On the fragility and thermomechanical properties of Mg–Cu–Gd–(B) bulk metallic glasses

Abstract

High glass-forming ability correlated with fragility of Mg-Cu(Ag)-Gd alloysIn this study, the viscous flow behavior and thermomechanical properties of Mg 65 Cu 25−x B x Gd 10 ͑x = 0 and 3 at. %͒ bulk metallic glasses ͑BMGs͒ in the supercooled liquid region have been investigated by using differential scanning calorimetry and thermomechanical analyzer. It has been found that the fragility of the supercooled liquid is reduced by the boron addition, thus, degrading the deformability. This conclusion is supported by the many other extracted parameters. Thus, even with much higher hardness, the B-additive Mg based BMG will be more difficult to be formed, which appears to be a negative factor in applying in the microforming or nanoimprinting industry.

Viscous Flow Behavior and Workability of Mg-Cu-(Ag)-Gd Bulk Metallic Glasses

“…The viscosity trend as a function of temperature of the current Mg-Cu-(Ag)-Gd BMGs is consistent with those for other Mg, Zr and Au BMGs [24][25][26][27] Fig. 3 The variation of the applied stress as a function of the measured strain rate for the three alloys tested under the isothermal condition at three load levels of 100, 300 and 500 mN.…”

Flow serration and shear-band viscosity during inhomogeneous deformation of a Zr-based bulk metallic glass

“…The viscosity value in Fig. 4 is about 1.1 Â10 4 -5.3 Â 10 5 Pa s, which is in a similar range as the viscosity value commonly measured from BMGs homogeneously deformed at low strain rates (10 À5 -1 s À1 ) and temperatures in or near the supercooled liquid region [16][17][18]27,28]. However, it is pointed out that compression tests in the current study were performed at room temperature which only corresponds to w0.47 -T g , which is well below the expected temperatures for homogeneous deformation in a BMG.…”

“…w f2 ¼ 5.05 Â 10 À32 m 3 /atom, the viscosity would increase by one order of magnitude. We want to mention again that the viscosities in various BMGs in or near the supercooled liquid region were usually measured by static or quasi-static mechanical tests (strain rates typically at 10 À5 -1 s À1 ) [18,34]. In contrast, shear band propagation is a dynamic process (strain rate > 10 3 s À1 in Fig.…”

“…On the other hand, shear localization has been suggested to be resulted from strain softening caused by viscosity drop from free volume creation/accumulation [13,14]. Only few studies were conducted to directly measure the viscosity of shear bands during inhomogeneous deformation of BMGs at room temperature [15], although there were substantial studies on the viscosity of BMGs at elevated temperatures during static or quasi-static homogeneous deformation [16][17][18]. To measure the viscosity during shear banding, parameters such as load, displacement and elapsed time during shear banding must be accurately obtained.…”

Tin-modified gold-based bulk metallic glasses

“…5a and b [20]. In addition, we observed that viscosity increases as increasing applied stress from 13 to 65 kPa.…”