analyzed by combining with the physical simulation.In the compound physical fields,the degree of supercooling of liquid metal in the welding pool increased obviously,which promoted the formation of more crystal nuclei.The crystal nucleus at the edge of the welding pool was less effect by the high temperature liquid in the center of the pool.Therefore,the more crystal nuclei can be remained.Moreover,the maximum temperature in the HAZ was also significantly reduced.Therefore,the grains of welded joint were significantly refined.Finally,the influence of compound physical fields on microstructure of Inconel 625 alloy welded joint was studied.The results showed that there was no obvious dividing line between the base metal and the HAZ under conventional GTAW.In the vertical vibration condition,the welding are basically shorter dendrites,while the vibration also leads to the width of the HAZ increased and the coarse grains.In the rapid cooling process,equiaxed grains appeared in the weld,the dendrite spacing was significantly reduced,and the grains in the HAZ were significantly refined.The compound physical fields not only refined the grain of the weld,and the weld was basically fine dendrite,but also made the grain in the HAZ more refined than the conventional GTAW and vertical vibration GTAW.The eutectic structure of the Laves brittle phase in the weld changed from continuous network to fine dispersion precipitation,and the amount significantly decreased.The hardness value of the weld was increased and evenly distributed.