Formation of a Nanocrystalline Structure upon Severe Thermomechanical Treatment and Its Effect on the Superplastic Properties of a Nickel Alloy with Nonisomorphic Second-Phase Precipitates

摘要

Severe thermomechanical processing of the Inconel 718 alloy has been shown to cause the formation of a nanocrystalline (NC) structure with an average grain size of 0.08 mu m. The processing includes discontinuous thermomechanical treatment by the scheme of multiaxial isothermal forging at low strain rates and step-wise decrease of the treatment temperature to 0.6 T_m. The thermal stability of the NC structure has been studied upon heating and superplastic deformation. It is established that the structure refinement to the NC state decreases the temperature threshold of the low-temperature superplasticity to 0.57 T_m (550 deg C).