Mechanism of liquid-phase interaction between nanocrystalline composition (VC0.40О0.53–C)–C and titanium nickelide

The article considers the possibility of binding free carbon existing in the VC0.40O0.53–Cfree nanocrystalline composition to the carbide phase. This composition is obtained by plasma-chemical synthesis in a low-temperature nitrogen plasma. As a carbide former, titanium was used in the form of its nickelide TiNi, which has a melting point of 1310 °С. Experiments were carried out under vacuum sintering conditions involving the liquid phase at 1500 °C for 40 min. The data obtained in X-ray diffraction, scanning electron microscopy and energy-dispersive analysis were used to determine the phase composition and microstructural features of sintered samples. Liquid-phase interaction between the VC0.40O0.53–Cfree nanocrystalline composition and titanium nickelide, the content of which varied from 10 to 99 wt.%, was studied based on the results of experiments. It was shown that the content of Cfree and VC vanadium carbide increases with the simultaneously increasing TiC content as the TiNi mass content increases in the range of 10–90 wt.%. With a further increase in the titanium nickelide content to 99 wt.%, Ti3Ni4 and Ni3Ti nickelides are present after sintering. The content of free carbon increases to 88 wt.%, and the amount of TiC decreases to 5 wt.%. The data obtained in the course of the study were used to propose various schemes of processes occurring during the (VC0.40O0.53–Cfree)–TiNi liquid phase sintering. In particular, sintering involving the liquid phase proceeds in three stages including TiNi melting, refractory base dissolution, its reprecipitation in the form of TiCx and VCx carbides, and cooling of the resulting composition. It should be noted that the mechanism of liquid-phase interaction during vacuum sintering involving the liquid phase was developed on the basis of the laws presented in the paper by M. Gumenik.