Effection of alloying elements on microstructures of MX 246 and X 246A Ni3Al-based alloys

The effects of alloying elements on microstructure of two compositions of Ni3Al-based alloys, MX 246 and MX 246A have been studied in this article. The results show that starburst gamma-gamma' eutectic phases are large and their amount is about 18% in MX246. Majority NiZr and a little of ZrC are formed in the boundaries of gamma-gamma' eutectic phases. Microstructure at 1200 degrees C shows that NiZr phases have been melted completely, which cause the decrease of melting point gamma' of phases to about 1125 degrees C. With increasing alloying additions such as Mo and Hf, gamma-gamma' eutectic phases are dispersive, uniform, small, and their amount is decreased to about 4%. Carbides and borides are formed in MX246A. The volume fractions of the phases in MX246A and the chemical compositions of the phases have been quantitatively analyzed. The results show that carbides and borides are about 1.12% in MX246A and the main carbides are TiC, HfC and the borides are (Ni0.086Cr0.087W0.094Mo0.376Ti0.334 Hf-0.024) B-3(2). TEM observation results show that with increasing alloying element additions such as Mo and Hf, a lot of gamma/gamma' interface misfit dislocations are produced in the interface of gamma and gamma' phase and they are interacted with the nanometer gamma' particles. gamma' phases are all stable in MX246A at 1200 degrees C. The stability of gamma' phase is increased with the addition of Mo and HE In addition, there are many white spot phases which are mainly NiMo phases, and a little (NiMo)(6)C and (MoTi)(6)C gathering in some interdendrite areas.