In situ visualization of Ni-Nb bulk metallic glasses phase transition

TL;DR

This study investigates the structural evolution and crystallization behavior of Ni-Nb bulk metallic glasses using in situ techniques, revealing surface crystallization phenomena, mechanisms, and nano-structure development during annealing.

Contribution

The paper introduces a comprehensive in situ analysis of Ni-Nb metallic glasses, highlighting surface crystallization at lower temperatures and proposing a new 2D-crystallization mechanism involving local surface phases.

Findings

Surface crystallization occurs below full sample crystallization temperature.

Primary crystallization starts with Ni3Nb phase formation.

Surface nano-structures can develop during annealing at sub-crystallization temperatures.

Abstract

We report the results of the Ni-based bulk metallic glass structural evolution and crystallization behavior in situ investigation. The X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-beam diffraction (NBD), differential scanning calorimetry (DSC), radial distribution function (RDF) and scanning probe microscopy/spectroscopy (STM/STS) techniques were applied to analyze the structure and electronic properties of Ni63.5Nb36.5 glasses before and after crystallization. It was proved that partial surface crystallization of Ni63.5Nb36.5 can occur at the temperature lower than for the full sample crystallization. According to our STM measurements the primary crystallization is originally starting with the Ni3Nb phase formation. It was shown that surface crystallization drastically differs from the bulk crystallization due to the possible surface reconstruction. The mechanism of Ni63.5Nb36.5 glass alloy 2D-crystallization was suggested, which corresponds to the local metastable (3x3)-Ni(111) surface phase formation. The possibility of different surface nano-structures development by the annealing of the originally glassy alloy in ultra high vacuum at the temperature lower, than the crystallization temperature was shown. The increase of mean square surface roughness parameter Rq while moving from glassy to fully crystallized state can be caused by concurrent growth of Ni3Nb and Ni6Nb7 bulk phases. The simple empirical model for the estimation of Ni63.5Nb36.5 cluster size was suggested, and the obtained values (7.64 A, 8.08 A) are in good agreement with STM measurements data (8 A-10 A).