Effect of Ti microparticles on the microstructure and properties of Ni-Ti composite coating prepared by electrodeposition

In this study, Ni-Ti composite coatings were prepared using electrodeposition. Experimental results and COMSOL computer simulation revealed the effect of the Ti microparticles on the microstructure and properties of the Ni-Ti composite coating. The incorporated Ti microparticle lead to grain refinement, texture elimination which were correlated with the effect of current concentration and heterogeneous nucleation. Domains consisting of inner nano-grains and outer radial columnar grains were located around the Ti microparticles, where the Ti microparticles acted as seeds. This was closely correlated with the time-dependent plating conditions like current density and electric field lines during incorporation process of the Ti microparticles. Besides that, during the incorporation process of Ti microparticles, current density concentration on the “V”-shaped valley between closely neighboring Ti microparticles promote the presence of fine Ni grains, existing between but not belonging to the Ti microparticles. Selective deposition of Ni metal on Ti microparticle surface, local current density concentration and the aggregation of Ti microparticles were observable, contributing to the spatial heterogeneity of the microstructure. Compared with the pure Ni coating, the average hardness of the Ni-Ti composite coating increased from 2.91 ± 0.43 GPa to 3.98 ± 0.46 GPa, leading to the enhanced wear resistance. However, spatial heterogeneity of the hardness distribution was observed due to the heterogeneous microstructure of Ni-Ti composite coating, which confined the improvement of wear resistance.