Nucleation behavior of the primary FCC-Al phase in a Al86Ni10MM4 metallic glass

Abstract

The kinetics analysis of the heterogeneous nucleation behavior of primary FCC-Al in Al-based metallic glasses (MG) has been limited to a narrow temperature range below glass transition temperature due to the limited thermal test range available for conventional DSC (differential scanning calorimetry). Investigation of nucleation kinetics over wide temperature ranges has been a persistent challenge to clarify the kinetic competition between glass formation and nucleation of primary FCC-Al. To overcome this limitation, the Time-Temperature-Transition (TTT) diagram of primary FCC-Al in Al₈₆Ni₁₀MM₄ (MM: mischmetal) MG has been determined by thermodynamic calculations and nucleation delay time data measured at the high (near melting temperature) and low (near glass transition temperature) temperature region by Flash DSC (FDSC). By analyzing the break point of the increasing glass transition and crystallization temperatures resulting from annealing, the nucleation delay time of FCC-Al in the temperature range of 493 K to 513 K was determined. Quenching a molten Al₈₆Ni₁₀MM₄ MG at cooling rates over 33,000 K/s suppressed the formation of intermetallic phases, enabling the determination of the delay time of FCC-Al nucleation in the range of 750 K to 760 K from FDSC cooling curves by the additivity rule. Experimental delay time data, coupled with a statistical analysis on nucleation events during repeat runs observed at the cooling rate of 40,000K/s, provided valuable constraints on the assignment of kinetics parameters for the TTT diagram.