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Javed S. Ibrahim ,Rohit T. Mathew,M. J. N. V. Prasad,K. Narasimhan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.10
Owing to high heat flux ability and good mechanical strength, copper has been used for micro-electro-mechanical systems(MEMS) components with dimensions in micrometers processed by electrochemical methods. In the present study, finegrained copper foils of different thicknesses and grain sizes produced by pulsed electrodeposition under different controlledcurrent densities were used to investigate the effect of total number of grains across thickness of foil on its tensile responseand formability. For a comparative study, commercially available rolled Cu foils were also used. Vacuum annealing wasemployed to obtain a wide range of fully recrystallized grain sizes within same thickness of the foils. Detailed microstructuralcharacterization was carried out using scanning electron microscope attached with electron backscattered diffraction detector. The foils were subjected to uniaxial tensile testing and formability testing using a miniaturized Nakazima test setup. Asanticipated, finer the grain size higher was the yield strength. However, the strength of copper reduced with decreasing thetotal number of grains across thickness of the foil. The electrodeposited Cu foil exhibited relatively higher strength levelsbut reduced tensile ductility along with decreased strain hardening ability compared to the fully recrystallized Cu foils havingsimilar grain sizes. Furthermore, the number of grains across thickness and the prior history of foils played significantrole on the shape and trend in variation of the forming limit curve of Cu. An α-fiber (< 110 >) texture evolved in Cu duringdeformation and its volume fraction strengthened under biaxial deformation conditions.
Javed S. Ibrahim,M. J. N. V. Prasad,Partha Sarkar,K. Narasimhan 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.2
Ultra-low carbon (ULC) steels, containing a carbon content ~ 0.055 wt%, have been used in several applications in the formof thin foils. However, there are limited studies on the effects of foil thickness (t) to grain size (d) ratio and foil condition onthe tensile response and formability of thin ULC steel foils. In the present work, the tensile and forming behaviours of ULCsteel foils of thickness about 400 μm were evaluated in both annealed and prestrained (by cold reduction to 2–7%) conditionsas a function of t/d ratio and followed by detailed texture evolution analysis. Vacuum annealing was used to achievevarying t/d ratios in the specimens. Additionally, thin ULC steel foils of 100 μm thickness in annealed condition were alsoused for examining the thickness effect. Microstructural analysis was performed using the electron backscattered diffractiontechnique. Microformability was assessed by a miniaturised Nakazima test setup with specimen geometries designed toproduce three different strain paths. The annealed foils displayed a typical yield-point phenomenon, but the total yield-pointelongation decreased with decreasing thickness and grain size. The foils exhibited typical Hall–Petch strengthening, coldwork hardening, and forming limit curves; however, there were substantial reductions in both tensile strength and ductility,and consequently, the forming strains, with decreasing the t/d ratio. The tensile response and formability of the foils wereadversely affected by both thinning and prestraining. The texture studies revealed the formation of a γ-fibre i.e., < 111 >||normaldirection, and its intensity varied significantly with the t/d ratio and mode of strain path.