The Effect of Free Volume on the Crystallization of Al87Ni8Gd5 Amorphous Alloy

Galina Abrosimova,Ilia Sholin,Nikita Volkov,Valentina Chirkova,Aleksandr Aronin,Elena Pershina

doi:10.3390/met12020332

Abstract

The effect of free volume on the process of crystallization of an Al87Ni8Gd5 amorphous alloy is investigated. The deformation of the amorphous alloys leads to the formation of shear bands, which contain an enhanced free volume concentration. To retain the free volume the amorphous alloy was coated with a layer of a refractory metal. The structure of the Al87Ni8Gd5 alloy with a protective Ta coating was studied by X-ray diffraction and transmission electron microscopy methods. The fraction of the nanocrystalline phase formed in the amorphous samples with a protective Ta coating under annealing was found to be larger than that in the uncoated samples. The size of Al nanocrystals formed in the coated and uncoated samples is the same. A higher rate of crystal nucleation in the deformed amorphous samples with a protective coating is caused by a higher diffusion coefficient due to an enhanced free volume concentration.

Highlights

Amorphous–nanocrystalline alloys are materials with unique physical and chemical properties [1,2,3]
If a nanocrystalline structure is formed during deformation, the formation of nanocrystals begins in deformation bands and their vicinity [4,5,6,7]
The quenched ribbons of Al87Ni8Gd5 amorphous alloy were amorphous; no signs of crystalline phases were observed in the X-ray diffraction patterns and electron diffraction patterns

Summary

Introduction

Amorphous–nanocrystalline alloys are materials with unique physical and chemical properties [1,2,3]. Much work is devoted to the study of shear bands in amorphous materials [8,9,10,11] and changes in the structure in shear bands [12]. No obvious correlation between a shear band and a change in the density (free volume concentration) is observed. Investigations showed that there was a local region around shear bands in which deformation resulted in significantly larger atomic displacements than those in the surrounding matrix and in an enhanced free volume concentration. This region was called the shear transformation zone (STZ) [9,14]

Methods

Results

Conclusion