Nanoindentation investigation on the creep mechanism in metallic glassy films

Abstract

a b s t r a c tUsing the magnetron sputtering technique, two metallic glassy films namely Cu 44.3 Zr 45.1 Al 10.6 and Cu 44.2 Zr 43 Al 11.3 Ti 1.5 were prepared by alloy targets. The minor Ti addition effectively induces excess free volume. Upon spherical nanoindentation, the creep behaviors of both films were studied at various peak loads. As the increase of peak load, the creep deformations became more severely in both samples. Interestingly, Cu-Zr-Al-Ti film crept stronger than Cu-Zr-Al at small-load holdings (nominal elastic regimes), whereas it is opposite at high-load holdings (plastic regimes). The creep characteristic could be intrinsically related to the scale variation of the shear transformation zone (STZ) with Ti addition. Statistical analysis was employed to estimate the STZ volume, which increased by 60% with Ti addition in the Cu-Zr-Al film. The finite element modeling indicated that STZs would be activated even at the minimum load we adopted. Higher activation energy of larger STZs in Cu-Zr-Al-Ti enables less flow units, which offsets the creep enhancement by the excess free volume with Ti addition. The deeper the pressed depth of the indenter, the more contribution of the STZ operation on creep deformation. In addition, experimental observation on the creep flow rates implies that STZ could be the dominating mechanism at the steady-state creep. This study reveals that STZ volume could also be important to the time-dependent plastic deformation in metallic glass, besides as a key parameter for instantaneous plasticity.

Revealing Nanoindentation Size-Dependent Creep Behavior in a La-Based Metallic Glassy Film

“…In this scene, the specimen dimension and intrinsic structure state is constant whilst creep behavior could be correlated with deformation zone beneath the indenter. The correlation between creep deformation and holding depth has also been widely reported in metallic glasses, where creep displacement was gradually increased with increasing holding depth [21][22][23][24]. Qualitatively, more excess free volume content generated at deep holding depths was generally suggested as the reason.…”

“…depth-facilitated creep displacement was qualitatively explained by more excess free volume generated at deep holding depth [21][22][23][24]. Here we do not intend to deny previous conclusions, however the structure agitation would not be decisive to the change of creep displacement at various holding depths, particularly for Berkovich nanoindentation.…”

“…Thus the increased creep displacement under spherical indenters could be attributed to the multiple effects of enlarged deformation volume, increased holding strain and more dramatic structural agitation. In previous reports, the holding depth-facilitated creep displacement was qualitatively explained by more excess free volume generated at deep holding depth [21][22][23][24].…”

“…For example, dislocation move is dominating in creep flow as m falls in the range between 0.1 and 0.3. In metallic glasses, free volume generation and annihilation, shear transformation zone (STZ) evolution and atomic diffusion (under elastic contact) are thought to be the possible creep mechanisms [23]. While the relationship between m and creep mechanism in metallic glass is still inconclusive.…”

On the Room-Temperature Creep Behavior and Its Correlation with Length Scale of a LiTaO3 Single Crystal by Spherical Nanoindentation

“…In comparison to conventional creep measurements, nanoindentation has merits in that it is convenient, time-saving, and accurate, particularly for small-dimension and brittle materials [9,10]. Notwithstanding the unavoidable influence of thermal drift, which greatly hinders high-temperature mechanical investigations, nanoindentation has been widely adopted to explore the time-dependent plastic deformation of materials at room temperature [11][12][13][14][15]. In the authors' previous work [16], the room-temperature creep behavior and its correlation with structure orientation of a LiTaO 3 single crystal were revealed by nanoindentation with a standard Berkovich indenter.…”