Resumo:
High-Entropy Alloys (HEAs) have emerged as promising candidates for solid-state
hydrogen storage in the form of metal hydrides, particularly those with a body-centered
cubic (BCC) structure, due to their high density of interstitial sites, thermal stability,
and compositional flexibility. Although alloys from the TiVNbCrMn system processed
by arc melting have shown promising results in the literature, the limitations of this
method, such as phase segregation, material loss, and large differences in melting
points, justify the evaluation of high-energy ball milling (HEBM) as an alternative route.
In this context, this work investigated the processing of the HEAs Ti32V32Nb18Cr9Mn9
(HEA A) and Ti27.5V27.5Nb20Cr12.5Mn12.5 (HEA B). The processing was carried out in
a planetary ball mill at 350 rpm, with a ball-to-powder ratio (BPR) of 10:1, under argon
atmosphere, using 15 g of elemental powders per vial, with samples collected
at 10-hour intervals up to a total milling time of 40 hours. After milling, the powders
from the final samples were compacted and subjected to heat treatment at 450 °C for
1 hour. The samples were then characterized by X-ray diffraction (XRD), scanning
electron microscopy (SEM), energy-dispersive spectroscopy (EDS), thermal analysis
(DSC), particle size distribution, and hydrogen absorption/desorption tests to evaluate
their hydrogen storage properties. The results showed that both alloys exhibited increasingly
homogeneous microstructures and refined particles with longer milling times.
XRD analyses confirmed the presence of two BCC phases both before and after the
heat treatment of the 40-hour milled samples, which remained stable up to 1000 °C.
Regarding hydrogenation properties, HEA A exhibited a maximum hydrogen absorption
of 1.4 wt.%, outperforming HEA B (0.5 wt.%), with both alloys showing nearly
instantaneous absorption, indicating rapid kinetics promoted by HEBM. These findings
demonstrate that HEBM is a promising route for the development of HEAs for hydrogen
storage applications, offering advantages such as high surface area and enhanced
absorption kinetics.
