Fatigue endurance limit and crack growth behavior of a high-toughness Zr61Ti2Cu25Al12 bulk metallic glass

Abstract

a b s t r a c tWe report the fatigue damage behavior of a Zr 61 Ti 2 Cu 25 Al 12 (ZT1) bulk metallic glass (BMG), which was known to have a record-high fracture toughness. The ZT1 exhibits the highest fatigue endurance limit among all BMGs, with a normalized fatigue limit of r a = 440 MPa (in four-point bending at a loading ratio of 0.1), or $0.27 of its tensile strength. The crack-growth resistance in the stress/life tests arises from crack-tip plastic shielding due to prolific shear-banding, as well as deflected crack path following a ''zigzag'' pattern. The relation between the range of stress intensity factor (DK) and the crack-growth rate (crack extension per cycle, da/dN) was also determined. ZT1 shows a fatigue threshold, DK th , of 2.8 MPa p m, which appears to be related to the onset of shear band nucleation. Three distinct regimes of fatigue crack growth were observed, with different slopes in the da/dN-DK curve, attributable to different micromechanisms. In the Paris regime, each fatigue striation on fracture surface is generated by a number of loading cycles, rather than by a single loading cycle. In general, the DK th of a BMG approximately scales with its fracture toughness. At different levels of DK, shear bands appear to play different roles, either facilitating or blunting the crack growth.

Cyclic cryogenic pretreatments influencing the mechanical properties of a bulk glassy Zr‐based alloy

“…The multiple shear bands near the fatigue fracture surface show a curved progress along various branches, also detectable in the vicinity of the unstable crack propagation area. This observation indicates increased shear band branching and multiple shear band sliding, which results in massive crack tip blunting and deceleration of stable crack growth in the fatigue zone of Zr‐based BMG alloys …”

Effect of Shot Peening on Mechanical Behavior of Zr-Based Bulk Metallic Glasses under Monotonic and Cyclic Loading Mode

“…3(e)) samples is composed of cracks, striation-like and smooth-like region. In addition, the P region of the as-cast sample also possesses staircase-like fracture feature, which is a common characteristics of BMGs with excellent fatigue performance 3,6) . As shown in Fig.…”

“…Bulk metallic glasses (BMGs) have been considered as potential structural materials due to their superior strength, high elastic limit and excellent corrosion resistance [1][2][3][4] . However, the poor fatigue behavior and plasticity of BMGs limit their engineering application, which remains a great challenge to the materials [5][6][7] .…”

Bulk Metallic Glasses as Structural Materials: A Review

“…However, the poor result can be attributed to two factors. First, the very poor fatigue resistance is specific to the composition of Vitreloy 1 and other compositions, such as Zr 52.5 Cu 17.9 Al 10 Ni 14.6 Ti 5 (Figure ), Zr 61 Ti 2 Cu 25 Al 12 , and Pd 79 Ag 3.5 P 6 Si 9.5 Ge 2 , have good fatigue resistance with σ fat / σ UTS in the range of 0.24–0.27 when tested under similar four‐point bending conditions . Moreover, some Fe‐, Co‐, Ni‐, Cu‐, and Ti‐based BMG compositions have been tested in tension–tension fatigue, also with R = 0.1, and all were found to have σ fat / σ UTS ≥ 0.25 .…”