Creep behavior of conventional and Nb-modified as-cast MAR-M246 superalloy

Considering the lower cost of Nb and its chemical similarity to Ta, this work investigated the effect of complete replacement of Ta by Nb (in at.% basis) in MAR-M246 Ni-based superalloy for the automotive turbocharger applications. Conventional and Nb-modified polycrystalline MAR-M246 superalloys were prepared through vacuum induction melting and investment casting from commercial raw-materials. Creep tests were performed on the as-cast alloys in air, at 800 ?C (475/500/550 MPa), 900 ?C (300/350/400 MPa) and 1000 ?C (150/200/ 225 MPa). Additional creep tests were carried out at 900 ?C/350 MPa under high vacuum conditions to verify effects of oxidation on the creep behavior of the alloys. Both alloys presented similar creep behavior at 800 ?C. At 900 ?C and 1000 ?C, the conventional alloy has shown better properties associated with less creep damages in the bulk and near the surface regions. Both alloys have a better creep life in high vacuum which revealed an important role of oxidation on the creep damage mechanisms of these alloys. The lower creep properties of Nbmodified alloy at T > 800 ?C should be primarily associated with higher internal diffusivity in this alloy compared to the conventional one, leading to faster oxidation and microstructure degradation during the high temperature creep.

Automated summary

This study investigated the complete replacement of Ta by Nb in MAR-M246 Ni-based superalloy and found that the conventional alloy exhibited better creep properties at 900℃ and 1000℃. Both alloys showed longer creep life under high vacuum conditions, with oxidation playing an important role in the creep damage mechanisms of the alloys.