Influence of Solidification Parameters on the Microstructure and Properties of DZ125 Superalloy Castings

Abstract:

In this paper, the influences of withdrawal rates and mold heater zone temperature on the microstructures and the properties of heat treated castings were investigated. Results show that a better aligned grain structure and a much higher thermal gradient can be obtained in castings prepared by “high superheat” technique. Moreover, with elevating of withdrawal rates and mold heater zone temperature, the dendrite structures and size of γ′ phase are refined; dendrite structures and size of γ′ phase are larger in thicker zone. With the increase of withdrawal rates, γ+γ' eutectic fractions decreases but the micro-segregation decreases initially and then increases. With elevating of heating zone temperature, the γ+γ' eutectic fraction reduces and micro-segregation becomes severe except Ta. After heat treated, the dendrite structures of the castings become ambiguous and the γ′ phase prepared with various solidification parameters have no obvious difference. The properties of castings prepared with different withdrawal rates are almost the same, but that prepared with high thermal gradient has a better high temperature rupture life.

Key words:Ni-based superalloy; directional solidification; withdrawal rate; high superheating; micro-segregation; property