Oxidation Mechanism of Ni-0.5Y Microcrystal CoatingSputtered by Magnetron at 1 000 ℃

The isothermal and cyclic oxidation behaviors of bulk pure nickel and its Ni-0.5Y microcrystal coating sputtered by magnetron at 1 000 ℃ in air were studied. The scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the structures of the coating and the NiO oxide films. The laser Raman spectrum was also used to measure the stress level in NiO films formed on bulk nickel and the coating. It is found that the Ni-0.5Y microcrystal coating has lower oxidation rate, and the grain size of NiO formed on Ni-0.5Y coating is also relatively smaller than that formed on bulk nickel. Meanwhile, the compressive stress level of oxide film formed on Ni-0.5Y coating was lower than that formed on bulk nickel, and the high temperature plasticity of oxide film was much improved in coating case. The improvements of anti-oxidation properties of the sputtered Ni-0.5Y coating are due to the microcrystal structure and yttrium.