Microstructures, mechanical properties and tribological behaviors of NiAl-based composite coatings with various addition of Nb

The microstructures, mechanical properties and tribological behaviors of the NiAl-based composite coatings with various addition of Nb were investigated. Particularly, the coatings registered a typically fine lamellar morphology and a dense microstructure, of which the microhardness increased with the Nb content increasing. Moreover, the coatings with various Nb contents registered different tribological properties and wear mechanisms at different test temperatures. The wear mechanisms of the coatings transferred from serious abrasive wear (NA1), brittle fracture accompanied with abrasive wear (NA2), abrasive wear (NA3) to serious fracture and abrasive wear (NA4) with the increment of Nb content at room temperature. At 400 °C, the coatings with low contents of Nb (NA1, NA2) possessed low friction coefficients but high wear rates due to the plastic deformation and micro-cutting. However, the coatings with high contents of Nb (NA3, NA4) possessed higher friction coefficients but low wear rates due to the reinforcement and anti-wear effect of metal Nb, and the wear mechanism was dominated by adhesive wear. At 800 °C, the coatings possessed the wear mechanism of slight abrasive wear, and a series of bimetallic oxides, e.g. AgNbO₃ and NiNb₂O₆ generated through the high-temperature tribochemical reactions. The synergistic lubrication of oxides was responsible for the lower COFs of the coatings at 800 °C. But higher wear rate of the NA1 coating was ascribed to the low hardness and adhesive strength due to the low content of metal Nb. As a whole, metal Nb could observably enhance the wear resistance of the coatings at different temperatures.