This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Acta Metallurgica Slovaca Conference, Mar 26, 2013
Magnesium is considered as promising metal for construction of temporary biodegradable medical im... more Magnesium is considered as promising metal for construction of temporary biodegradable medical implants like stents or fixation devices for fractured bones. A biodegradable implant progressively corrodes in human body fluids and is replaced by the healing tissue. This paper presents structural, mechanical and corrosion properties of as-cast Mg, Mg-3X (in wt. %, X = Zn, Sn, Gd, Nd), AZ31 (Mg-3Al-1Zn), AJ62 (Mg-6Al-2Sr) and WE43 (Mg-4Y-3RE-0.5Zr, RE = rare earths) alloys. All the alloys were composed of α-Mg solid solution and interdendritic intermetallic phases. Hardness and tensile strength increased with incresing the total amount of alloying elements. Moreover, rare earths elements showed strong strengthening effects. The best corrosion resistance in the simulated physiological solution was observed in the case of alloys containing rare earts elements.
Acta Metallurgica Sinica (english Letters), Jun 29, 2018
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medica... more Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications. Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg-3Nd-0.5Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400°C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall-Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall-Petch of extruded Mg-3Nd-0.5Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall-Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg-3Nd-0.5Zn alloys.
Two novel ignition-resistant magnesium alloys, Mg-2Gd-2Y-1Ca and Mg-2Nd-1Y-1Ca, were prepared in ... more Two novel ignition-resistant magnesium alloys, Mg-2Gd-2Y-1Ca and Mg-2Nd-1Y-1Ca, were prepared in the ultrafine-grain condition by equal channel angular pressing (ECAP). In addition, four commercial alloys—AZ31, AX41, AE42 and WE43—were prepared similarly as a reference. The microstructure, mechanical properties and ignition temperature were thoroughly investigated. Both novel alloys exhibited a mean grain size of ~1 µm and dense distribution of small secondary phase particles. The mechanical strength measured by the tensile deformation test showed that the novel alloys are much stronger (~290 MPa) than all commercial alloys except WE43. However, Ca segregation into the grain boundaries caused a significant decrease in ductility (<6%). The ignition temperature of the novel alloys (~950 °C) was considerably improved by the presence of Gd/Nd, Y and Ca. This study showed that both novel alloys exhibit high strength and high ignition temperature in the ultrafine-grain condition.
In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn–... more 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 reac...
The sectional fire ladders, made of aluminium alloy AA6063, belong to the basic equipment of the ... more The sectional fire ladders, made of aluminium alloy AA6063, belong to the basic equipment of the fire department of the Czech Republic. The use of these materials facilitates the deployment of ladders for firefighting, but it also brings with it certain pitfalls. During the use of ladders in extinguishing fires, their thermal influence and subsequent changes in mechanical properties may occur. This is highly dangerous and can lead to people falling from these ladders due to a significant reduction in the mechanical properties of the material.
The equiatomic alloy of nickel and titanium, known as nitinol, possesses unique properties such a... more The equiatomic alloy of nickel and titanium, known as nitinol, possesses unique properties such as superelasticity, pseudoplasticity, shape memory, while maintaining good corrosion resistance and sufficient biocompatibility. Therefore it is used for production of various devices including surgery implants. Heat treatment of nickel-rich NiTi alloys can result in precipitation of nickel-rich phases, which strongly influence tensile and fatigue behaviour of the material. In this work we have studied influence of short-period heat treatment on tensile behaviour and fatigue life of the NiTi (50.9 at. % Ni) wire intended for fabrication of surgery stents.
In vitro cytotoxicity testing is an indispensable part of the development of new biomaterials. Ho... more In vitro cytotoxicity testing is an indispensable part of the development of new biomaterials. However, the standard ISO 10993-5 enables variability in the testing conditions, which makes the results of the test incomparable. We studied the influence of media composition on the results of the cytotoxicity test. Solutions of ZnCl2 served as simulated extracts and we also used extracts of three types of Zn-based and Mg-based degradable metals. We incubated the cells with the solutions prepared in two types of media with two concentrations of serum (5 and 10%). We compared the toxic effect of the extracts on L929 murine fibroblast-derived cell line, which is recommended by ISO standard and on “osteoblast-like cells” U-2 OS. We also compared two methods of exposition: solutions were added either to a sub-confluent layer or to the cell suspension. We evaluated the metabolic activity of the cells using the resazurin test. We found out that in vitro cytotoxicity is dramatically influenced ...
This paper enhances an innovative way of preparation of the composite materials by powder metallu... more This paper enhances an innovative way of preparation of the composite materials by powder metallurgy. Magnesium-fluoride composite material prepared by spark plasma sintering exerted improved corrosion resistance. Magnesium powder was coated by boiling of Mg powder in concentrated NaOH and subsequent immersion in HF. Treated powder was successfully compacted via spark plasma sintering. The composite material with a continuous network of MgF2 is prepared and it exerts improved mechanical and highly enhanced corrosion resistance compared with the pure magnesium.
Česká stomatologie/Praktické zubní lékařství, 2017
SOUHRN Úvod a cíl: Standardním materiálem užívaným pro osteosyntézu obličejového skeletu je titan... more SOUHRN Úvod a cíl: Standardním materiálem užívaným pro osteosyntézu obličejového skeletu je titan a jeho sloučeniny. Jednou z nevýhod konvenčního materiálu je nutnost jeho extrakce v indikovaných případech. Řešení situace nabízí degradovatelné materiály. V minulosti se pro tyto účely užívaly materiály na bázi polylaktidové nebo polyglykolidové kyseliny, které se klinicky prokázaly být nevyhovující. Moderním řešením je použití osteosyntetického materiálu z kovových degradovatelných slitin. Autoři prezentují původní práci-výzkum vstřebatelnosti kovových materiálů na bázi magnezia a zinku na biomodelech. Materiál a metodika: K výzkumu bylo použito celkem 12 zvířecích biomodelů-králíků, kterým byly implantovány do tibií šrouby ze tří typů kovů (dvě vstřebatelné slitiny-Zn-2Mg a WE43-a titan jako standardní materiál). Zvířata byla ve čtyřtýdenních intervalech eutanazována, vzorky kostní tkáně s implantovaným materiálem byly skenovány v mikrofokus-CT a histologicky vyšetřeny. Byla posouzena rychlost degradace materiálů. Výsledky: Doba degradace materiálu je u WE43 za fyziologických podmínek krátká pro stabilizaci fraktury do doby její konsolidace. Materiál Zn-2Mg během 16 týdnů prokázal minimální schopnost degradace. Oba materiály prokázaly přiměřené biologické vlastnosti. Závěr: Degradovatelné materiály na bázi magnezia a zinku jsou z biologického hlediska vyhovující materiály. Z výsledků výzkumu ale vyplývá, že použití obou typů slitin nevyhovuje požadavkům na materiál, tj. zachování pevnosti po dobu 12-24 týdnů a současně vstřebání v racionálním časovém rámci.
3D printing technology has recently extended to metallic materials and allows now to produce 3D m... more 3D printing technology has recently extended to metallic materials and allows now to produce 3D models directly from metallic powders. There are several methods of 3D metal printing, such as Selective Laser Sintering (SLS), Direct Metal Laser Sintering (DMLS), Electron beam melting (EBM) or Selective laser melting (SLM). Compared to conventional technologies of casting, forging and machining, these methods offer many advantages. The most important is shape variety allowing preparation of very complicated shapes and designs, which would be impossible to reach by classical techniques. Moreover, there is practically no material loss, since the remaining powder can be recycled and reused in other manufacturing processes. That is one of important cost savings. However, for now, the metal 3D printing is unable to compete the price of large-lot production. In present paper, it is demonstrated that by the SLM technology it is possible to achieve comparable material properties of stainless steel AISI 316L as by conventional technologies and therefore, this method offers a suitable alternative.
The Ni-Ti alloy (Nitinol, approx. 50 at. % Ni) is a biomaterial showing the shape memory and supe... more The Ni-Ti alloy (Nitinol, approx. 50 at. % Ni) is a biomaterial showing the shape memory and superelasticity effects. These characteristics make this material of interest for biomedical applications, especially for manufacture of stents, i.e., tubular implants for restoring damaged blood vessels, oesophageus etc. The corrosion resistance in the human body environment is a very important factor determining the life time of implants. An insufficient corrosion resistence may lead to fractures of implants, formation of dangerous fragments and to serious health problems for patients. The corrosion behavior is influenced mainly by the surface structure and chemistry of a material. But the surface state is strongly modified by chemical and heat treatment processes used in the implant manufacture. Therefore, in this study the relationships between chemical treatment and heat treatment regimes, surface state of Nitinol and its corrosion resistance in simulated physiological solution are demonstrated. It is shown that, unlike chemical pre-treatment, heat treatment used in the manufacture of stents generally negatively influences the corrosion resistance. The findings are discussed in relation to the surface state and chemistry of the material.
Selective laser melting (SLM) as a representant of additive manufacturing technology brings about... more Selective laser melting (SLM) as a representant of additive manufacturing technology brings about many advantages into production, which are appreciated especially in the field of biomedical applications and implantology. Our paper is focused on characterization of titanium alloy Ti-6Al-4V (Ti Grade 5) widely used for orthopaedic implants produced by this novel method. Microstructure and mechanical properties are compared with the same material prepared by conventional way of casting, forging and machining. Results show these are almost equivalent. Microstructure is in both cases formed by two phases +, but possesses different morphology. Yield strength and ultimate tensile strength of SLM material slightly overpassed values obtained by conventional commercial production (950 MPa and 1000 MPa vs. 877 MPa and 985 MPa). Only elongation was reduced resulting from the presence of some porosity. However, by future optimalization of SLM process parameters, porosity is expected to decrease.
The addition of Nd significantly improves the mechanical properties of magnesium alloys. However,... more The addition of Nd significantly improves the mechanical properties of magnesium alloys. However, only limited amounts of Nd or other rare earth (RE) elements should be used due to their high price. In this study, a low-alloyed Mg–1% Zn–1% Nd (ZN11) alloy was designed and processed by hot extrusion and subsequent equal-channel angular pressing (ECAP) in order to achieve a very fine-grained condition with enhanced strength. The microstructure, texture, and mechanical properties were thoroughly studied. The microstructure after 8 passes through ECAP was homogeneous and characterized by an average grain size of 1.5 µm. A large number of tiny secondary phase precipitates were identified as ordered Guinier–Preston (GP) zones. Detailed analysis of the Schmid factors revealed the effect of the texture on deformation mechanisms. ECAP processing more than doubled the achieved yield compression strength (YCS) of the ZN11 alloy. Significant strengthening by ECAP is caused by grain refinement a...
Maraging steels are generally characterized by excellent mechanical properties, which make them i... more Maraging steels are generally characterized by excellent mechanical properties, which make them ideal for various industrial applications. The application field can be further extended by using selective laser melting (SLM) for additive manufacturing of shape complicated products. However, the final mechanical properties are strongly related to the microstructure conditions. The present work studies the effect of heat treatment on the microstructure and mechanical properties of 3D printed samples prepared from powder of high-strength X3NiCoMoTi 18-9-5 maraging steel. It was found that the as-printed material had quite low mechanical properties. After sufficient heat treatment, the hardness of the material increased from 350 to 620 HV0.1 and the tensile yield strength increased from 1000 MPa up to 2000 MPa. In addition, 3% ductility was maintained. This behavior was primarily affected by strong precipitation during processing.
WE43 magnesium alloy is a commercial lightweight material developed for application at temperatur... more WE43 magnesium alloy is a commercial lightweight material developed for application at temperatures up to 250 • C. This alloy is also considered for applications in medicine as a biodegradable material. The present study provides microstructure characterization and related mechanical properties of the WE43 alloy prepared by different processing techniques including casting, extrusion, rotary swaging and heat treatment. Results indicate huge differences in observed microstructures, such as precipitation of secondary phases, grain coarsening, texture formation and also concomitant changes of mechanical properties, such as tensile yield strength, ultimate tensile strength, compressive yield strength, ultimate compressive strength and elongation to fracture. Although this material is well-known, WE43 prepared in this study by a combination of extrusion and rotary swaging offered highly improved mechanical properties, including a tensile yield strength of 370 MPa and elongation of 15 %. Such a combination of values is rarely seen in literature and is not generally offered for commercially produced materials although both preparation methods are easily commercially available.
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medica... more Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications. Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg-3Nd-0.5Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400°C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall-Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall-Petch of extruded Mg-3Nd-0.5Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall-Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg-3Nd-0.5Zn alloys.
Corrosion behaviour of magnesium and WE43 magnesium alloy in 1 M NaCl aqueous solution was studie... more Corrosion behaviour of magnesium and WE43 magnesium alloy in 1 M NaCl aqueous solution was studied by potentiodynamic polarisation and advanced acoustic emission (AE) analyses. The AE parameters suitable for the monitoring of corrosion in magnesium were shown to be the AE counts, rise time, and duration. Moreover, the mechanisms of corrosion in these materials, i.e. the ion exchange, rupture of the protective film, and the pitting corrosion were identified and their evolution was followed by the novel Adaptive sequential k-means clustering technique. The presented methods can be also suitable for monitoring of different materials and for industrial applications.
Science and Engineering of Composite Materials, 2017
Magnesium composites with suitable reinforcement such as hydroxyapatite (HA) or tricalcium phosph... more Magnesium composites with suitable reinforcement such as hydroxyapatite (HA) or tricalcium phosphate can offer improved mechanical and also biological properties, which points to them as possible candidates in medicine as biodegradable materials. The present paper deals with structure and mechanical properties of Mg-xHA (x=0, 2, 5, 10 wt.%) composites prepared from coarse Mg powder and nanoparticles of HA. Different preparation methods (milling, stamping, extrusion, spark plasma sintering) and process temperatures are combined to avoid the creation of agglomerates in structure and to reach improved mechanical properties. Hardness, compressive and three-point bending tests are performed for material characterization. On the basis of these results, authors confirm the clear effect of the volume fraction of reinforcement in composite on final properties, but authors also show even stronger effect of the preparation method on the mechanical properties of Mg-HA composites. Measured prope...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Acta Metallurgica Slovaca Conference, Mar 26, 2013
Magnesium is considered as promising metal for construction of temporary biodegradable medical im... more Magnesium is considered as promising metal for construction of temporary biodegradable medical implants like stents or fixation devices for fractured bones. A biodegradable implant progressively corrodes in human body fluids and is replaced by the healing tissue. This paper presents structural, mechanical and corrosion properties of as-cast Mg, Mg-3X (in wt. %, X = Zn, Sn, Gd, Nd), AZ31 (Mg-3Al-1Zn), AJ62 (Mg-6Al-2Sr) and WE43 (Mg-4Y-3RE-0.5Zr, RE = rare earths) alloys. All the alloys were composed of α-Mg solid solution and interdendritic intermetallic phases. Hardness and tensile strength increased with incresing the total amount of alloying elements. Moreover, rare earths elements showed strong strengthening effects. The best corrosion resistance in the simulated physiological solution was observed in the case of alloys containing rare earts elements.
Acta Metallurgica Sinica (english Letters), Jun 29, 2018
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medica... more Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications. Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg-3Nd-0.5Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400°C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall-Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall-Petch of extruded Mg-3Nd-0.5Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall-Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg-3Nd-0.5Zn alloys.
Two novel ignition-resistant magnesium alloys, Mg-2Gd-2Y-1Ca and Mg-2Nd-1Y-1Ca, were prepared in ... more Two novel ignition-resistant magnesium alloys, Mg-2Gd-2Y-1Ca and Mg-2Nd-1Y-1Ca, were prepared in the ultrafine-grain condition by equal channel angular pressing (ECAP). In addition, four commercial alloys—AZ31, AX41, AE42 and WE43—were prepared similarly as a reference. The microstructure, mechanical properties and ignition temperature were thoroughly investigated. Both novel alloys exhibited a mean grain size of ~1 µm and dense distribution of small secondary phase particles. The mechanical strength measured by the tensile deformation test showed that the novel alloys are much stronger (~290 MPa) than all commercial alloys except WE43. However, Ca segregation into the grain boundaries caused a significant decrease in ductility (<6%). The ignition temperature of the novel alloys (~950 °C) was considerably improved by the presence of Gd/Nd, Y and Ca. This study showed that both novel alloys exhibit high strength and high ignition temperature in the ultrafine-grain condition.
In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn–... more 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 reac...
The sectional fire ladders, made of aluminium alloy AA6063, belong to the basic equipment of the ... more The sectional fire ladders, made of aluminium alloy AA6063, belong to the basic equipment of the fire department of the Czech Republic. The use of these materials facilitates the deployment of ladders for firefighting, but it also brings with it certain pitfalls. During the use of ladders in extinguishing fires, their thermal influence and subsequent changes in mechanical properties may occur. This is highly dangerous and can lead to people falling from these ladders due to a significant reduction in the mechanical properties of the material.
The equiatomic alloy of nickel and titanium, known as nitinol, possesses unique properties such a... more The equiatomic alloy of nickel and titanium, known as nitinol, possesses unique properties such as superelasticity, pseudoplasticity, shape memory, while maintaining good corrosion resistance and sufficient biocompatibility. Therefore it is used for production of various devices including surgery implants. Heat treatment of nickel-rich NiTi alloys can result in precipitation of nickel-rich phases, which strongly influence tensile and fatigue behaviour of the material. In this work we have studied influence of short-period heat treatment on tensile behaviour and fatigue life of the NiTi (50.9 at. % Ni) wire intended for fabrication of surgery stents.
In vitro cytotoxicity testing is an indispensable part of the development of new biomaterials. Ho... more In vitro cytotoxicity testing is an indispensable part of the development of new biomaterials. However, the standard ISO 10993-5 enables variability in the testing conditions, which makes the results of the test incomparable. We studied the influence of media composition on the results of the cytotoxicity test. Solutions of ZnCl2 served as simulated extracts and we also used extracts of three types of Zn-based and Mg-based degradable metals. We incubated the cells with the solutions prepared in two types of media with two concentrations of serum (5 and 10%). We compared the toxic effect of the extracts on L929 murine fibroblast-derived cell line, which is recommended by ISO standard and on “osteoblast-like cells” U-2 OS. We also compared two methods of exposition: solutions were added either to a sub-confluent layer or to the cell suspension. We evaluated the metabolic activity of the cells using the resazurin test. We found out that in vitro cytotoxicity is dramatically influenced ...
This paper enhances an innovative way of preparation of the composite materials by powder metallu... more This paper enhances an innovative way of preparation of the composite materials by powder metallurgy. Magnesium-fluoride composite material prepared by spark plasma sintering exerted improved corrosion resistance. Magnesium powder was coated by boiling of Mg powder in concentrated NaOH and subsequent immersion in HF. Treated powder was successfully compacted via spark plasma sintering. The composite material with a continuous network of MgF2 is prepared and it exerts improved mechanical and highly enhanced corrosion resistance compared with the pure magnesium.
Česká stomatologie/Praktické zubní lékařství, 2017
SOUHRN Úvod a cíl: Standardním materiálem užívaným pro osteosyntézu obličejového skeletu je titan... more SOUHRN Úvod a cíl: Standardním materiálem užívaným pro osteosyntézu obličejového skeletu je titan a jeho sloučeniny. Jednou z nevýhod konvenčního materiálu je nutnost jeho extrakce v indikovaných případech. Řešení situace nabízí degradovatelné materiály. V minulosti se pro tyto účely užívaly materiály na bázi polylaktidové nebo polyglykolidové kyseliny, které se klinicky prokázaly být nevyhovující. Moderním řešením je použití osteosyntetického materiálu z kovových degradovatelných slitin. Autoři prezentují původní práci-výzkum vstřebatelnosti kovových materiálů na bázi magnezia a zinku na biomodelech. Materiál a metodika: K výzkumu bylo použito celkem 12 zvířecích biomodelů-králíků, kterým byly implantovány do tibií šrouby ze tří typů kovů (dvě vstřebatelné slitiny-Zn-2Mg a WE43-a titan jako standardní materiál). Zvířata byla ve čtyřtýdenních intervalech eutanazována, vzorky kostní tkáně s implantovaným materiálem byly skenovány v mikrofokus-CT a histologicky vyšetřeny. Byla posouzena rychlost degradace materiálů. Výsledky: Doba degradace materiálu je u WE43 za fyziologických podmínek krátká pro stabilizaci fraktury do doby její konsolidace. Materiál Zn-2Mg během 16 týdnů prokázal minimální schopnost degradace. Oba materiály prokázaly přiměřené biologické vlastnosti. Závěr: Degradovatelné materiály na bázi magnezia a zinku jsou z biologického hlediska vyhovující materiály. Z výsledků výzkumu ale vyplývá, že použití obou typů slitin nevyhovuje požadavkům na materiál, tj. zachování pevnosti po dobu 12-24 týdnů a současně vstřebání v racionálním časovém rámci.
3D printing technology has recently extended to metallic materials and allows now to produce 3D m... more 3D printing technology has recently extended to metallic materials and allows now to produce 3D models directly from metallic powders. There are several methods of 3D metal printing, such as Selective Laser Sintering (SLS), Direct Metal Laser Sintering (DMLS), Electron beam melting (EBM) or Selective laser melting (SLM). Compared to conventional technologies of casting, forging and machining, these methods offer many advantages. The most important is shape variety allowing preparation of very complicated shapes and designs, which would be impossible to reach by classical techniques. Moreover, there is practically no material loss, since the remaining powder can be recycled and reused in other manufacturing processes. That is one of important cost savings. However, for now, the metal 3D printing is unable to compete the price of large-lot production. In present paper, it is demonstrated that by the SLM technology it is possible to achieve comparable material properties of stainless steel AISI 316L as by conventional technologies and therefore, this method offers a suitable alternative.
The Ni-Ti alloy (Nitinol, approx. 50 at. % Ni) is a biomaterial showing the shape memory and supe... more The Ni-Ti alloy (Nitinol, approx. 50 at. % Ni) is a biomaterial showing the shape memory and superelasticity effects. These characteristics make this material of interest for biomedical applications, especially for manufacture of stents, i.e., tubular implants for restoring damaged blood vessels, oesophageus etc. The corrosion resistance in the human body environment is a very important factor determining the life time of implants. An insufficient corrosion resistence may lead to fractures of implants, formation of dangerous fragments and to serious health problems for patients. The corrosion behavior is influenced mainly by the surface structure and chemistry of a material. But the surface state is strongly modified by chemical and heat treatment processes used in the implant manufacture. Therefore, in this study the relationships between chemical treatment and heat treatment regimes, surface state of Nitinol and its corrosion resistance in simulated physiological solution are demonstrated. It is shown that, unlike chemical pre-treatment, heat treatment used in the manufacture of stents generally negatively influences the corrosion resistance. The findings are discussed in relation to the surface state and chemistry of the material.
Selective laser melting (SLM) as a representant of additive manufacturing technology brings about... more Selective laser melting (SLM) as a representant of additive manufacturing technology brings about many advantages into production, which are appreciated especially in the field of biomedical applications and implantology. Our paper is focused on characterization of titanium alloy Ti-6Al-4V (Ti Grade 5) widely used for orthopaedic implants produced by this novel method. Microstructure and mechanical properties are compared with the same material prepared by conventional way of casting, forging and machining. Results show these are almost equivalent. Microstructure is in both cases formed by two phases +, but possesses different morphology. Yield strength and ultimate tensile strength of SLM material slightly overpassed values obtained by conventional commercial production (950 MPa and 1000 MPa vs. 877 MPa and 985 MPa). Only elongation was reduced resulting from the presence of some porosity. However, by future optimalization of SLM process parameters, porosity is expected to decrease.
The addition of Nd significantly improves the mechanical properties of magnesium alloys. However,... more The addition of Nd significantly improves the mechanical properties of magnesium alloys. However, only limited amounts of Nd or other rare earth (RE) elements should be used due to their high price. In this study, a low-alloyed Mg–1% Zn–1% Nd (ZN11) alloy was designed and processed by hot extrusion and subsequent equal-channel angular pressing (ECAP) in order to achieve a very fine-grained condition with enhanced strength. The microstructure, texture, and mechanical properties were thoroughly studied. The microstructure after 8 passes through ECAP was homogeneous and characterized by an average grain size of 1.5 µm. A large number of tiny secondary phase precipitates were identified as ordered Guinier–Preston (GP) zones. Detailed analysis of the Schmid factors revealed the effect of the texture on deformation mechanisms. ECAP processing more than doubled the achieved yield compression strength (YCS) of the ZN11 alloy. Significant strengthening by ECAP is caused by grain refinement a...
Maraging steels are generally characterized by excellent mechanical properties, which make them i... more Maraging steels are generally characterized by excellent mechanical properties, which make them ideal for various industrial applications. The application field can be further extended by using selective laser melting (SLM) for additive manufacturing of shape complicated products. However, the final mechanical properties are strongly related to the microstructure conditions. The present work studies the effect of heat treatment on the microstructure and mechanical properties of 3D printed samples prepared from powder of high-strength X3NiCoMoTi 18-9-5 maraging steel. It was found that the as-printed material had quite low mechanical properties. After sufficient heat treatment, the hardness of the material increased from 350 to 620 HV0.1 and the tensile yield strength increased from 1000 MPa up to 2000 MPa. In addition, 3% ductility was maintained. This behavior was primarily affected by strong precipitation during processing.
WE43 magnesium alloy is a commercial lightweight material developed for application at temperatur... more WE43 magnesium alloy is a commercial lightweight material developed for application at temperatures up to 250 • C. This alloy is also considered for applications in medicine as a biodegradable material. The present study provides microstructure characterization and related mechanical properties of the WE43 alloy prepared by different processing techniques including casting, extrusion, rotary swaging and heat treatment. Results indicate huge differences in observed microstructures, such as precipitation of secondary phases, grain coarsening, texture formation and also concomitant changes of mechanical properties, such as tensile yield strength, ultimate tensile strength, compressive yield strength, ultimate compressive strength and elongation to fracture. Although this material is well-known, WE43 prepared in this study by a combination of extrusion and rotary swaging offered highly improved mechanical properties, including a tensile yield strength of 370 MPa and elongation of 15 %. Such a combination of values is rarely seen in literature and is not generally offered for commercially produced materials although both preparation methods are easily commercially available.
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medica... more Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications. Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg-3Nd-0.5Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400°C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall-Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall-Petch of extruded Mg-3Nd-0.5Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall-Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg-3Nd-0.5Zn alloys.
Corrosion behaviour of magnesium and WE43 magnesium alloy in 1 M NaCl aqueous solution was studie... more Corrosion behaviour of magnesium and WE43 magnesium alloy in 1 M NaCl aqueous solution was studied by potentiodynamic polarisation and advanced acoustic emission (AE) analyses. The AE parameters suitable for the monitoring of corrosion in magnesium were shown to be the AE counts, rise time, and duration. Moreover, the mechanisms of corrosion in these materials, i.e. the ion exchange, rupture of the protective film, and the pitting corrosion were identified and their evolution was followed by the novel Adaptive sequential k-means clustering technique. The presented methods can be also suitable for monitoring of different materials and for industrial applications.
Science and Engineering of Composite Materials, 2017
Magnesium composites with suitable reinforcement such as hydroxyapatite (HA) or tricalcium phosph... more Magnesium composites with suitable reinforcement such as hydroxyapatite (HA) or tricalcium phosphate can offer improved mechanical and also biological properties, which points to them as possible candidates in medicine as biodegradable materials. The present paper deals with structure and mechanical properties of Mg-xHA (x=0, 2, 5, 10 wt.%) composites prepared from coarse Mg powder and nanoparticles of HA. Different preparation methods (milling, stamping, extrusion, spark plasma sintering) and process temperatures are combined to avoid the creation of agglomerates in structure and to reach improved mechanical properties. Hardness, compressive and three-point bending tests are performed for material characterization. On the basis of these results, authors confirm the clear effect of the volume fraction of reinforcement in composite on final properties, but authors also show even stronger effect of the preparation method on the mechanical properties of Mg-HA composites. Measured prope...
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Papers by Jiří Kubásek