The influence of Mg on creep properties and fracture behaviors of Mar-M247superalloy under 1255 K/200 MPa

The effects of Mg microadditions on the high-temperature/low stress (1255 K /200 MPa) creep properties and fracture behavior of a Mar-M247 superalloy w ere investigated in this study. The results of quantitative statistical ana lyses showed that when Mg microadditions up to 50 ppm were made, the MC car bides located at grain boundaries (designated GB MC) were significantly ref ined and spheroidized and the number of MC carbides decreased. In addition, the M23C6 carbides present on GBs dramatically increased with increasing M g contents up to 50 ppm, and the creep resistance was enhanced under the te st condition of 1255 K/200 MPa. However, the creep performance of a Mar-M24 7 superalloy containing 80 ppm Mg deteriorated due to the formation of an e xtremely large amount of MC carbide and a decrease in the number of M23C6 c arbides at GBs. The cracks mainly initiated and propagated along GBs in bot h the Mg-free and Mg-containing Mar-M247 superalloys under 1255 K/200 MPa, and the finial rupture was caused by intergranular fracture. Under the pres ent creep condition, the optimal Mg microaddition to a Mar-M247 superalloy should be 30 to 50 ppm.