Deformation mechanisms and properties of nanocrystalline Al, Ni and Al80Ti15Ni5 alloy: a molecular dynamics study

• Ano de defesa: 2021
• Autor(a) principal: Barboza, Alexandre Melhorance
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade do Estado do Rio de Janeiro; Centro de Tecnologia e Ciências::Instituto Politécnico; Brasil; UERJ; Programa de Pós-Graduação em Modelagem Computacional
• Palavras-chave em Português: Nanocrystalline materials; Aluminum; Nickel; Titanium; Molecular dynamics; Hall-Petch; Deformation mechanisms; Metais; Propriedades mecânicas; Deformação; Dinâmica molecular; Métodos de simulação; Materiais nanocristalinos; Alumínio; Níquel; Titânio; Mecanismos de deformação; CIENCIAS EXATAS E DA TERRA
• Link de acesso: http://www.bdtd.uerj.br/handle/1/16797

Nanocrystalline metals and alloys show promising properties for technological applications. However, their unusual mechanical behavior proved to be a real challenge to be understood. Experimental studies of these materials are affected by complexity and cost in creating a bulk sample free of defects. Thus, molecular dynamics simulations have emerged as an important tool to assess, at atomic level, the phenomena responsible for their behavior. In this thesis, three different nanocrystalline systems (Al80Ti15Ni5 alloy, pure nickel, and pure aluminum) were studied using molecular dynamics. The focus was to analyze the systems´ mechanical behavior with special attention to the inverse Hall-Petch relationship and the related deformation mechanisms. Atomic arrangement analysis of the ternary alloy demonstrated the grain boundary sliding and diffusion as the dominant deformation mechanisms. In addition, deformation mechanisms present in amorphous materials seems to be capable of work in nanocrystalline systems. The results related to nanocrystalline nickel demonstrated that partials dislocation remain active regardless of grain size. However, other deformation mechanisms, such as grain rotation and grain boundary sliding, takes place below a critical grain size of circa 20 nm, leading to the inverse Hall-Petch relationship. Moreover, a distinct strain rate sensitivity behavior was found, in which it decreases with the grain size reduction. Regarding the nanocrystalline aluminum, Coble creep phenomenon was observed and no clearly indication of dislocation pile-up was evidenced.