Hot Deformation Characteristics For Nickel-based Superalloy

The hot-working technology of the corrosion resistant Ni-based alloy N08028 which is applied in high acid gas oilfield is investigated. Since the thermoplastic at high temperature is weak and the thermal deformation zone of the 028 alloy is narrow, the hot extrusion is the only technology for the processing of the studied alloy. In the current work, the hot deformation behaviors at 1000℃-1200℃ are investigated by determining the process parameters of hot extrusion in combination with the help of analysis testing methods, e.g. optical microscopy(OM), scanning election microscopy(TEM) and transmisson electronic microscopy(TEM).The main conclusions are as follows:The strain-stress curve of the 028 alloy deformed at 1000℃-1200℃ indicates a typical dynamic recrystallization phenonmenon. With the elevating strain rate and decreasing deformation temperature,peak stress and steady stress increased while the recrystallized grain size decreased. A high deformation temperature and low strain rate will accelerate the dynamic recrystallization.By hot extrusion experiment, the deformation activation energy of the 028 alloy is determined, as 420.9kJ/mol. The correspondingly constitutive equations and expressions of model for dynamic recrystallization are given by,ε＝1.21669×1015[sinh(0.005912916⊙)]3.56exp(420886/RT) Xdrex=1-3xp[-0.21×(ε-εc/εp) 1.33]The maximum energy dissipation is related to the nucleation and growth of dynamic recrystallization. When the strain rate is high, the nucleation of dynamic recrystallization dominates the maximum energy dissipation. When the temperature is high, it is related to the growth of dynamic recrystallization. However, the maximum energy dissipation is related to both the nucleation and growth when both the temperature and strain rate of deformation are low. Besides, the unstable region which is related to the concentration of strain and precipitates can be observed when the alloy is deformed at low temperature and high strain rate.The optimum deformation parameters of the studied alloy can be obtained from the processing map. The initial optimum deformation parameters is 1200℃,10s-1 and finish ones is 1100,0.1s-1. When the alloy deformed under these conditions, the energy dissipation is reduced and the production efficiency is improved.