The effects of Mg microaddition on the mechanical behavior and fracture mechanism of MAR-M247 superalloy at elevated temperatures

The effects of microadditions of Mg on the mechanical behavior and fracture mechanism of MAR-M247 superalloy were investigated in this study. The micr ostructural observations and image analysis showed that a Mg microaddition ranging from 30 to 80 ppm significantly changed the primary MC carbide char acteristics and inhibited the scriptlike carbide formation. After a 80 ppm Mg addition, the elongation measured at 1172 K increased over 3 times found that for the Mg-free MAR-M247 superalloy. The creep life and rupture elong ation of the MAR-M247 superalloy with 80 ppm Mg was also improved up to 3 t o 5 times that of the alloy without Mg during a 1033 K/724 MPa creep test. The fracture analyses demonstrated that cracks were mainly initiated and pr opagated at the interface of scriptlike MC carbides in the Mg-free MAR-M247 superalloy at elevated temperatures. The Mg microaddition effectively refi ned and spheroidized these coarse carbides so that a change in the crack in itiation occurred from the carbide/matrix interface to that along the gamma -gamma' eutectic. Interfacial analysis using Auger electron spectroscopy il lustrated that Mg segregated to the interface of the MC carbide/matrix, cau sing a change in the morphology and interfacial behavior of the carbides. T his improvement contributed to a prolonged rupture life and upgraded the mo derate temperature ductility of the MAR-M247 superalloy.