Structural relaxation and shear softening of Pd- and Zr-based bulk metallic glasses near the glass transition

Understanding of the Structural Relaxation of Metallic Glasses within the Framework of the Interstitialcy Theory

“…With the appropriate choice of parameters, Equation (7) can be used for the calculation of g rel -dependence, as shown by the red solid/dashed curves. It is seen that, overall, there is quite acceptable correspondence between experimental and calculated shear modulus relaxation data [62], indicating the validity of the approach assumed by Equation (7). It is to be noted that the relaxation time near T g ≈ 560 K of glassy P d 40 Cu 30 N i 10 P 20 calculated with Equation (6) is about 2900 s, and it is this large relaxation time that determines the shear modulus hysteresis shown in Figure 4 [62].…”

“…This behavior is soon changed into an increase of the shear modulus, but the latter remains significantly smaller than that in the course of the initial heating. Such a big hysteresis turns out to be a characteristic feature of MGs [62]. The obvious reason for it is the big underlying relaxation time [62] (see below Equation (6) and the related discussion).…”

“…Such a big hysteresis turns out to be a characteristic feature of MGs [62]. The obvious reason for it is the big underlying relaxation time [62] (see below Equation (6) and the related discussion).…”

“…While far below the glass transition temperature T g this state is kinetically unachievable, near T g it can be reached from opposite sides at reasonable times, leading to different signs of property changes [60]. In particular, this is manifested in the relaxation of the shear modulus G, as illustrated in Figure 2, which gives the temperature dependence of G for bulk glassy P d 40 Cu 30 N i 10 P 20 measured upon linear heating and cooling at the same rate together with the shear modulus G eq in the metastable equilibrium determined by prolonged isothermal tests at different temperatures [61,62]. The temperature T pc in this figure is interpreted as the Kauzmann pseudocritical temperature, i.e., the lowest temperature at which the state of the supercooled liquid is still possible (see [61] for details).…”

“…It is to be noted that the relaxation time near T g ≈ 560 K of glassy P d 40 Cu 30 N i 10 P 20 calculated with Equation (6) is about 2900 s, and it is this large relaxation time that determines the shear modulus hysteresis shown in Figure 4 [62]. It should be also emphasized that the Maxwell relaxation time τ m = η/G (η is the shear viscosity) at T = T g is about 20 s, and therefore, the Maxwell viscoelasticity does not constitute a proper basis for the understanding of relaxation phenomena in MGs, even near the glass transition (see [62] for more details). …”