Abstract
The influence of processing modes, swaging+drawing and rolling, on the development of nanostructures in flux melted Ag-40at%Cu alloy was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, X-ray diffraction, nano hardness testing and micro hardness testing. Microstructural evolution in the materials can be classified into two strain regimes; low strains (ε<2.5) and high strains (ε≥2.5). At low strain, the swaged+drawn material was characterized by the presence of Cu segregations and lamellar eutectic structure, which consisted of alternating Ag and Cu laminates. At high strains, ε≥2.5, the Cu segregations were homogenized and aligned in the drawing direction. Contrastingly, the rolled materials revealed eutectic structure at the early stages of rolling, suggesting that rolling homogenizes the microstructure earlier than swaging+drawing. At high strains (ε≥2.5), the rolled materials developed shear bands, and this phenomenon was not observed in, the swaged+drawn material. Upon annealing at 350oC for 1 hr in Argon, the microstructure of the swaged+drawn samples and rolled samples were similar to their respective as-deformed samples. However, silver precipitates were observed in the annealed swaged+drawn material at ε≥2.5. This phenomenon was not seen in the rolled material until ε=4.5. It is important to note that the silver precipitates were confirmed by energy dispersive X-ray spectroscopy. The texture in both the Ag and Cu phases of the swaged+drawn material showed a typical fcc fiber duplex texture. Texture evolution in both phases was similar and was a function of the deformation strain: at low strains (ε<2.5) there was some oscillation in all the components; however, at high strains (ε≥2.5) the texture components were all stable with the exception of the <111> component. The annealed texture was different from the as-deformed texture, and showed extensive perturbation of the components at high strains. The texture observed in the Ag phase of the rolled material showed that with the exception of the Shear2 {111}<110> component, there was little or no effect of strain on the evolution of texture. The deformation texture components seen in Cu phase of the rolled material were near stable with the exception of the Shear3 {112}<110> and Rotated Cube {013}<100> components, which oscillated with strain. Texture components affected upon annealing in the Ag phase included the Shear2, Brass, S and Goss components. The Shear2 and Brass components had a mutually opposite relationship, with a decrease in one being accompanied with the increase in the other. The S component decreased uniformly at all strains, while the Goss component displayed an increase in intensity at ε=4.5 coinciding with the development of Ag precipitates. The volume fraction of the Rotated Cube component was high and of the same value at all strains in the Cu phase of the annealed rolled material suggesting that the material recrystallized during heat treatment, while the S component decreased at all strains similar to the Ag phase. The nano indentation data showed that cold working the material resulted in an increase in hardness by 66%. The swaged+drawn material and the annealed swaged+drawn material showed a hardness value that increased with increasing strain up to the peak value of ε=2.5 where it remained stable until ε=3.6 and dropped thereafter. The hardness of the rolled material seemed to decrease continuously with strain, while the hardness value of the annealed rolled material coincided with the values seen in the annealed swaged+drawn material at each strain. Micro hardness testing of the swaged+drawn material showed an oscillating behavior with increasing strain, while the micro hardness testing of the rolled material was similar in trend to the nano hardness data. Upon annealing, the micro hardness values of both processing methods were relatively the same for each strain, suggesting that the micro hardness values for the annealed material was independent of the processing mode.
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