Estudo do efeito da adição de pentóxido de nióbio na microestrutura e propriedades do aço Eurofer processado pela metalurgia do pó

• Ano de defesa: 2022
• Autor(a) principal: Menezes, Roberta Araújo Cavalcante de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Rio Grande do Norte; Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM CIÊNCIA E ENGENHARIA DE MATERIAIS
• Palavras-chave em Português: Eurofer; Nb2O5; Metalurgia do pó; Moagem de alta energia; Sinterização; CNPQ::ENGENHARIAS::ENGENHARIA DE MATERIAIS E METALURGICA
• Link de acesso: https://repositorio.ufrn.br/handle/123456789/56512

EUROFER is the reference steel for manufacturing structural components used in nuclear fusion reactors. It is a reduced activity ferritic-martensitic (RAFM) stainless steel, with has its good mechanical strength, corrosion resistance, creep resistance, and reduced radioactive activity, as well as a low ductile-to-brittle transition temperature. However, being a stainless steel, it cannot operate at temperatures exceeding 500 °C, as microstructural changes occur, leading to material embrittlement. Studies have been conducted to mitigate this issue, and the solution was to strengthen the steel through oxide dispersion strengthening (ODS) with yttrium oxide processed via powder metallurgy (PM). The objective of this work is to contribute to the development of new EUROFERbased alloys with the addition of niobium pentoxide (Nb2O5) processed by PM using highenergy milling (HEM) and sintering via Spark Plasma Sintering (SPS). Pure EUROFER chips were milled in a high-energy ball mill for different times (5h, 10h, and 15h), both with and without the addition of Nb2O5 (0%wt., 3%wt., 5%wt., and 7%wt.) over the same time intervals. The powders were sintered via SPS and conventional furnace (CF). The effects of milling time and Nb2O5 concentration, as well as sintering methods, on the physical, mechanical, and magnetic properties of the sintered materials were analyzed. The results showed that increasing the milling time reduced the average particle size distribution by 57% and improved the sinterability of the milled powders. X-ray diffraction (XRD) and magnetic analyses of the powders with added Nb2O5 suggest a new composition of the steel's solid solution. XRD analyses of SPS-sintered samples reveal the formation of retained martensitic and austenitic phases. The microhardness of the alloys obtained from pure EUROFER chips sintered by SPS (≈ 560 HV) was higher than those sintered by CF (≈ 65 HV) and the as-received bar (410 HV). The addition of Nb2O5 to the steel maintained the microhardness of samples sintered via SPS in the same order of magnitude as the bar, while those sintered via CF exhibited lower values (≈ 78 HV). Furthermore, the densities of the samples sintered via SPS were higher than those sintered via CF. Given the presented results, the production of these new alloys holds promise for developing new materials with lower density and higher hardness compared to the initial EUROFER alloy.