Tensile and high cycle fatigue tests of NiCo thin films

This paper represents the results of tensile and fatigue tests of NiCo thin films, to investigate the effect of size on mechanical properties. The "dog-bone" type Specimen with reduced section widths of 50 μm and 150 μm were fabricated on two 6 inch wafers using electro-plating process and MEMS processes. The NiCo film thickness of one wafer was 7.23 μm. The elastic moduli of the NiCo thin film specimens were about 183±4.1 GPa for the 50 μm specimens and about 148±8.4 GPa for 150 μm specimens. The ultimate tensile strengths for the 50 μm and 150 μm width specimens were 2431±87.8 and 2348±93.3 MPa, respectively. However, the difference between the tensile strengths of the specimens is low, at 3.3%. Fatigue tests were performed with 2 or 5 Hz in atmospheric air at room temperature under axial loading at a load ratio of R (=F_min/F _max) = 0.1 in a load-control until complete failure. Fatigue strength coefficients of the specimens with 50 and 150 μm width were 1785 and 1257 MPa, respectively. In addition, fatigue strength exponents of the specimens with 50 and 150 μm width were -0.0818 and -0.0629, respectively.