Investigação sobre métodos de rejuvenescimento de ligas metálicas amorfas e comparação de sua eficácia na liga Zr55Cu30Al10Ni5

Abstract

Amorphous metallic alloys are alloys that have disordered atomic structure, whose atoms occupy random positions in contrast with crystalline metals, whose structure possesses translational symmetry, meaning their atoms are arranged in a regular and periodic manner. Even though this type of material has interesting properties, like high values of hardness and yield strength, good resistance to abrasion and corrosion, among others, their applications in engineering are limited because of their intrinsic fragility due to their limited plasticity, caused by a highly localized deformation behavior. In this sense, the better understanding of rejuvenation techniques is highly relevant, since they are able to enhance the plasticity of these materials and, consequently, their scope of applications. From these assumptions, it is proposed as the objective of the present work the study of selected rejuvenation techniques for amorphous metallic alloys and the comparison of the results found for their application on the Zr55Cu30Al10Ni5 alloy. For that purpose, an initial introduction on the theoretical basis about amorphous metallic alloys is made and it was defined what is rejuvenation and what are the indicators of its success. That being done, it was defined, based on their relevance and up-to-dateness, five rejuvenation methods to talk about: (i) elastostatic loading, (ii) high-pressure torsion, (iii) cryogenic thermal cycling, (iv) ionic irradiation and (v) the combination of method, more specifically, elastostatic loading with cryogenic thermal cycling. The execution of these techniques and their success in rejuvenation amorphous metallic alloys were demonstrated. A comparative analysis of these methods when applied to the Zr55Cu30Al10Ni5 alloy was done, and results were then organized on a table that demonstrates the percentual variation of relaxation enthalpy (ΔHrel), Young’s modulus (E), hardness (H) and compressive strain (ε) in regard to each rejuvenation method applied to the selected alloy. It was concluded that all techniques were able to rejuvenate the selected alloy, that high-pressure torsion had the best percentual results of all mechanical techniques, that ionic irradiation had interesting results but that its a practical use is limited beyond the laboratory and that the combination of elastostatic loading with cryogenic thermal cycling is the most promising one both in terms of results and practicality.