Approaching the melting temperature: There regimes in the non-isothermal crystallization of Ce68Al10Cu20Co2 bulk metallic glass revealed by nanocalorimetry

Abstract

Nanocalorimetry is an ideal candidate for revealing the crystallization of metallic glass in a wide temperature range attributing to its ultrafast heating rate and ultrahigh sensitivity. In this study, in situ preparation of Ce68Al10Cu20Co2 (at.%) metallic glass was realized by the nanocalorimetry. By the subsequent reheating at the rates from 500 to 40,000 K/s, the crystallization in a wide temperature range was demonstrated. The crystallization activation energy and Avrami exponent are calculated with the aid of the Kissinger and Johnson-Mehl-Avrami (JMA) equations to reveal the temperature-dependent nucleation and crystal growth behavior in the undercooled liquid, where three crystallization regimes are identified. At low temperature, the crystallization occurs with constant activation energy. In an intermediate temperature range, the crystallization is controlled by crystal growth with a reduction of activation energy. At temperatures approaching Tm, an increased activation energy resulting from the thermodynamic driving force dominates the nucleation-controlled crystallization. This study provides a novel strategy to reveal the crystallization behavior in the undercooled liquid from Tg to Tm and to demonstrate the transition from growth-controlled crystallization to nucleation-controlled one with the decrease of undercooling.