Regularities of Metallurgical Reactions of Ti_{1 –n}${\text{Me}}_{n}^{{\text{V}}}$C_0.5N_0.5 Carbonitrides with the Ni–Mo Melt

Abstract

The influence of alloying TiC_0.5N_0.5 carbonitride by transition metals of Group V (V, Nb, and Ta) on the contact interaction mechanism with the Ni–25%Mo melt (T = 1450°C, τ = 1 h, rarefaction is 5 × 10^–2 Pa) is systematically studied by X-ray spectral microanalysis and scanning electron microscopy for the first time. It is established that the dissolution of single-type Ti_1 –n${\text{Me}}_{n}^{{\text{V}}}$C_0.5N_0.5 carbonitrides (n = 0.05) is an incongruent process (alloying metal and carbon preferentially transfer into the melt), and the relative rate and degree of incongruence of the dissolution process of carbonitrides in a series of alloying metals V–Nb–Ta vary nonmonotonically. An explanation for the discovered effects is proposed. The causal-effect relation between the initial composition of Ti_0.95${\text{Me}}_{{0.05}}^{{\text{V}}}$C_0.5N_0.5 carbonitride (the grade of the alloying metal) and composition of the Ti_{1 – n – m}Mo_n${\text{Me}}_{m}^{{\text{V}}}$C_x K-phase that is precipitated from the melt upon system cooling is analyzed. It is shown that the factor determining the composition of the forming K-phase is the ΔT factor (the degree of exceeding crystallization temperatures of carbide eutectics Ni/Me^VC over the crystallization temperature of the Ni/Mo₂C eutectic that is the lowest melting in these systems). The conclusion is argued that the interrelation between the initial carbonitride composition and the composition of the K-phase is a consequence of a microinhomogeneous structure of metallic alloys. It is shown that this interrelation is rather common and manifests itself in all studied systems irrespective of the type of alloying Group V metal and presence or absence of molybdenum in the melt.