Fatigue Properties for Micro-Sized Ni-P Amorphous Alloy Specimens

Abstract

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 cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m 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 ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, 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 adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.

Fatigue and fracture of a Ni–P amorphous alloy thin film on the micrometer scale

“…Fatigue tests were carried out at a frequency of 10 Hz, using a constant load amplitude (Δ P /2, where Δ P = P max − P min ) of 2 mN and stress ratios, R (where R is given by minimum load ( P min )/ maximum load ( P max ) applied over the fatigue cycle), of 0.1, 0.3 and 0.5, respectively. This fatigue test condition was determined from previous research 21 . Although the crack length was not directly measured in this machine, the change in specimen compliance was monitored during testing.…”

“…This fatigue test condition was determined from previous research. 21 Although the crack length was not directly measured in this machine, the change in specimen compliance was monitored during testing. Crack initiation was, therefore, determined by monitoring the specimen compliance.…”

“…A mechanical testing machine that can apply both static and cyclic loads to micro‐sized specimens has been developed, 15 and the effects of specimen size on fatigue and fracture investigated. This was completed using Ni–P amorphous alloy, micro‐sized cantilever beam specimens approximately 1/1000th the size of ordinary‐sized specimens 16–21 . This material has hardly any intrinsic defects and has been used as hard‐disk substrates.…”

“…This was completed using Ni-P amorphous alloy, micro-sized cantilever beam specimens approximately 1/1000th the size of ordinary-sized specimens. [16][17][18][19][20][21] This material has hardly any intrinsic defects and has been used as hard-disk substrates. In addition, there are no grain boundaries in the material and the mechanical properties are considered to be isotropic.…”

Synchrotron Radiation and Instrumented Indentation Studies of Compressive Plastic Deformation in Zr-Based Bulk Metallic Glasses

“…The recent development of bulk metallic glasses (BMGs) and amorphous-nanocrystalline composites has renewed interest in their potential as structural materials [1,3]. It has been confirmed that some metallic glasses have a unique combination of various properties and are suitable for many applications [4]. However, mechanical behavior and prediction of failure in BMGs at temperatures below the glass transition temperature Tg are still under active investigations.…”