New Class of Plastic Bulk Metallic Glass

Abstract

An intrinsic plastic Cu(45)Zr(46)Al(7)Ti(2) bulk metallic glass (BMG) with high strength and superior compressive plastic strain of up to 32.5% was successfully fabricated by copper mold casting. The superior compressive plastic strain was attributed to a large amount of randomly distributed free volume induced by Ti minor alloying, which results in extensive shear band formation, branching, interaction and self-healing of minor cracks. The mechanism of plasticity presented here suggests that the creation of a large amount of free volume in BMGs by minor alloying or other methods might be a promising new way to enhance the plasticity of BMGs.

Nanoindentation investigation on the creep mechanism in metallic glassy films

“…Here, the same effect of Ti addition would be concluded indirectly from the smaller-sized veinpattern fracture morphology. The SEM observations implies an enhanced ductility in Cu-Zr-Al film with Ti addition [20], which was consistent with Chen's [12]. What is more, the thinner smooth region indicates a relatively weaker resistance to the plastic shearing in Cu-Zr-Al-Ti film.…”

“…2(b). In the bulk sample, Ti addition on Cu-Zr-Al metallic glass effectively increased the density of shear bands during plastic deformation [12]. Here, the same effect of Ti addition would be concluded indirectly from the smaller-sized veinpattern fracture morphology.…”

“…With this in mind, creep behaviors of Cu-Zr-Al and Cu-Zr-Al-Ti Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea metallic glassy films were investigated in the present work. The minor Ti addition was confirmed to effectively increase free volume content while not changing the intrinsic parameters such as Poisson's ratio or elastic modulus [12]. The STZ volumes of both films were carefully estimated in nanoindentation based on a popular statistical method.…”

“…Additionally, free volume is another important atomic-level feature which can intrinsically control plasticity [9][10][11]. By adding just 2% Ti, plasticity of a Cu-Zr-Al metallic glass can be greatly enhanced due to the induced excess free volume [12]. The creation and annihilation of free volume could sustain the homogeneous creep flow at high temperature [13] or/and nanoscale [14].…”

An index of shear banding susceptibility of metallic glasses

“…If we were able to neglect the sample ends effects in the mechanical tests, the intervention of shear band propagation would be dominantly determined by the stress gradient induced by the intrinsic heterogeneous structure of MGs [1,54,55]. This is supported by the fact that MGs with pronounced free volume concentration [56] shows extraordinary plasticity by shear band multiplication. By introducing heterogeneous structure like secondary dendrite phases to intervene in the propagation of shear bands, even tensile ductility [57e59] can be designated in MG composites.…”