Phase relations and stabilities at 900 °C in the U-Fe-Si ternary system

A systematic study of the U-Fe-Si ternary system was carried out in the whole concentration range, by means of scanning electron microscope observations, associated with energy dispersive X-ray spectroscopy analyses and X-ray powder diffraction measurements performed on as-cast and annealed samples. At 900 °C, the phase diagram is characterized by the existence of nine ternary compounds: U2FeSi3 with the AlB2-type, UFe2Si2 with the ThCr2Si2-type, U3Fe2Si7 with the La3Co2Sn7-type, U2Fe3Si with the MgZn2-type, UFeSi with the TiNiSi-type, U1.2Fe4Si9.7 with the Er1.2Fe4Si9.7-type, U2Fe3Si5 with the Lu2Co3Si5-type, U6Fe16Si7 of the Mg6Cu16Si7-type and UFe5Si3 with its own type of structure. Two intermediate solid solutions, U2Fe17−xSix (3.2 < x < 4) structurally related to the Th2Ni17-type and UFe12−xSix (1 < x < 3) structurally related to the ThMn12-type are formed and two extensions of binaries into the ternary system, UFexSi2−z−x (0 < x < 0.2) and UFexSi1−x (0 < x < 0.05) are observed. The homogenous ranges are formed by Si/Fe mechanisms of substitution. Analyses on as-cast samples revealed the formation of two additional ternary phases which were found to be stable only at high temperature, UFe1−xSi2 with x = 0.8 and a novel ternary compound with a 18(1)U:59(1)Fe:23(1)Si estimated atomic ratio.