The 400℃ And 550℃ Isothermal Sections Of The Phase Diagram Of The La-Ni-Fe Ternary System*

The 400℃ and 550℃ isothermal sections of the phase diagram of the La-Ni-Fe ternary system investigated by powder X-ray diffraction (XRD), differential thermal analysis (DTA), optical microscopy and scanning electron microscopy(SEM) techniques.The 400℃ isothermal section which was restricted to the Fe-rich and La-rich parts of the La-Ni-Fe ternary system consists of 4 single-phase regions, 5 two-phase regions and 2 three-phase regions. The 4 single-phase regions are: a (Fe), y (La), T (La7Ni3), and v (LaNi) . The 5 two-phase regions are: a + y, a + T , a + v , y + T , and T + v . The 2 three-phase regions are: a + y + T , and a + T + v . The 550℃ isothermal section which was restricted to the Fe-rich and Ni-rich parts of the La-Ni-Fe ternary system consists of 8 single-phase regions, 13 two-phase regions and 6 three-phase regions. The 8 single-phase regions are: a (Fe), 3 (Ni), n (LaNi5), i(La2Ni7), k (LaNi3), A (La7Ni,6), u(La2Ni3), and v (LaNi). The 13 two-phase regions are: a+{3, a + n., a + t , a + k , a + X , a + u , a + v , P + n, n+i, i + k , k + X , X + u , and n + v . The 6 three-phase regions are: a + {3 + n., a + n+v, a+i+K, a + k + X , a+X + u, and a + u + v.At 550°C, the maximum solid solubility of Ni in Fe is about 5at.%Ni; the maximum solid solubilities of Fe in Ni, LaNi5, La2Ni7, LaNi3, La7Nii6, La2Ni3, and LaNi are about 75.5at.%Fe, 10at.%Fe, 5at.%Fe, 4at.%Fe, 1.5at.%Fe, 3at.%Fe and 2at.%Fe, respectively. The maximum solid solubility of La in a -Fe and ? -Ni is about 1.5at.%La and 2at.%La, respectively.It is proved that the compound in La-Ni system is La7Nii6, not LaNi2 at 550°C. The La3Ni is not exited at 400°C. The existence of any ternary compounds has not been observed in the two isothermal sections.