Fatigue properties for micro-sized Ni-P amorphous alloy specimens

Fatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantilever-beam-type with dimensions of 10 × 12 × 50 μm³ prepared by focused ion beam machining. Notches with a depth of 3 μm were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN approx. 1.3 × 10^-8 ΔK^1.16 and da/dN approx. 3.7 × 10^-8 ΔK^0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to a decrease in effective stress intensity factor range ΔK_eff, by the effect of crack closure.