Structure and creep rupture properties of directionally solidified eutectic γ/γ′–α alloy

Abstract

A simple ternary γ/γ′–α alloy of nominal composition (wt-%) Ni–32Mo–6Al has been directionally solidified at 17 mm h⁻¹ and tested in creep rupture at 1073, 1173, and 1273 K. A uniform microstructure consisting of square-shaped Mo fibres in a γ + γ′ matrix was found despite some variation in the molybdenum and aluminium concentrations along the growth direction. Although the steady-state creep rate is well described by the normal stress–temperature equation, the stress exponent (12) and the activation energy (580 kJ mol⁻¹) are high. The rupture behaviour is best characterized by the Larson–Miller parameter where the constant equals 20.