Correlation between supercooled liquid region and crystallization behavior with alloy composition of La-Al-Cu metallic glasses

Abstract

Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La_86−x Al₁₄Cu _x (x=16 at%–20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%–19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu₁₃ through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La₆₆Al₁₄Cu₂₀ glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.