Abstract
The hot deformation behavior of a harmonic-structured pure nickel has been studied and compared with the hot deformability of a homogeneously structured nickel. Both materials were produced via the powder metallurgy route through the Spark Plasma Sintering (SPS) of mechanical milled and un-milled powders. Hot deformation was evaluated through compression tests at three different temperatures (400 °C, 800 °C, and 1300 °C), covering a wide range in the homologous temperature spectrum for Ni (from 0.39 to 0.91), and at three different strain rates (0.001, 0.01, and 0.1 s−1). The evaluation of the stress–strain curves showed a higher hot compression resistance for the harmonic-structured nickel, together with higher strain hardening and strain rate sensitivity, thanks to the peculiar microstructural features of this material. Through the metallographic analysis of the specimens after hot compression, different mechanisms were identified as responsible for the deformation behavior in relation to the temperature of testing. While at 400 °C dynamic recrystallization has slightly started, at 800 °C it is widely diffused, and at 1300 °C it is replaced by grain growth and diffusion creep phenomena.
Highlights
The development of high-strength structural materials that are tough enough to resist failure has always been a challenge for materials science research
Extensive investigations in the past few decades have indicated that a reduction in grain sizes results in an increase in strength at the expense of ductility [1,2]
Harmonic structure (HS)-designed materials are newly developed hetero-structured materials that consist of a topological arrangement of coarse-grains (Core) surrounded by a three-dimensional connected network of fine grains (Shell) [8,9,10]
Summary
The development of high-strength structural materials that are tough enough to resist failure has always been a challenge for materials science research. Materials with mechanical, chemical, and microstructural intentional heterogeneities have gained huge interest owing to their potentiality in achieving a good combination of strength and ductility [3,4,5,6,7]. These purposed heterogeneities induce nonidentical plastic deformation with consistent strain gradients at the nano-scale level, thereby enhancing strain hardening. The response of these materials to high-temperature deformation has not yet been investigated and a comprehensive study on their hot deformability would be very important for the rational design of these materials, having the desired performance and properties for intended applications.
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