Tensile and fatigue fracture mechanisms of a Zr-based bulk metallic glass
- PDF / 474,272 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 210 Views
The tensile and fatigue fracture behavior of Zr59Cu20Al10Ni8Ti3 bulk metallic glass was investigated. It was found that under tensile load the metallic glass always displays brittle shear fracture and the shear fracture plane makes an angle of T (⳱54°) with respect to the stress axis, which obviously deviates from the maximum shear stress plane (45°). Under cyclic tension–tension loading, fatigue cracks first initiate along the localized shear bands on the specimen surface, then propagate along a plane basically perpendicular to the stress axis. Tensile fracture surface observations reveal that fracture first originates from some cores, then propagates in a radiate mode, leading to the formation of a veinlike structure and final failure. The fatigue fracture processes of the specimens undergo a propagation stage of fatigue cracks followed by catastrophic failure. Based on these results, a tensile fracture criterion for bulk metallic glasses is proposed by taking the effect of normal stress into account. It is suggested that both normal and shear stresses affect the fracture process of metallic glasses and cause the deviation of the fracture angle away from 45°.
I. INTRODUCTION
Bulk metallic glasses (BMGs) have a unique combination of properties that makes them potentially attractive structural materials;1,2 however, the high strength of BMGs is often accompanied by remarkably little plastic deformation.3–12 To improve the mechanical properties of BMGs, several efforts have been made by different approaches, such as precipitation of nanoscale particles by partial crystallization13–15 and homogenous dispersion of insoluble particles or fibers as reinforcements.16–18 Another recently developed technique is to precipitate dendritic crystals in situ, which results in ductile BMG composites containing microsized particles.19,20 New BMG composites containing different reinforcements are being investigated and developed for potential industrial application. On the other hand, for the fabrication of the BMGs with excellent performance, it is necessary to reveal their basic deformation and fracture mechanisms. As is known, in crystalline materials, slipping, shearing, kinking, and twinning are important plastic deformation modes,21 and the yielding of most single crystals often a)
On leave from Shenyang National Laboratory for Materials Sciences, Institute of Metal Research, Chinese Academy of Science, Shenyang, 110016, People’s Republic of China. e-mail: [email protected] b) This author was an editor of the journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/jmr/policy.html. 456
http://journals.cambridge.org
J. Mater. Res., Vol. 18, No. 2, Feb 2003 Downloaded: 02 Dec 2014
follows the Schmid law. In general, single crystals will slide along the slip system with the largest Schmid factor; therefore the yield stress, the angle between slip bands and the stress axis can be calculated from t
Data Loading...
