INFLUENCE OF Fe2+ CONCENTRATION ON THE MÖSSBAUER SPECTRA OF NixFe3-xO4 SYSTEM

On a étudié les spectres Mössbauer du système NixF3-xO4 à la température ambiante. Le champ magnétique hyperfin et le déplacement isomérique pour Fe57 en position octaédrique montrent une dépendance en fonction de la teneur en Fe2+ qui est compatible avec un comportement plutôt collectif des électrons 3 d des ions de fer pour les compositions x 0,7.The room temperature spectra of the NixFe3-xO4 system were investigated. The dependence on the Fe2+ concentration of the B site magnetic hyperfine field and of the isomer shift is a good evidence for a mostly non-localized behaviour of the iron 3 d electrons in the compositional range x 0,7

Evaluation of lubricants for electrically-assisted forming

The automobile and aerospace sectors are increasingly turning their attention to the opportunities created by the use of lightweight alloys with large strength-to-weight ratios, such as aluminium, magnesium, stainless steel, and titanium alloys. However, when using conventional forming processes, these light materials create processing challenges: low formability and high yield strength. Electrically assisted forming (EAF) is a method that can overcome these limitations. Specifically, EAF is a novel forming process where electricity is applied to the metallic workpiece during deformation. Previous investigations have shown that EAF creates a reduction in flow stress, an increase in formability, an ability to reduce/eliminate springback, and an improved precision. This study investigates the influence of electricity on lubricant performance and identifies lubricant candidates for EAF. When electricity is applied, besides the changes due to surface expansion at the interface that occur in conventional processes, the lubricant is exposed to high localized temperatures and current fields. Electrically assisted ring compression tests are conducted and the performance characteristics of three lubricants are evaluated. By combining the experiments and finite element simulation results, friction coefficients can be estimated, and the effect of electric current flow on friction characteristics quantified