Influence of Rhenium on the Grain Boundary Strength, Phase Evolution, and High Temperature Mechanical Properties of a Fine-Grain Nickel-Base Superalloy at 982 degrees C

Abstract

The influence of Re on the grain boundary (GB) strength, phase evolution, and 982 degrees C mechanical properties of fine-grain Mar-M247 superalloy 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 results of tensile and 982 degrees C/200 MPa creep tests showed that tensile properties and creep life both increase with an increase in Re up to a maximum at 3 mass%. The tensile and GB strength increased with increasing the number of fine GB carbides. The addition of 1 similar to 3 mass% 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 gamma' phase; (2) by increasing the strength of gamma matrix; and (3) by increasing the development of gamma' 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. It is noted that the GB carbide evolution and GB strengthening effect by addition of Re have not been reported in the nickel-base superalloy before. However, addition of greater amounts of Re, such as 5 mass% Re, causes deterioration of the tensile and creep properties due to the formation of P phases. [doi:10.2320/matertrans.M2011136]