The Cr-Ni-V system

Abstract

The Cr-Ni-V system was investigated at 1100 ‡C using XRD, metallography, and energy dispersive chemical analysis of phases using scanning electron microscopy (SEM). The bcc α phase extends from the Cr-Ni binary to the V-Ni binary and has a maximum solubility of Ni in ternary α phase alloys of ∼12 at. %. A wide fcc γ phase field exists at the Ni corner. A ternary Σ phase (Σ₂) exists; it differs from the binary Ni-V Σ phase (Σ₁). The Σ₁ phase has a tetragonal unit cell with parameters almost double those of a normal Σ phase (Σ₂). Results indicate difficulty in achieving equilibrium states in alloys containing more than 30 at. % V and less than 15 at. % Cr even after 480 h annealing. The phase analysis of alloys annealed for 170 to 480 h suggests Σ₂ first forms through a ternary peritectic reaction to subsequently develop the Σ₁, phase by subsidiary reactions in those ternary alloys in the concentration range where Σ₁ is the stable phase. A tentative reaction scheme, consistent with the phase relations established at 1100 ‡C, is proposed.