Solution heat-treatment of Nb-modified MAR-M247 superalloy

MAR-M247 superalloy has excellent mechanical properties and good oxidation resistance at elevated temperatures. Niobium is an element known as γ′ phase hardener in nickel-based superalloys, besides promoting homogeneous distribution of MC carbides. This work is inserted in a project that aims to evaluate the total replacement of tantalum by niobium atoms in MAR-M247 superalloy (10.2 Co, 10.2 W, 8.5Cr, 5.6 Al, 1.6 Nb, 1.4 Hf, 1.1 Ti, 0.7 Mo, 0.15 C, 0.06 Zr, 0.015 B, Ni balance—wt.%). Based on microstructural characterizations (SEM and FEG-SEM, both with EDS) of the as-cast material and heat-treated materials as well as utilizing Thermocalc simulations and experiments of differential thermal analysis (DTA), heat-treatment at 1260 °C for 8 h was chosen as an ideal condition for the solution of Nb-modified MAR-M247 superalloy. The hardness of as-cast and ideally solution treated materials was 390 ± 14 HV and 415 ± 6 HV, respectively.

► DTA and microstructure of MAR-M247(Nb) showed a good agreement with Thermocalc. ► An ideal condition for solution heat-treatment of MAR-M247(Nb) is 1260 °C for 8 h. ► It was an observed evidence of incipient melting in samples heat-treated at 1280 °C.