Effect of TiC content on the microstructure and wear performance of in situ synthesized Ni-based composite coatings by laser direct energy deposition

Abstract

To reveal the effect of content and size of in situ synthesized TiC on phase compositions, microstructure, defects, and mechanical properties of matrix composites in detail, a series of Ni-based composite coatings were fabricated by direct energy deposition. The titanium (Ti) + Ni-coated graphite (C) contents in composite powder are 5, 10, 20, 30, 40, and 50 wt%, respectively. With the increase of Ti and C elements, the phases firstly change from γ–Ni, [Fe–Ni] solid solution, CrB, Cr7C3 to [Fe–Ni] solid solution, CrB, Cr7C3, TiNi2 TiC, TiB2, and finally to TiNi, Cr3C2, Fe2Ti, TiC, TiB2 under the competitive interaction between solute concentration and Gibbs free energy. The volume fraction and relative diameter of the TiC reinforcements are increased gradually to 28.06 % and 2.866 μm, respectively. The dispersed TiC particles are found at the grain boundary and refine the grains. The microhardness is increased from 608.41 ± 6.25 HV0.3 to 1075.11 ± 27.94 HV0.3 due to the combined effect of fine-grain strengthening, solid solution strengthening, and the second phase strengthening. The volume loss was significantly reduced when the relative diameter of TiC is larger than 2.2 μm. Moreover, the wear mechanism was transformed from adhesive wear to abrasive wear and ultimately to fatigue wear. In addition, the transverse and longitudinal cracks were also observed, limiting the application of the fabricated coatings.