A Universal Criterion for Plastic Yielding of Metallic Glasses with a $(T/T_g{)}^{2/3}$ Temperature Dependence

Room temperature ($T_R$) elastic constants and compressive yield strengths of $\sim 30$ metallic glasses reveal an average shear limit ${\gamma }_C=0.0267\pm 0.0020$, where ${\tau }_Y={\gamma }_{C}G$ is the maximum resolved shear stress at yielding, and $G$ the shear modulus. The ${\gamma }_C$ values for individual glasses are correlated with $t=T_R/T_g$, and ${\gamma }_C$ for a single glass follows the same correlation (vs $t=T/T_g$). A cooperative shear model, inspired by Frenkel’s analysis of the shear strength of solids, is proposed. Using a scaling analysis leads to a universal law ${\tau }_{CT}/G={\gamma }_{C0}-{\gamma }_{C1}(t{)}^{2/3}$ for the flow stress at finite $T$ where ${\gamma }_{C0}=(0.036\pm 0.002)$ and ${\gamma }_{C1}=(0.016\pm 0.002)$.

Figure 1

Experimental shear stress at yielding, ${\tau }_Y={\sigma }_Y/2$ vs shear modulus $G$ at room temperature for 30 bulk metallic glasses.

Figure 2

Experimental shear strain at yielding (${\tau }_Y/G$) vs $t=T/T_g$. Small open circles show results at room temperature on 30 alloys of varying $T_g$. Solid symbols show the $t$ dependence of ${\tau }_Y/G$ for various individual alloys as indicated. The reader is referred to the text for references and details.