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The research presented in this paper concerns the influence of the rate of plastic deformation generated directly in the processes of severe plastic deformations on the microstructure and properties of three metals: copper, iron and zinc. The equal channel angular pressing (ECAP) method was used, and it was performed at a low plastic deformation rate of ∼ 0.04 s−1 . The high plastic strain rate was obtained using the hydrostatic extrusion (HE) method with the deformation rate at the level of ∼ 170 s−1 . For all three tested materials different characteristic effects were demonstrated at the applied deformation rates. The smallest differences in the mechanical properties were observed in copper, despite the dynamic recrystallization processes that occurred in the HE process. In Armco iron samples, dynamic recovery processes in the range of high plastic deformation rates resulted in lower mechanical properties. The most significant effects were obtained for pure zinc, where, regardless of the method used, the microstructure was clearly transformed into bimodal after the ECAP process, and homogenized and refined after the HE process. After the HE process, the material was transformed from a brittle state to a plastic state and the highest mechanical properties were obtained. [ABSTRACT FROM AUTHOR]

To satisfy the most stringent criteria in terms of new cardiovascular stents, pure Zn was alloyed with 1 wt pct of Mg and subsequently subjected to plastic deformation, using conventional hot extrusion followed by multi-pass hydrostatic extrusion. A detailed microstructural and textural characterization of the obtained materials was conducted, and mechanical properties were assessed at each pass of deformation process. In contrast to pure Zn, hydrostatically extruded low-alloyed Zn is characterized by a remarkable increase in strength and ductility (YS = 383 MPa, E = 23 pct), exceeding the values needed for stents. Such behavior is associated with a dual microstructure containing fine-grained Zn, alternatively arranged with bands of a fragmented eutectic. Extensive grain refinement was achieved due to the process of continuous dynamic recrystallization. Hydrostatic extrusion changes the initial ⟨ 10 1 ¯ 0 ⟩ fiber texture to a 〈0002〉 and ⟨ 10 1 ¯ 1 ⟩ double fiber texture in which the 〈0002〉 component decreases with each pass of hydrostatic extrusion. The gradual evolution of texture components was simulated using a visco-plastic self-consistent model, which confirmed that, during hydrostatic extrusion, secondary slip systems were activated involving mostly the pyramidal one. [ABSTRACT FROM AUTHOR]

The paper presents the microstructural investigation of a friction-welded joint made of 316L stainless steel with an ultrafine-grained structure obtained by hydrostatic extrusion (HE). Such a plastically deformed material is characterized by a metastable state of energy equilibrium, increasing, among others, its sensitivity to high temperatures. This feature makes it difficult to weld ultra-fine-grained metals without losing their high mechanical properties. The use of high-speed friction welding and a friction time of <1 s reduced the scale of the weakening of the friction joint in relation to result obtained in conventional rotary friction welding. The study of changes in the microstructure of individual zones of the friction joint was carried out on an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) analysis system. The correlation between the microstructure and hardness of the friction joint is also presented. The heat released during the high-speed friction welding initiated the process of dynamic recrystallization (DRX) of single grains in the heat-affected zone (HAZ). The additional occurrence of strong plastic deformations (in HAZ) during flash formation and internal friction (in the friction weld and high-temperature HAZ) contributed to the formation of a highly deformed microstructure with numerous sub-grains. The zones with a microstructure other than the base material were characterized by lower hardness. Due to the complexity of the microstructure and its multifactorial impact on the properties of the friction-welded joint, strength should be the criterion for assessing the properties of the joint. [ABSTRACT FROM AUTHOR]

The study was concerned with improving the thermo-plastic treatment of the CuCrZr alloy so as to achieve a better compromise between its electrical conductivity and hardness. The experiments included severe plastic deformation (SPD), such as hydrostatic extrusion (HE), equal channel angular pressing (ECAP), and a combination of these processes, all followed by a precipitation hardening stage (solution treatment before the deformation and post-deformation ageing). The aim was to produce a material with a strongly refined microstructure (which is a factor promoting high hardness and high mechanical strength of the material) with the preservation of its high electrical conductivity. The material obtained had an ultrafinegrained structure ( d 2 = 200 nm) and a high ultimate tensile strength UTS = 630 MPa, values which are much higher than those of the reference commercial material used for the fabrication of the spot-welding electrodes. The optimization of the process parameters also permitted achieving a high electrical conductivity of 78% IACS. The CuCrZr alloy is commonly used as the material for the tips of the spot-welding electrodes, especially in the transportation industry. Therefore, the properties of the material obtained in the present study were verified from the applicative point of view i.e. some standardized spot-welding electrodes were fabricated of it and subjected to lifetime tests. The lifetime of the electrodes made of the material subjected to HE + post-deformation ageing appeared to be more than 6 times as long as that of the reference commercial electrodes. In the material treated by ECAP + HE, the result was much less advantageous which was because of the weaker morphological texture compared to that formed characteristically in the materials treated by HE alone. [ABSTRACT FROM AUTHOR]