Phase equilibria in Er–Zr–Ni system at 800 С in ErNi–Zr–Ni region

Abstract

The isothermal section of the Er–Zr–Ni phase diagram in the ErNi–Zr–Ni region at 800 °С has been studied by means of X-ray phase and structural analyzes and energy-dispersive X-ray spectroscopy. The mutual solubility of the components Er, Zr and Ni at 800 ° С is insignificant: Zr dissolves up to 3 at. % Er and practically does not dissolve Ni; Ni practically does not dissolve Er and Zr; Er dissolves up to 13 at. % Zr and practically does not dissolve Ni. The existence of the binary compounds Er 2 Ni 17 , ErNi 5 , ErNi 4 , α -Er 2 Ni 7 , ErNi 3 , Er 0,98 Ni 2 , ErNi, ZrNi 5 , Zr 2 Ni 7 , ZrNi 3 , Zr 8 Ni 21 , Zr 7 Ni 10 , ZrNi and Zr 2 Ni has been confirmed in ErNi–Zr–Ni region. The following solid solutions of substitution based on the binary Er–Ni and Zr–Ni compounds were detected: Er 2- x Zr x Ni 17 (0≤ x ≤0,16; str. type Th 2 Ni 17 ); Er 1- x Zr x Ni 5 (0≤ x ≤0,63; str. type CaCu 5 ); Er 1- x Zr x Ni 4 (0≤ x ≤0,30; str. type PuNi 4 ); α –Er 2– x Zr x Ni 7 (0≤ x ≤0,05; str. type Er 2 Co 7 ); Er 1- x Zr x Ni 3 (0≤ x ≤0,18; str. type PuNi 3 ); Er 0,98- x Zr x Ni 2 (0≤ x ≤0,34; str. type TmNi 2 ); Er 1- x Zr x Ni (0≤ x ≤0,5; str. type), Zr 1- x Er x Ni 5 (0≤ x ≤0,30; str. type AuBe 5 ); Zr 2- x Er x Ni 7 (0≤ x ≤0,14; str. type Zr 2 Ni 7 ); Zr 7- x Er x Ni 10 (0≤ x ≤0,18; str. type Zr 7 Ni 10 ); Zr 1- x Er x Ni (0≤ x ≤0,32; str. type CrB); та Zr 2- x Er x Ni (0≤ x ≤0,30; str. type Al 2 Cu). Other binary compounds don’t dissolve any significant amount of the third component. One ternary compound Er x Zr 1- x Ni 2 (0,12≤ х ≤0,24) with the narrow homogeneity range at 800 o C occurs in the system. It crystallizes in the cubic MgCu 2 type of structure. It’s crystal structure has been refined for Er 0 , 17 Zr 0 , 83 Ni 2 composition using powder X-ray diffraction data: MgCu 2 str. type, Fd- 3 m space group, Z = 8, а = 6,987 (5) Å, R І =0,0915 for 8 independent reflections, І о > 2σ (І о ). The ternary compound Er x Zr 1- x Ni 2 (0,12 ≤ х ≤ 0,24) coexists with the solid solution Er 0,98- x Zr x Ni 2 (0 ≤ x ≤ 9,5) (СТ TmNi 2 ). The morphotropic row of cubic Laves phases MgCu 2 → TmNi 2 – a defect superstructure of the MgCu 2 type with doubled a -lattice parameter has been defined along the pseudo-binary “ZrNi 2 ”–Er 0 . 9 8 Ni 2 cross section. Keywords: ternary system, phase equilibria, intermetallic compounds, crystal structure.