Thermo-mechanical Degradation of NiCr Thin Film Subjected to Thermal Cycling

摘要

The thermo-mechanical degradation of NiCr films during thermal cycling was investigated in terms of microstructural and chemical changes to the surface. Thermal cycling was performed between room temperature and 200°C in thermally evaporated NiCr films on an Mn-Ni-Co-O substrate. Isothermal exposures were also performed as a control experiment. The sheet resistance of the NiCr films increased linearly (from 35 to 52 Ω/sq.) with a temperature difference of the thermal cycling, whereas the films subjected to isothermal aging increased only slightly, from 35 to 38 Ω/sq, After 300 thermal cycles at AT=175°C, cracks formed and proliferated on the coating surface, and local delamination occurred at the interfaces. XPS results showed that the intensity of a metallic peak at 574.0 eV decreased and that of the Cr oxide peak at ~577 eV increased with an increase of the thermal cycles. Consequently, the degradation of the NiCr films by accelerated thermal cycling stress was attributed to a proliferation of lateral surface cracks from thermally induced tensile stress compounded by surface oxidation, causing an increase in sheet resistance.