Comparison of Semisolid Microstructure Evolution of Wrought Nickel Based Superalloy GH4037 with Different Solid Fraction

The research on semisolid metal forming of Ni-based superalloys is limited because of the difficulties in preparing semisolid billets. Traditional methods for fabricating semisolid billets are SIMA and RAP. In order to decrease the processing procedures, a new method called semi-solid isothermal treatment of wrought superalloy (SSITWS) was used to fabricate semisolid billets in this paper. In order to get the optimal parameters to fabricate Ni-based GH4037 semisolid billets, the effects of isothermal temperature and soaking time on microstructure evolution were investigated. The isothermal temperature ranges from solidus to liquidus, and the soaking time ranges from 10min to 60min. The results show that near-globular grains can be obtained only in the semi-solid state with appropriate solid fractions. When the solid fraction was high, the shape of grains was irregular and the average size of grains was large and inhomogeneous. When the isothermal temperature reached 1350°C, spherical grains appeared, and many small intragranular liquid droplets existed. During the appropriate isothermal temperature range, from 1350°C to 1380°C, the shape of solid grains was globular and the size of solid grains was homogeneous. At the same time, the size of the grains and the roundness of the grains increased with the increasing of isothermal temperature.