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The strengthening mechanism of composite carbide (Ti,V)C enhanced Ni-based coatings was discussed by combined calculations and tests to obtain the influence mechanism of the microstructure and properties. The first principle was used to calculate the microstructure, formation energy, mechanical properties, anisotropy, and electronic properties of composite ceramic phase (Ti,V)C. It explored the effect of changes in Ti and V content on the properties of composite carbides. The influence mechanism of different Ti/V ratios on the performance and organization of coatings was analyzed by experiments to clarify the evolution process of the molten pool at different contents. The properties and crystal parameters of the composite phase greatly changed with increased V. The recombination of covalent bonds was an important reason for the increased hardness of the composite carbide. TiC with low Gibbs free energy precipitated preferentially at the solidification stage of the molten pool. The subsequent VC tended to form (Ti,V)C composite carbides with TiC as heterogeneous nucleation sites. When powder ratio Ti:V = 3:1, the hardness and wear resistance of the coating were better than those reinforced by single carbide TiC through hardness and friction wear tests. The difference in grain morphologies in the coating was the main reason for the change in coating performance. Research results provide a theoretical reference and basis for preparing composite carbide-reinforced coatings by laser cladding.

Abstract The microstructure of the cladded layers consisted of carbide particles and primary Fe 3 C blades in pearlite-ledeburite matrix. The addition of V into the cladded layer increased the volume percentage of carbide particles and led to the formation of relatively fine (Ti,V)C complex carbides with uniform distribution in the matrix, while the volume percentage of the primary Fe 3 C phase decreased. With increasing the weight percentage of V in the cladding layers, the microhardness and wear resistance of the cladding layers increased which was due to the increase in volume percentage of (Ti,V)C complex carbides and the strengthening effect of the matrix by V. The addition of V up to 5 wt.% to the two passes Fe-Ti-C cladding layer increased the hardness from 51 to 62 HRC. The wear weight loss decreased by about 60%. The predominant wear mechanisms of the cladded samples were separation of carbides and adhesive wear. In the cladded layer containing higher vanadium content, the separation of carbides decreased and lower adhesive wear was seen. [ABSTRACT FROM AUTHOR]

(Ti,V)C-Ni composite was sintered using ultrafine (Ti,V)C solid-solution powders prepared by mechanically alloying a Ti-V alloy/graphite powder mixture. The (Ti,V)C-Ni powders were sintered to full density at 1400 °C, which is significantly lower than that required for the conventional liquid-phase sintering of TiC-Ni or Ti(CN)-Ni powders. The examination of linear shrinkage curve during sintering revealed that the consolidation of the (Ti,V)C-Ni composite proceeds in three distinct steps. Firstly, it shrinks by the solid-state sintering. Afterwards, it expands by CO gas evolution. Finally, Ni melt penetrates into the pores between carbide particles during the liquid-phase sintering. The fracture toughness values of the (Ti,V)C-Ni composite were notably higher than those of TiC-Ni or even Ti(CN)-WC-Ni composites. The improved fracture toughness of the (Ti,V)C-Ni composites is believed to originate from the solid-solution effect of TiC and VC in addition to the lack of core/rim structure, which is common in Ti(CN)-WC-Ni composite. [ABSTRACT FROM AUTHOR]