Does the fracture toughness of bulk metallic glasses scatter?

Abstract

A method is introduced to determine notch toughness of bulk metallic glasses (BMGs). Through thermoplastic replication of Si molds, unprece-10 dented control in fabricating BMG toughness samples can be achieved and influences such as cooling rate, thermal history, residual stress, sample geometry, and notch precision are drastically reduced. For the 20 Zr 44 Ti 11 Cu 10 Ni 10 Be 25 BMG samples, we measured a notch toughness of 109 ± 3 MPa ffiffiffi ffi m p . Such a much smaller scatter than the previously reported suggests reliable properties of BMGs when thermoplastically formed.

Nanosecond pulsed laser irradiation induced hierarchical micro/nanostructures on Zr-based metallic glass substrate

“…Furthermore, very low thermal conductivity of MGs results in a high local temperature in the cutting region especially during high speed cutting. Thus, oxidation and crystallization of MGs may occur [20] which probably affect their amorphous performances [21,22], but this kind of effects is dependent of the properties and volume fraction of the crystalline phases [21][22][23] as well as the sample preparation and evaluation methods [24,25]. In addition, high local temperature will also increase the adhesion between the chip and tool, leading to the formation of built-up edge on the rake face, and thus affect the subsequent cutting process [16,26].…”

Bulk Mechanical Properties Testing of Metallic Marginal Glass Formers

“…Despite being most popular for samples with limited size, an indentation fracture test is not reliable for brittle materials because of the ill-defined crack arrest state that complicates analysis when compared to the rapid through-crack propagation of standardized tests [20,21]. This results in serious discrepancies in mechanical properties data obtained by indentation.…”

“…For example, previous fracture toughness measurements of Zr-based metallic glass obtained by three-point bending showed a large scatter in the data [20]. This is understood as a processing issue, 2 Journal of Metallurgy rather than a testing issue, and it is recognized that thermoplastic forming (such as spark plasma sintering) offers better control over sample thermal history to minimize processinginduced scatter [21]. Fracture toughness measurements of Fe-based metallic glasses have also been obtained by threepoint bending [6,18,19], but the test specimens and notch were nonstandard geometries that can cause errors.…”

Review on the Research and Development of Ti-Based Bulk Metallic Glasses

“…The cooling rate during the preparation process, the stress state, the impurity inclusions, the sample size, and the sharpness of notch/crack fabrication are all possible reasons. In order to reduce the extrinsic effect, Chen et al [197] proposed a novel sample preparation method for fracture toughness test via the thermoplastic forming of BMGs and Si photolithography. Using this strategy, they measured the notch toughness of 86 ± 3 MPa·m 1/2 for a Ti 41 Zr 25 Be 28 Fe 6 BMG.…”