材料期刊网

The role of mu phase in a second generation directionally solidified Ni-base superalloy during high temperature creep has been characterized in the present work. A large amount of blocky mu phase enveloped by thick gamma'-film is found at the grain boundaries and in the vicinity of primary MC carbides after heat treatment. However, the creep-rupture properties of the alloy are not affected by the presence of the blocky p, phase at 760-1070 degrees C under a stress of 120-850 MPa. By the investigation of creep microstructure at 975 degrees C/255 MPa, it is found that the thick gamma'-film plays a pivotal role in toughening the grain boundaries and the interfaces between the mu phase (or carbides) particles and the matrix, and preventing the formation of cracks. Meanwhile, during high temperature creep, M(23)C(6) carbides are continuously coarsening with the dissolution of the p. phase particles and MC carbides, especially at the grain boundaries. The poor interface cohesion strength between such large M(23)C(6) carbides and the gamma matrix at the vertical segments of the directionally solidified grain boundaries leads to the final creep failure of the present alloy. (C) 2010 Elsevier B.V. All rights reserved.