Computational And Experimental Investigation Of Microstructural Evolution During Hot Deformation Of IN 690 Alloy

IN690 alloy is a nickel-based high-temperature alloy,because of its low carbon content and high nitrogen content,it is considered to be an ideal alternative material for IN600 alloy.IN690 alloy has the characteristics of excellent mechanical properties,good formability,and good corrosion resistance Hot extrusion is a key step in the manufacturing process of IN690 alloy pipes,which may cause cracks in the pipe due to work hardening?WH?during processing.Therefore,hot working is widely used as a method to optimize the structure of superalloys and improve their mechanical properties.The hot working process is very sensitive to process parameters such as temperature,strain rate and true strain.There are some complex metallurgical phenomena?including:WH,dynamic recovery?DRV?and dynamic recrystallization?DRX?,etc.?that need to be solved during the hot working process.Therefore,it is of great significance to study the DRX behavior of IN690 alloy.A Gleeble-3500 thermal simulation test machine was used to perform thermal compression tests under different deformation conditions?temperature 950-1100°C,strain rate 0.01-1 s-1,maximum true strain 0.8?.The flow stress curve of IN690 alloy is analyzed,and the high temperature constitutive model and DRX dynamic model of IN690 alloy are created,revealing the change law of flow stress curve.Through metallographic microscope?OM?,electron backscatter diffraction?EBSD?and transmission electron microscope?TEM?and other characterization methods,systematically studied the effect of thermal deformation parameters on the evolution of IN690 alloy structure and discovered the DRX mechanism of IN690 alloy.In addition,this paper also uses the finite element simulation?FEM?software to simulate the evolution process of microstructure.In summary,the conclusions of the test are as follows:The flow stress of IN690 alloy decreases with increasing temperature and decreasing strain rate.The flow stress curve of IN690 alloy is divided into three different stages,namely WH stage,DRV stage and DRX stage.The IN690 nucleation mechanism is mainly based on discontinuous dynamic recrystallization?DDRX?,supplemented by continuous dynamic recrystallization?CDRX?.DDRX usually occurs at the deformed grain boundary,and the crystal nucleus grows in the high energy region.The main feature of the DDRX mechanism of IN690 alloy is the grain boundary bowing.CDRX usually occurs inside the original grains.The main feature of the CDRX mechanism of IN690 alloy is that the rotation of subcrystals is accompanied by the migration of low-angle grain boundaries?LAGBs?to high-angle grain boundaries?HAGBs?.The evolution process of substructure is as follows:first,high-density dislocations are concentrated near the original grain boundary,and secondly,high-density dislocations are transformed into sub-grains,and finally DRX grains are formed.Dislocation rearrangement and annihilation occur during the DRX process and are accompanied by the migration of LAGBs to HAGBs.The DRX process of IN690 alloy was simulated by using FEM software.The test results verify the correctness of the calculation model and predict the DRX process.The results show that the increase in deformation temperature and the decrease in strain rate will increase the dynamic recrystallization volume fraction of IN690 alloy(X_DRX)...