Serrated flow behaviors of a Zr-based bulk metallic glass by nanoindentation

Abstract

Shock compression response of a Zr-based bulk metallic glass up to 110 GPa J. Appl. Phys. 108, 083537 (2010); 10.1063/1.3501044 Temperature-dependent shear band dynamics in a Zr-based bulk metallic glass Appl. Phys. Lett. 96, 061901 (2010); 10.1063/1.3309686Effect of high strain rates on peak stress in a Zr-based bulk metallic glass J. Appl. Phys.Instrumented nanoindentation tests were used to investigate the mechanical properties of Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 bulk metallic glass. The corresponding loading strain rates were ranged from 0.002 s À1 , 0.02 s À1 to 0.2 s À1 . Plastic flow of this material exhibited remarkable serrations at low strain rates and increasingly became weakening until disappearance with increasing indentation strain rate, implying strong rate sensitivity. A significant pile-up around the indents was observed through atomic force microscopy, which suggested a highly localized plastic deformation. Mechanism governing the deformation was tentatively discussed in terms of the increasing process of free volume with a negligible temperature rise under low strain rate, which well explained the declining trend of elastic modulus and hardness with an increase of indentation depth. V C 2014 AIP Publishing LLC. [http://dx.

Nanoindentation response of laser shock peened Ti-based bulk metallic glass

“…2(a) show that the size of the serrations increases while the number of the serrations decreases with the increase of h. The similar phenomenon was also found by Yang 14 on Au-based BMG and Cheng 15 on Zr-based BMG. To confirm the phenomenon at greater h, the nanoindentation tests with h final = 1000 nm were performed, as seen in Fig.…”

Plasticity improvement for dendrite/metallic glass matrix composites by pre-deformation

“…(5), the free volumes grow during the plastic deformation, which has been verified by experiments [20,21,[24][25][26] and modelings [23]. Thus, the annihilation rate is smaller than the creation rate upon deformation.…”

“…Recently, Ke et al reported [26] that the Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 BMG exhibited volume dilatation of up to 0.2% after compressive creep of the as-cast sample at a yield stress of 80%, and this phenomenon is attributed to the generation of a great amount of free volumes. The increased free volumes make the Young's modulus of the glass matrix decrease [20,24,25], resulting in the Young's modulus of the glass matrix and dendrites being approaching, since the crystalline dendrites have a lower Young's modulus than the glass matrix. The aim of this study is to investigate the contribution of matching the Young's modulus between the glass and dendrite phases to the plasticity of in-situ dendrite-reinforced MGMCs.…”

“…Based on the above micromechanisms, multiplication, branching, and deflection of the shear bands are crucial to improve the plasticity. The pre-deformation not only increases the free volumes in the glass matrix [12,[20][21][22][23][24][25], but also the dislocation density within the crystalline dendrites increases [15][16][17][18]. Recently, Ke et al reported [26] that the Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 BMG exhibited volume dilatation of up to 0.2% after compressive creep of the as-cast sample at a yield stress of 80%, and this phenomenon is attributed to the generation of a great amount of free volumes.…”

Testing effects on hardness of a Zr-based metallic glass under nanoindentation

“…For example, Xue et al [12] reported a positive strain rate dependence of the hardness and ascribed this correlation to the stronger strain rate softening effect under lower strain rates. There are also analogous inconsistent results, but the underlying mechanism has been rarely shed light on [13][14][15][16][17]. In addition, Bhattacharyya et al [6] demonstrated a lower strain rate sensitivity of the hardness under a higher peak-load, but the results of Ma et al [17,18] showed a much more positive rate sensitivity when the peak-load increased by 1 order of magnitude.…”