X-ray diffraction investigation of the ternary systems V-Cr-B, Nb-Cr-B, and Mo-Cr-B

Summary

The binary compound Cr₅B₃ has a tetragonal structure with the lattice constants a=5.472±0,003, c=10.098±0.006 Å, and c/a=1.845. The phase equilibria in the systems V-Cr-B, Nb-Cr-B, and Mo-Cr-B at 1400°C have been established. In the system V-Cr-B, the continuous solid solutions VB₂-CrB₂, V₃B₄-Cr₃B₄, and VB-CrB have been found; the compound Cr₅B₃ dissolves up to 20 at.% V and the compound V₃B₂ dissolves up to 15 at. %Cr. In the system Nb-Cr-B, the maximum solubility of Cr in the compounds NbB₂ and Nb₃B₂ is 15 and 25 at.%, respectively. The maximum solubilities of a third component in the borides of the system Mo-Cr-B are: 17 at.% Mo in CrB₂, 16 at.% Mo in Cr₃B₄, 40 at.% Mo in CrB, 48 at.% Mo in Cr₅B₃, 6 at.% Mo in CrB₂, and 10 at.% Cr in Mo₂B. In the systems V-Cr-B and Mo-Cr-B, ternary phases with CuAl₂ type structures have been found (the lattice constants are a = 5.188 ±0.004, c=4.318±0.003 Å, and c/a=0.832 for the composition V_0,150−20Cr_1.85−1.80B, and a=5.215−5.245±0.003 and c=4.352−4.383±0.003Å for Mo_0.24−0.39Cr_1.76−1.61 B). The ternary phase (Mo, Cr)₃B₂ has a U₃Si₂ type structure (29–40 at.% Mo, 31−20 at. %Cr, 40 at.% B;'a=5.825−5.774±0.003 and c=3.115−3.082±0.002 Å).