Rafting microstructure during creep of the MC2 nickel-based superalloy at very high temperature

Directional coarsening of the single-crystalline nickel-based superalloy MC2 has been investigated by means of tensile creep tests at 1100 degrees C. Two specific specimen geometries were designed in order to generate a variety of stress and strain states. Different coarsening microstructures are observed: N- and P-type classical rafting but also coarsening oriented 45 degrees away from the load axis. The comparison of microstructure maps with the local mechanical state evaluated by finite element calculations shows that the 45 degrees directional coarsening appears in case of very high cumulated strain values (above 10%), independent of the stress sign. Transmission electron microscopy investigations show that the dislocation microstructure is similar in both N-type and 45 degrees coarsened areas. (C) 2009 Elsevier B.V. All rights reserved.