Creep deformation and mechanisms in Haynes 230 at 800 °C and 900 °C

Creep was studied in Haynes 230, a material candidate for the very high temperature reactor's intermediate heat exchanger, at 800 degrees C and 900 degrees C. This study focused on the differences between the behavior at the two elevated temperature, and using the microstructure, grain boundary serrations and triple junction strain concentrations were quantitatively identified. There was significant damage in the 900 degrees C samples and the creep was almost entirely tertiary. In contrast, the 800 degrees C sample exhibited secondary creep. Using an Arrhenius equation, the minimum creep rate exponents were found to be n approximate to 3 and n approximate to 5 for 900 degrees C and 800 degrees C, respectively. The creep mechanisms were identified as solute drag for n approximate to 3 and dislocation climb for n approximate to 5. Strain concentrations were identified at triple junctions and grain boundary serrations using high resolution digital image correlation overlaid on the microstructure. The grain boundary serrations restrict grain boundary sliding which may reduce the creep damage at triple junctions and extend the creep life of Haynes 230 at elevated temperatures. (C) 2013 Elsevier B.V. All rights reserved.