Spinodal Decomposition of High Nickel Fe-Mo-Ni Ternary Alloy and Precipitation Region of Ni<SUB>3</SUB>Mo Phase

Phase decomposition and precipitation of the Ni3Mo phase in high Ni Fe-Mo-Ni ternary alloys were investigated by means of transmission electron microscopy and hardness measurement. The results obtained are as follows: In Fe-14 at%Mo-14 at%Ni alloy, a modulated structure can be seen at the aging temperature below 823 K. At 773 K, a Mo-rich zone of the modulated structure changes into a bcc η phase with the progress of decomposition. A stable λ phase ((Fe, Ni)2 Mo) appears after precipitating the η phase. This aging process is analogous to the case of the Fe-20at%Mo alloy. At 673 K, the λ phase is directly formed in the interface of the Mo-rich zone and the Mo-poor zone. At 623 K, Ni3Mo phase precipitates in the Mo-poor zone of the modulated structure.The Ni3Mo phase is observed in Fe-2 at%Mo-Ni alloys containing more than 16 at%Ni and in Fe-14 at%Mo-Ni alloys containing more than 10 at%Ni. The precipitation region of the Ni3Mo phase at 623 K has been obtained as shown in Fig. 10.