Effect of thermo-mechanical processing on microstructure and creep properties of the foils of alloy 617

The effect of rolling and annealing on the microstructure and high temperature creep properties of alloy 617 were investigated. Two types of foil specimens with different thickness reductions were prepared by thermo-mechanical processing. Recrystallization and grain growth were readily observed at specimens annealed at 950 and 1100 degrees C. The uniform coarse grains increase resistance against creep deformation. The grain size effect in creep deformation was dominant up to 900 degrees C, while dynamic recrystallization effect became dominant at 1000 degrees C. Dynamic recrystallization was observed in all the creep deformed foils, even though some specimens had already been (statically) recrystallized during annealing. Steady state creep rates decreased with increasing annealing temperature in the less rolled foils. The apparent activation energy Q(app) for the creep deformation increased from 271 to 361 kJ/mol as the annealing temperature increased from 950 to 1100 degrees C. (C) 2009 Elsevier B.V. All rights reserved.