Effect of deformation mode on hot ductility of a γ′ precipitation strengthened nickel-base superalloy

Disparity in hot ductility of a γ′ precipitation strengthened nickel-base superalloy, IN 738 LC, subjected to non-equilibrium heating and compressive and tensile stresses, was investigated. The alloy, which shows considerable hot ductility at temperatures ranging from 1160 °C to 1250 °C under compressive loading, exhibits zero ductility under tensile loading within this temperature range. The difference is attributed to the fact that while compressive loading permits plastic deformation in spite of non-equilibrium liquid phase dissolution of γ′ precipitates in the alloy, the occurrence of the liquation reaction results in inhibition of plastic deformation under tensile loading. Accordingly, while grain refinement through strain-induced dynamic recrystallization occurred under compressive loading, within the same temperature range, the formation of new grains was prevented under tensile loading. This behavior is crucial during high temperature processing of γ′ precipitation strengthened nickel-base superalloys.