Phase transformation of MoSi2 phase in MoSi2/Mo5Si3 eutectic alloy containing Nb

Role of ternary solute element Nb on the C40 --> C11b phase transformation of the MoSi2 phase in MoSi2/Mo5Si3 eutectic alloys which occurs during heat treatment is discussed in this paper. In the case of stoichiometric MoSi2, a mixture of C40 and C11b phases can be prepared by low-pressure plasma sp raying method, in which phase transformation from the metastable C40 to sta ble C11b is recognized during heating at around 800 degrees C. It is found that the MoSi2, phase in an as-cast eutecric MoSi2/Mo5Si3 alloy with 8.5 at %Nb consist only of metastable C40 phase. The transformation from C40 to C1 1b in this alloy does not occur by heating up to 1200 degrees C but a porti on transforms into C11b by heating at 1400 degrees C. It is shown that the Nb concentration in C40 phase is higher than that in C11b phase in this all oy, which must be relevant to the observed transformation behavior.