Research On Macro-Micro Deformation Behavior Of GH710 Superalloy And Hot Rotary Forging Of Turbine Disc

In recent years,with the continuous improvement of the performance of advanced aerospace engines,a large number of key components such as turbine discs have been formed with difficult-to-deform materials such as GH710 for integral structural forming,which means the standard requirements are high,the process is complex,and the producing is difficult.In addition,the GH710 used for the turbine disc has a large degree of alloying,complex microstructure changes,large deformation resistance during high-temperature deformation,and a narrow range of process parameters.The range of process parameters is the premise of forming high-performance GH710 turbine discs.Therefore,this paper takes GH710 as the research object and uses thermal simulation experiments,SEM and EBSD analysis methods to study the high-temperature deformation behavior and microstructure evolution of GH710,build the hot processing map and determine the thermal processing window for GH710.According to the hot deformation characteristics of the alloy,a piecewise constitutive relation model and a dynamic recrystallization model are established.Aiming at the secondary development of the constructed model using DEFORM-3D software,a GH710 material library was constructed,and a finite element model of GH710 turbine disc for hot rotary forging was established.It guides the development of the GH710 turbine disc hot rotary forging process.The main research contents and conclusions are as follows:By using Gleeble-3500 thermal simulation experiments,the stress-strain curve for GH710 was determined.GH710 microstructure evolution and deformation behavior at high temperature have been explored with SEM and EBSD microstructure analysis.According to the results,the flow stress for GH710 is very sensitive to temperature and strain rate changes,and its value decreases with an increase of temperature or an increase of strain rate.There are two types of dynamic recrystallization mechanisms at work in the alloy:discontinuous dynamic recrystallization（DDRX）and continuous dynamic recrystallization（CDRX）.Among them,DDRX dominates.At the same time,based on the DDM theory and the Prasad instability criterion,the GH710 hot processing map was established,and the hot working process window of the GH710 was determined:1343K-1363K/0.03s^-1-0.3s^-1and 1393K-1413K/0.01s^-1-0.3s^-1.By introducing the dislocation density model and critical strain model,a piecewise constitutive model of flow stress of GH710 is established.Through the error analysis of the piecewise constitutive relationship model,the correlation coefficient（R）between the predicted value of the model and the experimental value is 0.988,and the absolute average error（AARE）is 6.94%,which means high prediction accuracy.At the same time,the average grain size model of dynamic recrystallization of GH710 was constructed.By comparing the experimental and calculated values,it was found that R was 0.974 and AARE was only 5.83%.Based on the constructed model and combined with the secondary development technology of DEFORM-3D,the GH710 material library was constructed.Based on the DEFORM-3D platform,a coupled model of hot rotary forging and conventional forging finite element was established and numerical simulation was carried out.The results show that in the process of hot rotary forging,the blank presents a vortex flow along an axis perpendicular to the axial section,and the flow velocity decreases from the rim to the wheel core.It is the most difficult to fill the hub of the turbine disc,the filling speed on the outside of the hub is higher than that on the inside,and the filling height is uneven.After the hot rotary forging of the turbine,the disc is completed,the overall equivalent strain distribution is relatively uniform,complete dynamic recrystallization occurs in all parts,and the grains are fine and uniform.In addition,the peak value of the isothermal forging forming load of the turbine disc is about 3.65 times that of the hot rotary forging,and the equivalent strains of the upper surface,side surface,and axial center area of the hot rotary forging blank are all larger than those of the isothermal forging.The maximum strain of the hot rotary forging is 9.75,the maximum strain of isothermal forging is only3.75.After hot rotary forging,the fully dynamic recrystallization area of the turbine disc accounted for 96.74%,and the average grain size of DRX was only 1.1μm.In contrast,the proportion of fully dynamic recrystallization in conventional isothermal forging is only 80.60%,and there is incomplete dynamic recrystallization in the hub.