Hot Deformation Characteristic And Processing Maps Of Spray Formed GH742y Alloy

Spray formed GH742y alloys as important material of turbine disk arewidely used in the aerospace industry. Due to the high alloying, deformationduring hot working process is difficult. The hot deformation characteristics,including the influence of deformation conditions on the flow stress and theevolution of the microstructure mechanism, were studied using the methods ofphysical modeling. Establishment of the constitutive equation and hot processingmaps is a theoretical guidance for practical production and practical applicationvalue.Isothermal compression of GH742y alloy has been conducted on Gleebe-1500D hot-simulator at the deformation temperature ranging from1030℃to1120℃, the strain rate ranging from0.01s^-1to10s^-1and the strain rangingfrom20%to70%. According to the experimental data, the true stress-true straincurve of GH742y alloy during hot compressive deformation was established andthe change of stress with deformation condition was analyzed from true stress-true strain curves. The results showed that the flow stress of GH742y alloyincreases with decreasing temperature and with increasing strain rate, meanwhilethe curve belongs to the type of dynamic recrystallization.The constitutive equation of GH742y alloy during hot deformation has beenestablished based on hyperbolic sine equation of Arrhenius type. Comparing peakstress with the experimental value on the different deformation condition andusing error analyses we found that the established constitutive equation canobjectively explain the characteristics of GH742y alloy.The results of OM, SEM and TEM analyses for GH742y deformed underdifferent deformation conditions show that it is easy to occur for dynamicrecrystallization in the high temperature and large strain. Meanwhile, dislocationdensity and dynamic recrystallization nucleation rate increases with the increase of strain rate. It leads to recrystallized-grain-size decrease. Based on the materialwork hardening rate theory, the model of recrystallized grain size and therelationship between critical strain and Z parameter are established for sprayformed GH742y alloy.Based on dynamic materials model （DMM） theory, processing maps forGH742y alloy under the different deformation conditions are finished.Considering both processing maps and microstructure in different areas afterdeformation, the instability area and stability area of GH742y alloy processingmaps can be confirmed. Instability area corresponds to deformation temperatureranging from1030℃to1100℃, strain rateof10s^-1. However the energydissipation rate is lower than20%and section rheological instability phenomenain this area. Under the deformation condition of1090℃and0.1⁰.01s^-1, easilyoccur to DRX and recrystallized grain size is small and uniform distribution.Appropriate deformation parameters are found to be1090℃and0.01s^-1basedon present investigations.