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The present work aims at the preparation and characterization of ceramic layered composite prepared from fine submicron-sized Al2O3 with the addition of electrospun graphene-coated Al2O3 fibers (Al2O3/G-Fs) by Spark Plasma Sintering with double pressure sintering process. A layered composite containing 2.5 wt. % of Al2O3/G fibers in three homogeneous layers was prepared and compared with the pure monolithic Al2O3 material obtained under the same conditions. The microstructures of the samples were studied by optical microscopy, scanning, and transmission electron microscopy. The presence of graphene after the sintering in the final composite was proved by Raman spectroscopy. The effect of the graphene-coated fibers on the composite`s microstructure and mechanical properties was described along with the fractographic analysis. Graphene on the surface of the electrospun Al2O3 fibers suppressed the grain growth which dominantly takes place during the sintering of the composite, which significantly influenced the character of the fracture. While predominantly intergranular fracture occurs in the monolithic fracture surface, the fracture character becomes transgranular with the addition of layers of Al2O3/G-Fs. Fracture toughness improvement took place because of the presence of small pores, in order of a few nanometers, which showed high energy absorption and provided self-induced crack propagation inhibition.

The influence of the processing route on the microstructure characteristics and mechanical properties of high-entropy carbides was investigated. The experimental materials were prepared by a combination of ball milling and spark plasma sintering at the temperature of 2100 °C. The effect of sintering time (5 min, 10 min, and 20 min) on the microstructure development and properties of the investigated systems has been studied. The microstructure analysis was performed using scanning electron microscopy + EDAX analysis on the polished surfaces. Nanoindentation was used for the nano-hardness and Young’s modulus measurements. Micro-hardness was measured using Vickers method and indentation method using a Vickers indenter was used to determine the indentation fracture resistance – fracture toughness. The measured grain size values were in the range from 5 µm to 14 µm. The nano-hardness values changed from 36 GPa to 39 GPa and the indentation modulus of elasticity from 558 GPa to 577 GPa, respectively. The measured micro-hardness values were in the range from 18.93 GPa to 21.95 GPa and the indentation fracture resistance changed from 2.70 MPa.m1/2 to 3.50 MPa.m1/2, respectively.

Zn-Fe alloys have been extensively investigated in this study with a view to their application as biodegradable bone implants. Biogenic element zinc is a very appropriate metal because of the ideal degradation rate compared to those of Mg and Fe. Studied alloys were made by compressing metallic powders in a content ratio of 100% Zn, Zn-1% Fe, Zn-2% Fe, Zn-5% Fe and Zn-10% Fe and sintering at 350 ​°C for 1 ​h. Prepared samples were examined by optical microscopy, SEM and XRD. Corrosion behavior, mechanical testing and hemocompatibility were observed subsequently. The electrochemical performance of such materials was studied in the simulated body fluids. The enhanced corrosion rate was observed for all samples after iron addition due to the micro-galvanic effect between the pure Zn and Zn11Fe intermetallic phase. The corrosion rate of the Zn-5% Fe alloyed sample was more than 20-times higher (2.89 mmpy) compared to the pure Zn. However, alloying with more than 5 ​wt % of iron diminished the mechanical performance of the material. Therefore, the performed mechanical and hemocompatibility tests showed acceptable biocompatibility of zinc and Zn-1% Fe and Zn-2% Fe samples.

Conductive Al2O3/graphene composites were manufactured by SPS from Al2O3 powders coated with a few graphene layers. Composite powders with a total carbon content of 0.1, 0.6 and 1.0 wt. % were manufactured by chemical vapour deposition. The effect of the graphene content on the microstructure, mechanical and electrical properties of the compacts were studied. Graphene, homogenously located along the grain boundaries, dramatically hindered the Al2O3 grain growth. The continuous interconnected graphene network enhanced electrical properties, achieving percolation threshold as low as 0.6 wt. % of graphene. The content of 1 wt. % of graphene increased electroconductivity by 13 orders of magnitude as compared to the monolithic alumina. The indentation fracture toughness increased by 20 % in specimens with 0.6 wt. % graphene content as compared to pure alumina. The presence of 1.0 wt. % of graphene resulted in a slight decrease of elastic modulus and hardness, but strength decreased by 40 %.

The aim of the present contribution is the processing and characterization of fiber-reinforced and layered alumina - graphene composites, prepared by the combination of electrospinning, calcination, chemical vapor deposition (CVD) and spark plasma sintering (SPS). The fiber-reinforced composite contains homogenously distributed graphene-coated polycrystalline alumina microfibers in the Al2O3 matrix. The layered composites contain Al2O3 layers and layers of graphene-coated alumina microfibers or layers of graphene-coated alumina grains of submicron size. The systems with high density, 99.5–99.9 %, show different grain sizes of Al2O3 in their constituents, changing from 0.08 to 1.9 μm in comparison to the monolithic alumina with the average grain size of 2.6 μm. The composites and their layers show increased electrical conductivity, hardness, and fracture toughness by approximately five orders of magnitude, 31 %, and 8%, respectively, in comparison to the monolithic alumina due to the presence of graphene layers, small grain-sized alumina, and microfibers in the composites.

The current trend in development of new metallic materials for certain types of implants is turning away from permanent, biologically inert materials to the use of biodegradable materials. Fe–Mn alloys represent high perspective material for development of new generation of temporary and biodegradable implants. The aim of this work was to study mechanical and corrosion characteristics of powder samples containing 25, 30 and 35 wt % of Mn which are fabricated by pressing, sintering, and additional spark plasma sintering. The influence of preparation method (pressing and sintering) to microstructure, phased composition and corrosion behavior of prepared alloys was studied.

Coating of the biodegradable metals represents an effective way of modification of their properties. Insufficient biological, mechanical, or degradation performance of pure metals may be enhanced when the proper type of organic polymer coating is used. In our previous work, the significant effect of the polyethyleneimine (PEI) coating not only on the rate but also on the type of corrosion was discovered. To bring a comprehensive overview of the Fe-PEI system performance, iron-based biodegradable scaffolds with polyethyleneimine coating were studied and their cytocompatibility and hemocompatibility, and mechanical properties were evaluated and discussed in this work. Electrochemical impedance spectroscopy (EIS) measurements were conducted for further study of material behavior. Biological analyses (MTS assay, fluorescent imaging, hemocompatibility tests) showed better cell proliferation on the surface of Fe-PEI samples but not sufficient overall cytocompatibility. Good anti-platelet adhesion properties but higher hemolysis when compared to the pure iron was also observed for the coated samples. Mechanical properties of the prepared Fe-PEI material were enhanced after coating. These findings suggest that the Fe-PEI may be an interesting potential biomaterial after further composition optimization resulting in lower cytotoxicity and better hemocompatibility.

Biodegradable metallic implants are materials that serve as a temporary implants and scaffolds. They degrade directly in vivo and therefore eliminate need for secondary surgical intervention. They are often made of metals such as magnesium, iron, zinc and can be modified by coating with the inorganic or polymeric layer. In this work iron-based biomaterial was prepared and modified with polymeric (polyethyleneimine, PEI) layer. Its degradation behavior was studied under conditions of simulated body fluids at 37 ± 0.2 °C in the form of static immersion tests. It has been shown that the surface modification caused an acceleration of degradation of the material and also had an influence on the corrosion mechanism.

Biodegradable materials have attracted a great attention in material engineering and medical community in the last decade. In certain cases, degradable implants may overcome the disadvantages of permanent devices. Any biodegradable material for medical use should support the healing process of a diseased tissue or organ and after that degrade slowly in the human body. In orthopaedic applications, biodegradable implants should allow a gradual load transfer to the healing bone as the materials degrade. Iron and iron based alloys have been identified as appropriate materials for the temporary replacement of bones, since they combine high strength at medium corrosion rates. The main goal of this work is evaluation of the in vitro biocompatibility of open cell iron foams with polyethylene glycol (PEG) coating layer for bone repair applications. Based on results of in vitro cytotoxicity studies it was found that the coating of sintered cellular iron samples with PEG layer led to a desired improvement of biocompatibility.

The wear resistance and tribological characteristics of alumina/graphene layered and fiber-reinforced composites were investigated under dry sliding conditions at applied loads of 10 N and 50 N in the air. The experimental materials were prepared by a combination of electrospinning-calcination-chemical vapor deposition and spark plasma sintering. Graphene-coated Al2O3 microfibers were used to form layers in layered monolithic alumina/graphene-coated Al2O3 microfibers composite, and as reinforcements for the alumina matrix in the fiber-reinforced composite. The microstructure, deformation, and damage characteristics were studied. Both composites show a lower coefficient of friction in comparison to alumina with the lowest value of 0.42 for the fiber-reinforced composite measured at a load of 10 N. At the load of 10 N the composites exhibit very high wear resistance with values of wear rate 2.78 × 10−8mm3/(N·m) for the layered and 1.74 × 10−8mm3/(N·m) for the fiber-reinforced composite, in comparison to the wear rate of Al2O3 with a value of 5.35 × 10−6mm3/(N·m). The significant improvement in the wear resistance of the composites was associated with the improved mechanical properties and formation of a protective tribofilm on the wear tracks by the multilayered graphene present on the surface of Al2O3 microfibers and alumina debris, which provided the lubricating effect for the composites.

Research in the field of biodegradable metallic scaffolds has advanced during the last decades. Resorbable implants based on iron have become an attractive alternative to the temporary devices made of inert metals. Overcoming an insufficient corrosion rate of pure iron, though, still remains a problem. In our work, we have prepared iron foams and coated them with three different concentrations of polyethyleneimine (PEI) to increase their corrosion rates. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used for characterization of the polymer coating. The corrosion behavior of the powder-metallurgically prepared samples was evaluated electrochemically using an anodic polarization method. A 12 weeks long in vitro degradation study in Hanks&rsquo, solution at 37 &deg, C was also performed. Surface morphology, corrosion behavior, and degradation rates of the open-cell foams were studied and discussed. The use of PEI coating led to an increase in the corrosion rates of the cellular material. The sample with the highest concentration of PEI film showed the most rapid corrosion in the environment of simulated body fluids.

At present biodegradable implants received increased attention due to their use in various fields of medicine. This work is dedicated to testing of biodegradable materials which could be used as bone implants. The samples were prepared from the carbonyl iron powder by replication method and surface polymer film was produced through sol-gel process. Corrosion testing was carried out under static conditions during 12 weeks in Hank’s solution. The quantity of corrosion products increased with prolonging time of static test as it can be concluded from the results of EDX analysis. The degradation of open cell materials with polyethylene glycol coating layer was faster compared to uncoated Fe sample. Also the mass losses were higher for samples with PEG coating. The polymer coating brought about the desired increase in degradation rate of porous iron material.

Fe-Mn alloys represent promising degradable biomaterials for temporary implants. To investigate the effect of corrosion on their mechanical properties, iron powders were mixed with 25, 30 and 35 wt.% of a manganese powder, compressed into prismatic bars and sintered. Sintered bars were immersed in Hank's solution for 8 weeks. The bending stiffness of each bar before and after its exposure to electrolyte was examined. The higher the porosity of a bar was, the higher relative reduction in bending stiffness the bar exhibited. A likely explanation was that in a more porous bar Hank’s solution penetrated deeper and affected larger volume fraction of bar’s material.

Advances in biomedicine and development of modern technologies in the last century have fostered the improvement in human longevity and well-being. This progress simultaneously initiated the need for novel biomaterials. Recently, degradable metallic biomaterials have attracted serious attention in scientific and clinical research owing to their utilization in some specific applications. This work investigates the effect of the polyethylene glycol (PEG) coating of open-cell iron and phosphorus/iron foams on their microstructure and corrosion properties. The addition of phosphorus causes a slight increase in pore size and the deposition of a polymer coating results in a smoothened surface and a moderate decrease in pore diameter. The PEG coating leads to an increase in corrosion rates in both foams and potentially a more desirable product.

Bioresorbable biomaterials are expected to degrade or to be resorbed within the body at an appropriate degradation rate rather than removing the implant after fulfilling its function. Adsorption of proteins on the metal surface and its subsequent detachment can affect the degradation mechanism and induce health complications. The iron samples were produced from carbonyl iron powder by powder metallurgy and coated by thin layer of polyethyleneimine (PEI). The effect of both PEI coating and bovine serum albumin (BSA) interaction on corrosion resistance of iron biomaterials in Hanks’ solution was investigated. Adsorption of BSA onto Fe + PEI was more rapid in comparison to adsorption onto bare Fe due to the electrostatic nature of BSA adsorption to polymeric layer. The corrosion behavior of sintered samples in Hanks’ solution without and with protein was investigated. Alteration of degradation mechanism was observed in the presence of PEI and/or BSA. PEI was observed to avoid the pitting corrosion while presence of BSA resulted in surface-induced complexation. The extensive pitting with high extent of metal release was observed in the presence of PEI and BSA. The additional spectroscopic and microscopic methods were used to prove the suggested alteration of corrosion mechanism.

The increasing demand for improved implant biomaterials encourages their design and development. Degradable biomaterials have gained considerable attention especially in the past few decades. Metallic biomaterials are commonly applied in current medical practice to replace or repair diseased tissue. Structural materials with appropriate mechanical properties are required for load-bearing orthopedic applications. Moreover, biomaterials must fulfil the safety requirements and exhibit reasonable degradation rates to support the failing tissue and allow a gradual load transfer to the healing bone. Metal foams with open cell structure allow the transport of body fluids, growth of new tissues, improvement of degradation rate and reduction of the stress shielding phenomenon. In this work, iron open cell foams were fabricated by means of powder metallurgy processes. The hemocompatibility and mechanical properties of the porous iron materials without and with polyethylene glycol (PEG) coating were evaluated depending on the time of immersion in a simulated body fluid. It has been discovered, that PEG layer has increased the density and strength of iron foams. A mechanism of corrosion of iron foams with PEG coating layer was proposed. The suppression of hemolysis extension, platelet adhesion, and thrombus formation due to the polymer layer was observed as a result.

Iron-based substrates with polyethylene glycol coating were prepared as possible materials for biodegradable orthopedic implants. Biodegradable materials that provide mechanical support of the diseased tissue at the time of implanting and then disappear gradually during the healing process are sometimes favored instead of permanent implants. The implant degradation rate should match the time of the tissue regrowth. In this work, the degradation behavior of iron-based foams was studied electrochemically during immersion tests in Hanks&rsquo, solution. The corrosion rate of the polyethylene glycol-coated samples increased and the corrosion potential shifted to more negative values. This indicates an enhanced degradation rate as compared to the uncoated material, fulfilling the goal of being able to tune the degradation rate. It is the interfacial interaction between the hydrophilic polymer layer and the iron surface that is responsible for the enhanced oxidation rate of iron.

Biodegradable metallic implants are of significant importance in the replacement of bones or the repair of bone defects. Iron-phosphate-coated carbonyl iron powder (Fe/P) was prepared by the phosphating method. Moreover, Fe/P–Mn alloy was produced by sintering the Fe/P powder mixed with manganese powder. Bare carbonyl iron samples and the Fe/P and Fe/P–Mn sintered samples were evaluated for their microstructure, cytotoxicity, and hemocompatibility. The microstructure of the sintered samples was examined using an optical microscope and scanning electron microscopic analysis. Corrosion behavior was evaluated by potentiodynamic polarization in Hank’s solution. The in vitro biocompatibilities were investigated by cytotoxicity and hemolysis tests. The results obtained demonstrate that the addition of Mn resulted in higher surface inhomogeneity, porosity and roughness as well as in increased cytotoxicity. The phosphate coating has a moderately negative effect on the cytotoxicity. The corrosion rates determined from Tafel diagrams were ordered in the following sequence: Fe/P–Mn, Fe, Fe/P from high to low. The hemocompatibility of experimental samples was ordered in the following sequence: Fe/P, Fe/P–Mn, Fe from high to low. All samples were found to be hemocompatible.

Powders comprised of Fe particles and 25, 30, 35wt.% of Mn particles were mixed, compacted and sintered to investigate the effect of Mn on the properties of sintered Fe-Mn alloys. It was found that the sample’s swelling, microstructure and distribution of local hardness values were strongly affected by the Mn content. The particles in Fe-25Mn and Fe-30Mn samples exhibited a distinct onion-like structure causing a considerable variability in local properties, while the particles in Fe-35Mn samples were at a glance more homogeneous, with a large volume fraction occupied by a nearly uniform material with almost constant properties.

Iron samples and Fe-Mn alloys with Mn content of 25 wt.% and 30 wt.% were prepared by blending, compressing and sintering with the aim to study their dimensional changes, microstructure, microhardness distribution and primarily the electrochemical corrosion behaviour in a simulated body environment. The light microscopy (LM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-hardness measurements revealed a microheterogeneous multiphase structure of sintered Fe-Mn samples. The potentiodynamic tests have demonstrated that the corrosion rates of such Fe-Mn alloys immersed in Hank’s solution were higher than those for a pure iron, and also higher than the rates reported for homogeneous Fe-Mn alloys.

Iron was considered a good material candidate for temporary implants in cardiovascular and orthopedic surgery. Mechanical properties of iron are attractive, however, a higher degradation rate is required. The contribution deals with the effect of silver content on microstructure and corrosion behavior of materials prepared from Ag coated iron powders. Using electroless deposition, Fe-powders with 0.29 and 2.1 wt.% of silver were prepared. Cylindrical specimens compacted at a pressure of 200 MPa were isothermally sintered at 1120°C for 60 min. The microstructure of the sintered specimens consisted of iron matrix with Ag-precipitates. The corrosion behaviour of sintered compacts was studied using the potentiodynamic polarization technique in Hank’s solution and complemented with SEM analysis. It was found out that corrosion resistance of material decreased with an increase in silver content.

The reduction processes during the sintering of Fe-3Cr-0.5Mo+0.5C pre-alloyed powder using continuous monitoring of exhaust gas composition (CO, CO2, H2O) have been identified and interpreted in relation to the density (6.5-7.4 g/cm3), sintering temperature (1120 and 1200°C), heating and cooling rates (10 and 50°C/min) and type of sintering atmosphere (10%H2-N2, N2), respectively. The progress in reduction processes was evaluated by the change in C and O contents, and fracture strength values as well. The results were compared with metallographic study of microstructure and fractographic observations of fracture surfaces. Higher sintering temperature (1200°C) and low density (3) resulted in a relative decrease in oxygen content by more than 80%. Higher cooling rate (50°C/min) eliminates re-oxidation during cooling. High density of 7.4 g/cm3,achievedby double pressing, indicated to have a negative effect on reduction processes due to restricted replenishment of the “microclimate” atmosphere with the processing gas. Higher O2 content causes weakening of interfaces with residual oxides.

A simple oxidative polymerization of pyrrole (Py) directly onto the surface of iron (Fe) microparticles was applied to increase the content of carbon in resulting material. Detection and quantification of the PPy (polypyrrole) coatings obtained were performed by means of pyrolysis gas chromatography (Py-GC). A powder consisting of such particles was compacted. The effect of PPy coating on the compressibility of coated iron powder was analysed. Namely, a set of specimens was uniaxially pressed in a steel die. Compaction pressures ranged from 50 MPa up to 600 MPa. It was found that PPy coating has a positive effect on the compaction behaviour of iron powders in the low to moderate pressure region. At higher pressures, the brittleness of PPy coating adversely affected the compressibility. Both the light and the scanning electron microscopy (LM, SEM) were used to characterize the morphology of coated powders and the microstructure of pressed samples.

The iron open cell foams were synthesized by the replication method based on powder metallurgical technologies as biodegradable bone replacement material. Open cell metal foams provide extraordinary combinations of the properties. Samples containing carbon nanotubes (CNTs) and Mg were produced with the aim to affect degradation rate and enhance the biocompatibility. The microstructure, corrosion behaviour and in vitro biocompatibilities were investigated by scanning electron microscopy, immersion tests in Hank’s solution during the time of 8 weeks, cytotoxicity and haemolysis tests. The addition of CNTs and Mg induced the higher surface inhomogeneity and roughness, which was more pronounced for Fe–Mg sample. The homogenous degradation on the whole surface was registered for bare iron sample, while progressive local corrosion sites were found on the surface of samples with CNTs and Mg. Highest corrosion rate was determined for Fe–Mg sample which came to be disintegrated after 3 weeks of immersion. The slowest degradation rate was detected for Fe–CNTs sample. The fast dieback of fibroblast cells was registered under static conditions in monolayer cell culture. However, all the experimental samples were found to be highly haemocompatible. Additionally, the haemolysis percentage value of about 2 % determined for Fe–Mg sample proved its good performance for blood vessel related cellular application.