Bulk-metallic glasses (BMGs) are a class of structural materials with many attractive processing features such as the ability to be processed into parts with fine features, dimensional precision, and repeatability; however, their fracture behavior is complex and size-dependent. Previous work has shown that BMGs can display strong size effects on toughness, where multiple mechanisms on different length-scales, e.g., crack bridging and bifurication, shear band spacing and length, can significantly affect the properies. This length-scale dependence on the fracture toughness has importance not only for advancing the understanding of fracture processes in these materials, but also for the potential future applications of BMGs, such as for microdevices. Here, using in situ scanning electron microscopy (SEM), we report on notched micro-cantilever bending experiments to address the lack of data regarding fracture properties of BMGs at the microscale. Sudden catastrophic propagation of shear bands resulted in failure for these specimens at stress intensities much lower than the bulk material, which may be due to a lack of extrinsic toughening mechanisms at these dimensions. This is explored further with post mortem SEM and transmission electron microscopy (TEM) analysis of the fractured beams while the fracture toughness results are verified using finite element modeling. The excellent agreement between model and micro cantilever beam bending experiments suggests that the intrinsic fracture toughness of Vitreloy 105, 9.03±0.59 MPa.m½, is being reported for the first time.
Bibliographical noteFunding Information:
The authors would like to acknowledge the Medtronic Restorative Therapies Group leadership for financial support of this research. D. Sorensen would also like to thank Mr. Brandon Van Leer and Dr. Jan Ringnalda of Thermo Fischer Scientific for helpful sample preparation advice, Mr. Peter Yurek of Medtronic for performing the x-ray diffraction experiment, Mr. Brian Leigh of Medtronic for performing the ICP-OES analysis, and Ms. Margaret Flury of Medtronic for careful proofreading of this manuscript. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. ROR was supported by the Office of Science , Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05CH11231 . DK acknowledges funding by the European Research Council under grant number 771146 (TOUGHIT).
- Bulk-metallic glasses
- Fracture toughness
- Length-scale dependence
- Micro-cantilever testing