Cooling rate effect on Young's modulus and hardness of a Zr-based metallic glass

It is known that cooling rate can affect the atomic structure and thus may possibly affect the mechanical properties of metallic glasses (MGs). In spite of the considerable efforts on the cooling rate, its effect on the mechanical properties is controversial at the present time. In this study, we present a micromechanical study of the cooling-rate effect on Young's moduli and hardness of the cast bulks and melt-spun ribbons for a Zr55Pd10Cu20Ni5Al10 metallic glass. Using the classic nanoindentation method, the Young's moduli of the ribbon samples obtained at higher cooling rates were measured which appeared to be much lower than those of the bulk samples. However, through further experiments on slice samples cut from the as-cast bulks and finite-element (FE) analyses, we have clearly demonstrated that the measured difference in elastic moduli was mainly caused by the sample thickness effect in nanoindentation tests. To overcome such a confounding effect, microcompression experiments were performed on the as-cast and as-spun MG samples, respectively. Being consistent with the findings from nanoindentation, the microcompression results showed that the cooling rate, as ranging from ∼102 to ∼106 K/s, essentially has no influence on the Young's modulus and hardness of the metallic glasses.

Research highlights▶ The apparent reduction in the Young's moduli of the ribbon metallic glass relative to those of the bulk metallic glass, as measured using nanoindentation, has been proved simply caused by sample thickness. ▶ Cooling-rate independent hardness were attained. ▶ The insignificant influence of the cooling rate on the Young's modulus and hardness of the Zr-based MG implies that a faster cooling rate is needed for further research or the overheat temperature is not high enough to introduce any significant physical change in the glassy structure of the Zr-based MGs.