Study On Fine Grain Process By Cold Rolling Heat Treatment And Superplastic Behavior Of GH4169 Superalloy

GH4169 superalloy has excellent high temperature comprehensive properties and is widely used in aerospace,petrochemical,nuclear energy applications and other important fields.However,this alloy has high temperature deformation resistance and serious strain hardening tendency.It is difficult to produce complex heterogeneous parts using conventional methods.The development of superplastic forming technology provides a new way for the processing and forming of this alloy.However,the preparation process of fine-grained GH4169 superalloy is complicated,and problems such as poor microstructure uniformity are prominent.At the same time,the superplastic deformation micromechanism of GH4169 superalloy is still unclear,which severely limits The practical application of the superplasticity of this alloy,in order to solve the above problems,this article focuses on the cold-rolling heat treatment of the GH4169 alloy and the superplastic deformation behavior of the study.The main research contents and results are as follows:(1)The large deformation cold rolling+two-stage annealing process of GH4169 superalloy was developed.The optimal rolling and heat treatment process parameters were determined,the rolling heat treatment process flow was simplified,and fine-grained sheet products with good structure uniformity were obtained.The results were shown that the GH4169 alloy sheet is first subjected to 84%cold rolling deformation,then annealed at 860℃ for 10h,and then annealed at 950℃ for 3h,a fine grain structure with a grain size of 3.56μm can be obtained with good uniformity.(2)The microstructure evolution law and grain refinement mechanism of GH4169 superalloy during cold rolling heat treatment were explored.The precipitation of δ phase and the change rule of matrix structure under different heat treatment parameters were analyzed,and the grain refinement mechanism under cold-rolling heat treatment process conditions was obtained.The results were shown that the large amount of distortion energy stored in the alloy enhances the driving force of static recrystallization during the recrystallization annealing,and the long needle-like δ phase uniformly precipitated in advance promotes the static recrystallization nucleation of the alloy during the recrystallization annealing process.Pinning at the grain boundary hinders the growth of grains,and finally obtains a fine and uniform structure of grains.(3)The superplastic mechanical behavior of fine-grained GH4169 superalloy was studied.The effect of different deformation conditions on the superplasticity of the alloy was studied,the best deformation conditions were obtained,and then the superplastic characteristic parameters of the alloy were obtained.The results were shown that at a temperature of 950℃ and a strain rate of 1.6×10-3s-1,the superplastic elongation of GH4169 superalloy is the highest,which is 756%.When deformed at 950℃,the strain rate sensitivity index of the alloy is 0.53 and the stress index is 1.89.When the strain rate is 4.0×10-4s-1,the deformation activation energy of the alloy is 299.29kJ/mol.(4)The microstructure evolution law and deformation mechanism of GH4169 superalloy superplastic deformation were grasped.Under different deformation conditions,the micro structure evolution of the alloy during the deformation process was studied,and the superplastic deformation mechanism of the GH4169 superalloy was obtained.The results were shown that after superplastic deformation,theδ-phase morphology inside the alloy is mainly block and short rod,the grain size increases,and the grains in the elongation zone all appear nearly equiaxed.Considering both mechanical behavior and micro structure evolution,grain boundary slip regulated by intragranular diffusion is the main mechanism of superplastic deformation of GH4169 superalloy.