Influence of Rhenium on the Mechanical Behavior and Fracture Mechanism of a Fine-Grain Superalloy at Elevated Temperatures

This study investigated the influence of rhenium on the mechanical behavior and fracture mechanism of a fine-grain Mar-M247 superalloy at elevated temperatures. Tensile test results showed that the addition of 3 mass% Re significantly improved the ultimate tensile strength and yield strength from room temperature to 760 degrees C. Creep test results showed that steady-state creep behavior dominated creep properties under the test condition of 760 degrees C/724 MPa. The steady-state creep rate and creep life of alloy with 3 mass% Re was reduced by 31% and prolonged by 63%, respectively, compared to alloy without Re. The improvement in tensile and creep properties in 3 mass% Re alloy was associated with a decrease in grain and gamma' size and an increase in strength of gamma/gamma' matrix. However, adding 4.5 mass% Re resulted in a decrease in the tensile and creep properties due to the formation of needle-like P phase in the grain interior. Fracture analysis demonstrated that during tensile and creep tests, cracks initiated and propagated along grain boundary in alloy without Re and containing 3 mass% Re alloy; however, in the alloy containing 4.5 mass% Re, cracks initiated and propagated along grain boundary and the P phase/matrix interface. Under the current tensile and creep conditions, 3 mass% Re was an optimal addition for casting a fine-grain Mar-M247 superalloy. [doi: 10.2320/matertrans.M2010299]