Abstract
The influence of Re on the grain boundary (GB) strength and 982 ℃/200 MPa creep properties of fine-grain Mar-M247superalloy was investigated. Quantitative statistical analysis showed that an increase of Re content in Mar-M247 resulted in a decrease of the size, and an increase in the number of GB carbides. The GB strength increased with increasing the number of fine GB carbides. The results of 982 ℃/200 MPa creep tests showed that creep life increase with an increase in Re content up to a maximum at 3 wt.%. The addition of 1-3 wt.% Re reduced steady-state creep rates and postponed the onset of the acceleration stage in three ways: (1) by increasing the amount of primary cuboidal γ′ phase; (2) by increasing the strength of γ matrix; and (3) by increasing the development of γ′ raft. It also prolonged the duration of the accelerating creep stage by refinement and an increase in the number of GB carbides. The above mentioned factors resulted in a prolongation of creep life. However, addition of greater amounts of Re, such as 5 wt.% Re, causes deterioration of the creep properties due to the formation of P phases.
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