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• Ti grade 4 after 3-pass HE and RS presents strong microstructure anisotropy. • MAO coating is uniform on side walls and top surface of extruded rod. • Na 2 HPO 4 electrolyte produced coating of mixed amorphous and crystalline nature. • Large HAGB density allowed to form continuous amorphous layer close to substrate. • This layer eliminates effect of anisotropic substrate on coating microstructure. In this work, the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied. The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmission electron microscopy revealed that, by using an Na 2 HPO 4 electrolyte, a well-adherent porous coating is produced on the top surface and side walls of the extruded rod. The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy. The chemical elements dissolved in the electrolyte (Na, P and O) incorporated into the coating. Sodium locates preferentially in the outer part of the coating, while phosphorus and oxygen are distributed throughout the whole coating. The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries (HAGB), which in turn secured the formation of a continuous amorphous layer close to the substrate. The presence of this layer compensates for the effect of anisotropic substrate, producing a comparable and homogenous microstructure with a large number of micropores. [ABSTRACT FROM AUTHOR]

The study is concerned with the mechanical properties of Zn and three Zn–Mg double alloys with Mg concentrations: 0.5%, 1.0% and 1.5% in the form of rods with a diameter of 5 mm as potential materials for use in biodegradable medical implants, such as vascular stents. The materials were cast, next conventionally hot extruded at 250 °C and finally, hydrostatically extruded (HE) at ambient temperature. Occasionally HE process was carried at liquid nitrogen temperature or in combination with the ECAP process. After HE, the microstructure of the alloys was made up of fine-grained αZn of mean grain size ~1 μm in a 2-phase coat of 50–200 nm nano-grains of the fine αZn + Mg2Zn11eutectic. The 3 to 4-fold reduction of grain size as a result of HE allowed an increase in yield strength from 100% to over 200%, elongation to fracture from 100% to thirty fold and hardness over 50% compared to the best literature results for similar alloys. Exceptions accounted for elongation to fracture in case of Zn-0.5 Mg alloy and hardness in case of Zn-1.5 Mg alloy, both of which fell by 20%. For the Zn-0.5 Mg and Zn–1Mg alloys, after immersion tests, no corrosive degradation of plasticity was observed. Achieving these properties was the result of generating large plastic deformations at ambient temperature due to the application of high pressure forming with the cumulative HE method. The results showed that Zn–Mg binary alloys after HE have mechanical and corrosive characteristics, qualifying them for applications in biodegradable implants, including vascular stents.

The stored energy, present in a material after deformation in the form of dislocation density, plays a crucial role in the recrystallizaton process. It can be evaluated directly using electron diffraction or indirectly using X-ray and neutron diffraction (peak profile study). The stored energy can be also calculated, using deformation models. Knowledge of the stored energy distribution is necessary in quantitative studies of recrystallization. The distribution of stored energy can explain the highly oriented nucleation (case of most of b.c.c. metals) as well as the highly oriented growth (case of most of f.c.c metals).

The stored energy, present in a material after deformation in the form of dislocation density, plays a crucial role in the recrystallizaton process. It can be evaluated directly using electron diffraction or indirectly using X-ray and neutron diffraction (peak profile study). The stored energy can be also calculated, using deformation models. Knowledge of the stored energy distribution is necessary in quantitative studies of recrystallization. The distribution of stored energy can explain the highly oriented nucleation (case of most of b.c.c. metals) as well as the highly oriented growth (case of most of f.c.c metals).

The dependence of the flow stress on the orientation of the stress axis in the plane of textured zinc sheet has been investigated, both experimentally and theoretically. The theoretical investigation consisted of simulating the deformation process by using a generalized Taylor model (based on the minimum-work condition) and the Sachs model (based on the Schmidt shear-stress law). The deformation modes considered were slip and mechanical twinning. Only with the Taylor model was the orientation distribution consistent with the experimentally determined pole figures. The work done and the flow stress for a given plastic strain were therefore calculated for this orientation distribution using the Taylor model. The calculated and measured quantities exhibited the same directional dependence. This anisotropy can be attributed to the different activations for basal and pyramidal slip systems.MST/80

The principal KoBo device is a press with a forward-backward rotating die, enabling the extrusion of ingots under conditions of constant destabilization of their substructure. Polycrystalline grade 2 titanium was subjected to warm KoBo type extrusion. Microstructure of the material was investigated by means of Electron Backscatter Diffraction (EBSD) in the scanning electron microscope. It clearly shows deformation-induced grain fragmentation. The EBSD maps reveal heterogeneous microstructure built of ribbons curled about the extrusion direction (ED) and some equiaxed or cigar-like grains. Sizes of grains vary in the range 70 - 1500 nm for the minor axis and 350 - 20000 nm for the major axis. The material has a relatively sharp nearly axial texture with the <0001> axis perpendicular to ED. In misorientation angle distribution, besides the peak at low angle boundaries, there are three other peaks at about: 29.7deg, 89.7deg and 93.2deg. They do not correspond to any twin boundaries or low S coincidence site lattice misorientations.