Very High Cycle Fatigue Characteristics of Zr-Base Bulk Amorphous Alloy in Rotating Bending

Abstract

In order to investigate very high cycle fatigue characteristics of the Zr 55 Al 10 Ni 5 Cu 30 (in at.%) bulk amorphous alloy, fatigue tests were performed in rotating bending at a frequency of 52.5 Hz with a stress ratio of R=-1. The test environment was in room atmosphere without any control of temperature nor humidity. The fatigue endurance limit σ w of the bulk amorphous alloy was about 700 MPa and the fatigue strength ratio σ w /σ B (fatigue endurance limit divided by the ultimate tensile strength) was found to be 0.38. Fracture surfaces of failed specimens were observed by scanning electron microscope (SEM). The fracture surface was separated into three typical regions; (1) multi-facet region, (2) stable crack propagation region and (3) instantaneous fracture region. The cracks took place on the specimen surface and fatigue striations were clearly formed in the stable crack propagation region on the fracture surface. A distinct boundary was observed between the stable crack propagation region and instantaneous fracture region. The instantaneous fracture region was covered by the dimple-type morphology. Vein-like patterns peculiar to the static fracture surface of amorphous alloys were also found in the edge region of the fracture surface. The fatigue fracture toughness of this bulk amorphous alloy was in the range of 20-29 MPa·m 1/2 .

Tensile strength and fatigue crack growth rate of chamfered and clamped A6061 friction weld joints

“…8. Schematic diagram of the fatigue crack growth specimen with a surface crack; M : bending moment, b : crack depth, 2a : crack length, d : shaft diameter [14] The stress intensity factor range (SIFR) of the crack, DK, may be evaluated using Equation (1) when the stress ratio, R = -1, as occurs in the cantilever rotary bending fatigue testing machine [14].…”

“…In addition, the research was conducted on the very high cycle fatigue characteristic of the bulk amorphous alloy of Zr 55 Al 10 Ni 5 Cu 30 (in at. %) by performing fatigue testing using cantilever rotary bending test with a frequency of 52.5 Hz and stress ratio of -1 [14]. The crack initiated on the surface of the specimen and fatigue fractures could be clearly observed in the zone of stable fatigue crack growth.…”

Statistical Duplex <i>S-N</i> Characteristics of Bulk Amorphous Alloy in Rotating Bending in Very High Cycle Regime

“…However, Young's modulus give a value of 147 GPa which is smaller than usual structural steels. Elongation of bulk amorphous alloy is only 0.29%, which suggests that the bulk amorphous alloy is a brittle material [12]. Fatigue Tests.…”

“…Here, the width of the multi-facet pattern in the short life region is larger than that in the long life region. This trend becomes more distinctive as the applied stress level is decreased [12]. This fact suggests that the crack takes place at a localized area in the long life region and this trend appears more markedly at the low stress level having the longer fatigue life.…”

“…Prof. Peker, Prof. Inoue and their co-workers reported that the Zr-Ti-Cu-Ni-Be bulk amorphous alloy could be obtained at cooling rate less than 10 K/s by a conventional copper-mold casting technique. Since this outstanding work, bulk amorphous alloys such as a thick bar with diameter up to several centimeters have been successfully fabricated [6][7][8][9][10][11][12].…”