Thermal oxidation of Ni – 40 wt.% W and Ni – 50 wt.% W coated copper

ABSTRACT This work focuses on the oxidation behaviour of Ni-W electrodeposited coated copper, containing approximately 40 and 50 wt.% tungsten and having a thickness of about 15 µm. The oxidation kinetics of these materials were evaluated by performing isothermal oxidation tests in air, at different temperatures (from 550 up to 850°C) and for different durations (20 min up to 2 h). From the experimental curves of weight gain versus time, a parabolic oxidation pattern was obtained under the selected conditions and the oxidation rates were calculated and compared. The experimental results clearly indicate that the addition of tungsten resulted in a significant degradation of the oxidation resistance of the nickel matrix. Post X-ray diffraction analysis of the oxidised surfaces showed that the oxide film was composed of NiO, WO2, WO3, W3O8, NiWO4 and CuO (due to oxidation of the substrate). In addition, grain growth phenomena took place, as the amorphous structure shifted towards nanocrystalline and microcrystalline, which is indicated by the crystalline Ni peaks in the X-ray diffraction patterns.