Effect of heat treatment on superplastic response of powder-consolidated nickel-base superalloy IN 100

Abstract

Superplastic deformation of samples of the powder-consolidated nickel-base superalloy IN 100 was carried out at 1311 K. Before deformation the specimens were annealed at 1473 K (above the γ′-solvus) to reduce the dislocation density since the material had initially been consolidated in the range 1348–1388 K (below the γ′-solvus) and consisted of a partially recrystallized structure of γ- and γ′-grains. After annealing the matrix was dislocation free and contained an almost uniform distribution of γ′-cubes. Specimen microstructures were examined after deformation in the strain rate range 3 × 10⁻⁵ to 3 × 10⁻³ s⁻¹. After testing at the higher strain rates a high dislocation density was observed within the grains and extensive grain-boundary cavitation had occurred. At the slowest strain rate, cavitation was not so severe and the overall dislocation density was much lower and varied from grain to grain. The γ′/γ morphology changed significantly during superplastic deformation. The microstructural changes provided evidence both for deformation by slip and diffusion at the top end of region II (the region of optimal superplasticity) and for grain rotation at the lowest strain rates.