Synthesis of (Cr,V)2(C,N) solid solution powders by thermal processing precursors

Abstract

The single-phase (Cr,V)2(C,N) solid solution powders were fabricated via carbothermal reduction-nitridation (CRN) processing technique. The effects of heat treatment temperature, nitrogen pressure and carbon proportion were experimentally studied in detail by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and thermal analysis. The chemical transformations of vanadium and chromium compounds were as follows: precursors → V2O3, Cr2O3 → Cr3C2, Cr2O3, (Cr,V)2(C,N) → (Cr,V)2(C,N). When the heat-treated temperature was below 1200 °C, chromium oxides didn’t completely react. However, higher temperature ∼1300 °C could not only lead to the segregation of some nitrides and carbon black, but also to the occurrence of fiber-bridged particles. The system nitrogen pressure over 0.03 MPa would cause a subtle transformation of (Cr,V)2(C,N) to VCrN2. When the carbon proportion was below 15 wt%, the oxides could not be completely reduced, while when the carbon proportion was above 15.5 wt%, some undesired carbides, like Cr23C6 and Cr3C2, would form. Ultimately, the homogeneously distributed pure-phase (Cr,V)2(C,N) spherical particles with the average size of ∼1.5 μm were obtained at the optimal conditions of the treatment of precursors at 1200 °C for 1 h with the nitrogen pressure of 0.03 MPa and carbon content of 15.5 wt%. The chemical composition of the solid solution with the optimal process could be drawn as (Cr0.85V0.15)2(C0.57N0.43). Thermal processing precursors method shows the advantages of lower synthesis temperature, shorter period and finer particles when comparing with the conventional preparations.