Effect of the Cu and Ni content on the crystallization temperature and crystallization mechanism of La–Al–Cu(Ni) metallic glasses

Peiyou Li

doi:10.1063/1.4942040

Abstract

The effect of the Cu and Ni content on the crystallization mechanism and the crystallization temperatures of La–Al–Cu(Ni) metallic glasses (MGs) was studied by differential scanning calorimetry (DSC). The experimental results have shown that the DSC curves obtained for the La–Al–Cu and La–Al–Ni MGs exhibit two and three crystallization temperatures, respectively. The crystallization temperatures of the La–Al–Cu and La–Al–Ni MGs result from the merging and splitting of thermal events related to the corresponding eutectic atomic pairs in the La72Cu28 and La81.6Al18.4 MGs, and La72Ni28 and La81.6Al18.4 MGs, respectively. In addition, Al- and Ni-containing clusters with weak or strong atomic interaction in the Al–Ni atomic pairs strongly affect the crystallization mechanism and thus the crystallization temperature of La–Al–Ni MGs. This study provides a novel understanding of the relation between the crystallization temperature and the underlying crystallization mechanisms in La–Al–Cu(Ni) MGs.

Highlights

The conventional way of characterizing the thermal stability of metallic glasses (MGs) is to determine the crystallization temperature (Tx) using a thermal analyzer.[1,2] A higher crystallization temperature indicates a higher stability of the MG, which implies that it is more difficult for the disordered structure to crystallize
This study provides a novel understanding of the relation between the crystallization temperature and the underlying crystallization mechanisms in La–Al–Cu(Ni) MGs
The following two assumptions were made in order to determine the relation between the multi-step crystallization temperature and the crystallization of disordered microstructures containing corresponding eutectic atomic pairs in La–Al–Cu(Ni) MGs: (1) The use of a wide range of eutectic compositions favors the formation of disordered microstructures when the solution with a binary eutectic composition is rapidly solidified by being cooled down from a temperature above Tl to a temperature below Tg, and (2) the deep eutectic composition is significantly distant from the composition of a range of intermetallic compounds with high melting temperatures

Summary

Introduction

The conventional way of characterizing the thermal stability of metallic glasses (MGs) is to determine the crystallization temperature (Tx) using a thermal analyzer.[1,2] A higher crystallization temperature indicates a higher stability of the MG, which implies that it is more difficult for the disordered structure to crystallize. Multi-step crystallization reactions in MGs can be studied by differential scanning calorimetry (DSC) and lead to distinct features in the DSC curves, for MGs with an amorphous phase separation. When studying multi-composition alloys, Kündig et al.[3] found that the crystallization of the La27.5Zr27.5Cu10Ni10Al25 alloy can be described as a merging of the crystallization of the La53.5Al21.5Cu18Ni7 and Zr56.5Al25Cu4.5Ni14 alloys, and this can be seen in the results of the DSC scan. Olofinjana and Tan[1] found that the first major exothermic peak they observed in the DSC curve obtained for the Gd30Zr25Al25Co20 alloy is close to the exothermic peak observed for the Gd55Al25Co20 alloy, while the second major exothermic peak is close to the exothermic peak observed for the ternary Zr55Al25Co20 alloy. The observed heat of mixing was positive when mixing the main atomic pairs (13 and 9 kJ·mol–1 when mixing the La–Zr and Zr–Gd atomic pairs, respectively), both pairs may yield negative heat values when mixed with others (e.g., the La(Zr)-Al, La(Zr)-Cu, La(Zr)-Ni atomic pairs, or the Zr(Gd)-Al, Zr(Gd)-Co atomic pairs).[1,3]

Methods

Results

Discussion

Conclusion