The influence of Mg on creep properties and fracture behaviors of Mar-M247 superalloy under 1255 K/200 MPa

Abstract

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 were investigated in this study. The results of quantitative statistical analyses showed that when Mg microadditions up to 50 ppm were made, the MC carbides located at grain boundaries (designated GB MC) were significantly refined and spheroidized and the number of MC carbides decreased. In addition, the M 23 C 6 carbides present on GBs dramatically increased with increasing Mg contents up to 50 ppm, and the creep resistance was enhanced under the test condition of 1255 K/200 MPa. However, the creep performance of a Mar-M247 superalloy containing 80 ppm Mg deteriorated due to the formation of an extremely large amount of MC carbide and a decrease in the number of M 23 C 6 carbides at GBs. The cracks mainly initiated and propagated along GBs in both 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 present creep condition, the optimal Mg microaddition to a Mar-M247 superalloy should be 30 to 50 ppm.

The Role of Magnesium in Superalloys—A Review

“…Bor et al [22][23][24] observed that in MAR-M247 nickel based alloy, 0.008% Mg increased the number of MC on grain boundary, which significantly decreased creep rupture life and elongation of the alloy. effect of Mg on impact toughness was reported which is shown in Figure 5, which is possibly due to the decrease in interdendritic Laves eutectic ( Figure 6) and the refinement of interdendritic segregation of Nb and Ti, which allowed shorter homogenization cycle.…”

“…However, the properties were still better than the alloy containing negligible amount of Mg (0.0001% Mg). Bor et al [22][23][24] extensively worked on the effect of Mg on creep characteristics, fracture mechanism and carbide characteristics of MAR-M247, a Ni-base superalloy under 1255K/200 MPa and 1033K/724 MPa conditions. They observed that under the former testing condition 0.005% Mg refined and spheroidized MC carbide at GB, which enhanced the creep properties, whereas 0.008% Mg addition increased the number of MC at GB, which significantly decreased rupture life and elongation.…”

“…The studies indicated that Mg is a surface-active element and segregation of Mg takes place at the grain boundaries and the interphases like /carbide and / [45,46]. The segregation of Mg at the interfaces and interphases in turn accounted for the surface-active characteristic of Mg and hence its high propensity for segregation to interfaces and interphases [22]. Mg formed an enriched layer of Mg surrounding the carbide and might influence the transport of carbon and carbide forming elements.…”

“…Mg formed an enriched layer of Mg surrounding the carbide and might influence the transport of carbon and carbide forming elements. This resulted in an isotropic growth of carbides during solidification and eventually led to the refinement and spheroidization of MC carbides both at the grain boundary and within the grain interior [4,[22][23][24]. The spheroidization resulted from Mg addition improves the stress distribution state at grain boundary thus decreases the possibility of wedge crack at the grain boundary [17].…”

Effect of Ultra-high Magnesium on SKS51 Liquid Steel Cleanliness and Microstructure

“…[1][2][3][4][5][6][7][8] The trace Mg in steel is not only a good deoxidizer and desulfurizer, but also has many metallurgical functions such as modifying and refining inclusions, [3][4][5] refining and spheroidizing carbides. [6][7][8] It is worth mentioning that the current research on Mg metallurgy is limited to the study of trace magnesium on steel metallurgy. The research on the effect of ultra-high Mg on steel metallurgy is still in blank field.…”