On the thermal stability of electrodeposited Ni-matrix-nanocomposite films reinforced with Ag-coated SnO2 nanowires

Ni-matrix-nanocomposite films were produced by constant-current electrodeposition from a sulphamate bath. The composite consisted of a disordered array of Ag-coated SnO2 nanowires grown onto a substrate by chemical vapour deposition, around which the Ni matrix was electrodeposited. The thermal stability of the films was analysed by non-isothermal annealing at up to 600 °C and isothermally at 300 and 500 °C for 10 h, at high vacuum (10− 7 to 10− 6 mbar). Pure Ni films were also analysed for comparison purposes. The microstructural evolution of the samples was characterised by means of X-ray diffraction and scanning electron microscopy assisted by electron backscatter diffraction. The composite showed higher thermal stability, evidenced by an increase of only 70% in its average grain size after annealing at 500 °C, against the 300% observed for the pure Ni films, as a result of pinning of the matrix's grain boundaries by the Ag-SnO2 phase. Moreover, it retained its random crystallographic orientation, while Ni samples evolved from a < 100 > towards a < 111 > fibre texture due to surface energy minimisation.