Ligas multicomponentes produzidas a partir de cavacos de Ti e/ou materiais com pureza comercial para armazenagem de hidrogênio

Abstract

This work aims to investigate multicomponent alloys for hydrogen storage through the formation of metal hydrides, using titanium alloy scrap (Ti Grade 2 – ASTM F67 and Ti6Al4V-ELI – ASTM F136) and commercially pure metallic elements, with the goal of obtaining more sustainable materials in terms of the environmental impact of raw materials. Initially, the Ti-V-Nb-Cr system was studied by replacing high-purity Ti with Ti6Al4V-ELI scrap, resulting in the Ti18Nb23V24Cr33Al2 alloy, whose major phase exhibits a body-centered cubic (BCC) structure. The presence of Al and the lower Ti content increased the equilibrium pressure and reduced hydride stability compared to the reference alloy (TiVNb)65Cr35, produced from high-purity elements. Nevertheless, the recycled alloy showed a hydrogen storage capacity of 2.7 wt.% H at room temperature and improved cyclic stability. To further reduce the carbon footprint, vanadium was eliminated from the composition, as primary V presents the highest CO2-equivalent emissions in the Ti-V-Nb-Cr system. Alloys from the T-Nb-Cr system were then developed using Ti Grade 2 and Ti6Al4V-ELI scrap. The Ti33Nb33Cr33 and Ti32Al2V1Nb37Cr28 alloys exhibited predominantly BCC microstructures, with a fraction of C15Laves phase, and hydrogen storage capacities between 2.25 and 2.5 wt.% H. CO2 emissions associated with raw materials were reduced by approximately 30% after removing V from the composition. Finally, the Ti15Zr17Fe22Mn21Cr22Al2V1 alloy, produced from Ti6Al4V-ELI scrap and commercial elements, was investigated. This alloy formed a C14 Laves phase and exhibited a hydrogen storage capacity of 1.2 wt.% H, with excellent reversibility at room temperature. Despite the lower capacity, the emissions associated with its raw materials were only 1.3 kg CO2-eq, corresponding to reductions of 89% and 80% compared to the Ti-V-Nb-Cr and Ti-Nb-Cr systems, respectively.