Search

In this study, the Zn-0.8Mg-0.28CaO wt.% composite was successfully prepared using different conditions of ball milling (rotations and time) followed by a direct extrusion process. These materials were characterized from the point of view of microstructure and compressive properties, and the correlation between those characteristics was found. Microstructures of individual materials possessed differences in grain size, where the grain size decreased with the intensified conditions (milling speed and time). However, the mutual relation between grain size and compressive strength was not linear. This was caused by the effect of other factors, such as texture, intermetallic phases, and pores. Material texture affects the mechanical properties by a different activity ratio between basal and pyramidal slips. The properties of intermetallic particles and pores were determined in material volume using micro-computed tomography (µCT), enhancing the precision of our assumptions compared with commonly applied methods. Based on that, and the analysis after the compressive tests, we were able to determine the influence of aspect ratio, feret diameters, and volume content of intermetallic phases and pores on mechanical behavior. The influence of the aspects on mechanical behavior is described and discussed. [ABSTRACT FROM AUTHOR]

Recently, the complex shearing of extruded tube (CSET) technique was proposed representing a new way of processing tubes from a bulk billet as a combination of extrusion with two passes of equal channel angular processing and possible mandrel rotation. In the present paper, the influence of mandrel rotation on the final microstructure and mechanical properties of the tube fabricated of a 3003 aluminium alloy was investigated. Electron back scatter diffraction (EBSD) revealed differences in grain size and misorientation angles between tubes processed with stationary and rotating mandrel. Kernel average misorientation maps obtained from EBSD experiments and ASTAR analysis performed in transmission electron microscopy proved differences in the dislocation density and arrangement. The tube processed using a stationary mandrel showed a recovered microstructure with elongated grains separated by low-angle grain boundaries into subgrains. The microstructure of the tube processed with a rotating mandrel was dynamically recrystallized with the grain size in submicrometer range. Vickers microhardness measurements revealed only a 40% HV increase in the sample prepared using stationary mandrel as compared with the initial billet. The mandrel rotation resulted in a much higher HV increase up to 200% as a result of substantial grain refinement. [ABSTRACT FROM AUTHOR]

The increasing incidence of trauma in medicine brings with it new demands on the materials used for the surgical treatment of bone fractures. Titanium, its alloys, and steel are used worldwide in the treatment of skeletal injuries. These metallic materials, although inert, are often removed after the injured bone has healed. The second-stage procedure—the removal of the plates and screws—can overwhelm patients and overload healthcare systems. The development of suitable absorbable metallic materials would help us to overcome these issues. In this experimental study, we analyzed an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. From this alloy we developed screws which were implanted into the rabbit tibia. After 120, 240, and 360 days, we tested the toxicity at the site of implantation and also within the vital organs: the liver, kidneys, and brain. The results were compared with a control group, implanted with a Ti-based screw and sacrificed after 360 days. The samples were analyzed using X-ray, micro-CT, and a scanning electron microscope. Chemical analysis revealed only small concentrations of zinc, strontium, and magnesium in the liver, kidneys, and brain. Histologically, the alloy was verified to possess very good biocompatibility after 360 days, without any signs of toxicity at the site of implantation. We did not observe raised levels of Sr, Zn, or Mg in any of the vital organs when compared with the Ti group at 360 days. The material was found to slowly degrade in vivo, forming solid corrosion products on its surface. [ABSTRACT FROM AUTHOR]

There is currently an increasing demand for metals with a hexagonal close-packed structure (HCP). Particularly, titanium and its alloys are widely used in aerospace, aircraft and the medical industry [[1]]; zirconium is used in the nuclear industry [[1]] and Mg-based alloys in the automotive and aircraft industry [[1]]. Fojt et al. [[12]] dealt with the corrosion behavior of a SLM-processed Ti alloy. From the aforementioned, it is clear that the mechanical behavior of metals and alloys with a HCP structure is very sensitive to the microstructure and texture of the material. [Extracted from the article]

A new severe plastic deformation technique, known as the complex shearing of extruded tube (CSET), was applied to a 3003 based model aluminium alloy. This technique, consisting of a combination of extrusion and two consecutive Equal Chanel Angular Pressing (ECAP) passes accompanied with concurrent torsional straining, is capable to produce a fine-grained tubular sample directly from a bulk metallic cylinder in one forming operation. In the present paper, the microstructural development of the alloy during partial processes of CSET was studied in detail using light microscopy, electron backscatter diffraction, and transmission electron microscopy. It was found that CSET technique refines the grain size down to 0.4 µm and, consequently, increases the microhardness from the initial value of 40 HV to the final value of 120 HV. The contributions of partial processes of CSET to the total strain were estimated. [ABSTRACT FROM AUTHOR]

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn–0.8Mg–0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated. [ABSTRACT FROM AUTHOR]

In this study, we prepared zinc wires with a diameter of 250 µm by direct extrusion using an extrusion ratio of 576. We studied the influence of the extrusion temperature and microstructure of the initial Zn billets on the microstructural and mechanical characteristics of the extruded wires. The extrusion temperature played a significant role in the final grain size. The wires extruded at 300 °C possessed a coarse-grained microstructure and the shape of their tensile stress–strain curves suggested that twinning played an important role during their deformation. A significant influence of the initial grain size on the final microstructure was observed after the extrusion at 100 °C. The wires prepared from the billet with a very coarse-grained microstructure possessed a bimodal grain size. A significant coarsening of their microstructure was observed after the tensile test. The wires prepared from the medium-grained billets at 100 °C were relatively coarse-grained, but their grain size was stable during the straining, resulting in the highest ultimate tensile strength. This preliminary study shows that strong attention should be paid to the extrusion parameters and the microstructure of the initial billets, because they significantly influence the microstructure and mechanical behavior of the obtained wires. [ABSTRACT FROM AUTHOR]

Zinc and its alloys seem to be promising candidates for biodegradable applications. Those materials are often modified by other elements or compounds in order to enhance their properties. The combination of zinc and apatites is challenging for several reasons. However, the advantages connected with the biological aspects suggest the need for further research into such materials. In this study, three zinc-based composites with 4 and 8 wt. % of nanohydroxyapatite or nanomonetite (Zn-4MO, Zn-4HA, Zn-8HA) were prepared by sintering and subsequent extrusion. Materials prepared in this way were characterized from the microstructural, mechanical and corrosion point of view. The obtained results showed a significant influence of particle character (amount and morphology) on the strength and ductility of the prepared materials. In case of Zn-4MO, the presence of monetite significantly increased the ductility compared with the other materials. In addition, the increment of the degradation rate caused by the presence of monetite was observed as well. All obtained results pointed out to significant advantages of monetite for the preparation of Zn-apatite composites compared with hydroxyapatite. [ABSTRACT FROM AUTHOR]

Zinc and its alloys belong to a group of biodegradable materials, which can be potentially used for the preparation of temporary orthopedic implants. The research of biodegradable zinc materials revealed a lot of limitations; however, the new processing approaches of those materials can enhance their properties, which are insufficient for now. In this study, the zinc composite with 8 wt.% of hydroxyapatite (Zn/HA8) prepared for the first time by extrusion process was characterized from the point of view of the structural, mechanical and corrosion properties. The extrusion process led to good integrity of the interfaces between the zinc and hydroxyapatite particles. Mechanical behavior confirmed the role of hydroxyapatite as a defect in the material structure, which led to a decrease of the Zn/HA8 mechanical properties by approximately 30% (compressive yield strength (CYS) = 154 MPa Zn, 113 MPa Zn/HA8). Despite that, the Zn/HA8 composite showed sufficient mechanical properties for cancellous bone replacement and reached the lower limit for cortical bone. Additionally, the presence of hydroxyapatite caused the preferential precipitation of hydroxyapatite (HA) from the solution and can lead to a significant enhancement of the tissue/implant interface interactions. [ABSTRACT FROM AUTHOR]

Zinc and zinc alloys have been studied due to their corrosion properties as potentially biodegradable materials. In this study, a zinc/hydroxyapatite composite (Zn/HA) containing 16 wt % HA was prepared by spark plasma sintering and characterized in detail. The microstructure, mechanical and corrosion properties were studied and the mutual relations between properties and microstructure were found. The porosity was evaluated to be approximately 18%. The mechanical properties (ultimate compression strength = 65 MPa and ultimate flexural strength = 120 MPa) are sufficient for the potential scaffolding and augmentation of cancellous bone. The flexural properties of these materials were measured for the first time. Immersion tests and subsequent analyses confirmed no direct participation of hydroxyapatite in the corrosion process and an ideal corrosion rate of approximately 0.4 mm/year. The amount of released zinc was between 4–6 mg/day corresponding with the maximal usable surface area of 25 cm2. All the results suggest that the Zn/HA composite is suitable as a potential biodegradable material (from the point of view of mechanical and corrosion properties) for the replacement of cancellous bones. [ABSTRACT FROM AUTHOR]

Zinc-based alloys represent one of the most highly developed areas regarding biodegradable materials. Despite this, some general deficiencies such as cytotoxicity and poor mechanical properties (especially elongation), are not properly solved. In this work, a Zn-5Mg (5 wt.% Mg) composite material with tailored mechanical and superior corrosion properties is prepared by powder metallurgy techniques. Pure Zn and Mg are mixed and subsequently compacted by extrusion at 200 °C and an extrusion ratio of 10. The final product possesses appropriate mechanical properties (tensile yield strength = 148 MPa, ultimate tensile strength = 183 MPa, and elongation = 16%) and decreased by four times the release of Zn in the initial stage of degradation compared to pure Zn, which can highly decrease cytotoxicity effects and therefore positively affect the initial stage of the healing process. [ABSTRACT FROM AUTHOR]