The increasing incidence of trauma in medicine brings with it new demands on the materials used f... more 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...
Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficie... more Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficient mechanical properties (for some applications) or low biocompatible Zn2+ concentrations can be modified by the alloying by essential elements like magnesium, calcium or strontium. The alloying elements also enhance the biocompatibility of zinc due to a decrease of Zn2+ release which could be toxic in a concentration exceeding 100 µM. In this study, the microstructure and hardness of a potentially biodegradable alloy ZnMg0.8Ca0.2 were observed in relation to different cooling rates. It was found that zinc dendrites, Mg2Zn11 (MgZn2) and CaZn13 phases occur in the material structure. The micro-hardness measurements revealed constant hardness of the particular phases; however, the macro-harness slightly decreased with the decreasing cooling rate due to changes in phase sizes and distribution. The obtained information allows to optimize the preparation process in order to reach optimal prop...
A NiTi shape memory alloy, known as nitinol, has been intensively studied for last five decades. ... more A NiTi shape memory alloy, known as nitinol, has been intensively studied for last five decades. This big interest is caused by its unique properties, such as pseudoplasticity, superelasticity, shape memory, as well as good corrosion resistance and sufficient biocompatibility. Unfortunately, its common manufacture methods (vacuum induction melting, vacuum arc remelting) possess some disadvantages, such as a contamination or an insufficient homogeneity of the fabricated ingots. Therefore, new fabrication methods have been recently intensively studied. The self-propagating high-temperature synthesis seems to be a promising approach to the NiTi fabrication. It has been performed in both (thermal explosion and plane wave propagation) regimes. The thermal explosion one seems to be more suitable for the fabrication of compact materials. In this work, the NiTi samples were prepared by the thermal explosion mode of self-propagating hightemperature synthesis (TE-SHS). The influence of a sint...
Magnesium is a biocompatible and biodegradable metal which possesses suitable mechanical properti... more Magnesium is a biocompatible and biodegradable metal which possesses suitable mechanical properties for load-bearing applications in orthopaedics. Moreover, magnesium ions, the products of magnesium corrosion, improve growth of the new bone tissue. Implementation of the porosity into these materials compromises values of mechanical properties closer to the values of nature bone and allows the incorporation of the new tissue into the implant and the transport of body fluids to the healing tissue. In this work porous magnesium samples with the porosity of approximately 11, 14, 26, 29 and 44% were prepared and their structures and flexural strengths were studied.
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 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 this paper we focused on the influence of sintering conditions; purity of argon atmosphere and... more In this paper we focused on the influence of sintering conditions; purity of argon atmosphere and sintering time namely, on microstructural and mechanical characteristics of porous magnesium prepared by powder metallurgy. An argon with technical purity (99.996 vol.%) and argon purified by a magnesium getter were used as the sintering atmospheres. The samples were sintered for different times (0, 3, 6, 12 and 24 h). Subsequently, microstructure, flexural and compressive behaviour were investigated in detail. The type of used atmosphere had no significant influence on the studied characteristics after sintering up to 6 h and the mechanical properties increased with longer sintering time. On the other hand, after sintering longer than 6 h, mechanical properties of the samples sintered under the purified atmosphere increased with longer sintering time, while the use of technical argon decreased mechanical properties significantly and slightly increased porosity. It was caused by oxidati...
Jiří Kubásek1, Drahomír Dvorský1, Jaroslav Čapek2, Straková Markéta1, Hosová Klára1, Dalibor Vojt... more Jiří Kubásek1, Drahomír Dvorský1, Jaroslav Čapek2, Straková Markéta1, Hosová Klára1, Dalibor Vojtěch1 1University of Chemistry and Technology Prague, Faculty of Chemical Technology, Department of Metals and Corrosion Engineering, Technická 5 166 28 Praha 6 – Dejvice, Czech Republic., E-mail: kubasekj@vscht.cz 2FZU – The Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, Prague 8, 182 21, The Czech Republic
Geometric aspects of the shear processes in hexagonal metals are analysed. They can be divided in... more Geometric aspects of the shear processes in hexagonal metals are analysed. They can be divided into three groups: those localized essentially between neighbouring atomic planes, occurring in narrow slabs along particular atomic planes, or covering a large crystal volume. Obviously, dislocation glide and deformation twinning are principal types of such processes. On the geometrical level, the dislocation slip as well as twin propagation are controlled by Schmid factors. Since the sample loaded by external stress can sometimes give way to fracture (cleavage) under tensile stress, it has to be also mentioned. The main aim of this work is to show only on geometrical grounds for which sample orientation which process is more likely to occur. More complex shear processes that take place during double twinning are also briefly considered. In polycrystals, the shear phenomena lead to texture formation when the processes that control the behaviour of materials may be those that act in a simi...
Hořčík je lehký kov bělošedé barvy. V zemské kůře je šestým nejrozšířenějším prvkem. V přírodě se... more Hořčík je lehký kov bělošedé barvy. V zemské kůře je šestým nejrozšířenějším prvkem. V přírodě se nejvíce nachází ve formě chloridu hořečnatého v mořské vodě. Je velmi lehký, jeho hustota je 1738 kg m. Ve formě rozmanitých sloučenin se běžně používá jako součást léků či potravinových doplňků. Jeho toxicita pro lidský organismus je v porovnání s jinými kovy poměrně malá. Hořčík je široce využíván rovněž v kovové formě, a to jako hlavní součást lehkých slitin určených zejména pro výrobu součástek automobilů, letadel a dalších dopravních prostředků. Z chemického hlediska je kovový hořčík poměrně reaktivní, což přináší problémy při jeho výrobě, zpracování i používání. Tavení, odlévání i svařování hořčíkových slitin se z důvodu reaktivity musí provádět pod ochrannou atmosférou obsahující např. inertní plyny nebo fluorid sírový SF6. Také hořčíkové součástky vystavené agresivnímu venkovnímu prostředí musejí být proti korozi chráněny vhodnými povlaky. Chemická reaktivita hořčíku však může v...
Approximately an equiatomic alloy of nickel and titanium, known as nitinol, possesses a lot of in... more Approximately an equiatomic alloy of nickel and titanium, known as nitinol, possesses a lot of interesting properties such as superelasticity, pseudoplasticity, shape memory, good corrosion resistance and satisfactory biocompatibility. Therefore, it is used in a lot of branches, for example for fabrication of surgery implants. Due to disadvantages of commonly used manufacture methods, there is a search for their alternatives. Powder metallurgy can be one of them. In this work, influence of particle size of initial powders on composition and properties of samples, which were prepared by a thermal explosion mode of self-propagating high-temperature synthesis (TE – SHS) powder metallurgy technique, was studied.
In this study, we prepared zinc wires with a diameter of 250 µm by direct extrusion using an extr... more 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 siz...
Abstract In this paper, the effect of laser shock peening (LSP) of mono- and polycrystalline copp... more Abstract In this paper, the effect of laser shock peening (LSP) of mono- and polycrystalline copper was studied. It is shown that the residual stress caused by this process is accumulated at the LSP treated surface of the material, the thickness of which is several hundreds of micrometers. The affected layer contains an enhanced density of dislocations. These dislocations are homogeneously distributed on the cross-section in the single crystal along the single slip plane. The dislocations in the polycrystal are distributed heterogeneously on the sample cross-section. This heterogeneity is discussed from the viewpoint of the orientation dependence of individual grains and varied values of the Schmid factor and confirms the compressive nature of the stress caused by LSP. Depth dependence of the microhardness of the material decreases from the LSP treated surface in direction to the sample center correspondingly.
A new severe plastic deformation technique, known as the complex shearing of extruded tube (CSET)... more 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.
Zinc and its alloys seem to be promising candidates for biodegradable applications. Those materia... more 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 rat...
IOP Conference Series: Materials Science and Engineering
3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produc... more 3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produce components of very complicated shapes from various kinds of materials. In this work a highly porous (porosity of almost 90 vol. %) stainless steel component was manufactured by SLM. The material was characterized in terms of structure, surface chemistry and mechanical properties. It was observed that mechanical properties of the material were similar to those of trabecular human bone. The tests realized in this work confirmed suitability of the porous material prepared by SLM for the use in medicine, for example, for scaffolds designed to repair bone defects.
Abstract In this study, the nano-crystalline Nitinol (50.9 at.% Ni) was prepared by 40% cold defo... more Abstract In this study, the nano-crystalline Nitinol (50.9 at.% Ni) was prepared by 40% cold deformation. Subsequently it was subjected to 15-min-heat treatments at 300–550 °C. Changes of the structure and mechanical properties were studied by transmission electron microscopy, micro X-ray diffraction, differential scanning calorimetry, Vickers hardness measurements, tensile and bend-type fatigue testing. It was shown that the cold drawn material contains textured nano-crystalline B2 grains of 50 nm in thickness and a high concentration of lattice defects. Its tensile strength, hardness and fatigue life were 1521 MPa, 421 HV0.05 and 2435 bending cycles to fracture, respectively. After heat-treatment up to 450 °C/15 min the material underwent Ni4Ti3 precipitation and partial recovery processes. Heat-treatments at above 450 °C induced recrystallization, grain and precipitate growth. Hardness and fatigue lives showed maxima of 692 HV0.05 and 5883 cycles, respectively, after heat-treatments at 450 °C/15 min. In contrast, both tensile strength and B2 → B19′ transformation stress decreased with increasing heat-treatment temperature, but a decrease of the tensile strength after heat-treatments at 300–450 °C was slow (tensile strength after heat-treatment at 450 °C/15 min was 1486 MPa). The observed variations of mechanical characteristics were discussed in relation to structural changes observed.
There is currently an increasing demand for metals with a hexagonal close-packed structure (HCP) ... more There is currently an increasing demand for metals with a hexagonal close-packed structure (HCP) [...]
The increasing incidence of trauma in medicine brings with it new demands on the materials used f... more 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...
Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficie... more Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficient mechanical properties (for some applications) or low biocompatible Zn2+ concentrations can be modified by the alloying by essential elements like magnesium, calcium or strontium. The alloying elements also enhance the biocompatibility of zinc due to a decrease of Zn2+ release which could be toxic in a concentration exceeding 100 µM. In this study, the microstructure and hardness of a potentially biodegradable alloy ZnMg0.8Ca0.2 were observed in relation to different cooling rates. It was found that zinc dendrites, Mg2Zn11 (MgZn2) and CaZn13 phases occur in the material structure. The micro-hardness measurements revealed constant hardness of the particular phases; however, the macro-harness slightly decreased with the decreasing cooling rate due to changes in phase sizes and distribution. The obtained information allows to optimize the preparation process in order to reach optimal prop...
A NiTi shape memory alloy, known as nitinol, has been intensively studied for last five decades. ... more A NiTi shape memory alloy, known as nitinol, has been intensively studied for last five decades. This big interest is caused by its unique properties, such as pseudoplasticity, superelasticity, shape memory, as well as good corrosion resistance and sufficient biocompatibility. Unfortunately, its common manufacture methods (vacuum induction melting, vacuum arc remelting) possess some disadvantages, such as a contamination or an insufficient homogeneity of the fabricated ingots. Therefore, new fabrication methods have been recently intensively studied. The self-propagating high-temperature synthesis seems to be a promising approach to the NiTi fabrication. It has been performed in both (thermal explosion and plane wave propagation) regimes. The thermal explosion one seems to be more suitable for the fabrication of compact materials. In this work, the NiTi samples were prepared by the thermal explosion mode of self-propagating hightemperature synthesis (TE-SHS). The influence of a sint...
Magnesium is a biocompatible and biodegradable metal which possesses suitable mechanical properti... more Magnesium is a biocompatible and biodegradable metal which possesses suitable mechanical properties for load-bearing applications in orthopaedics. Moreover, magnesium ions, the products of magnesium corrosion, improve growth of the new bone tissue. Implementation of the porosity into these materials compromises values of mechanical properties closer to the values of nature bone and allows the incorporation of the new tissue into the implant and the transport of body fluids to the healing tissue. In this work porous magnesium samples with the porosity of approximately 11, 14, 26, 29 and 44% were prepared and their structures and flexural strengths were studied.
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 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 this paper we focused on the influence of sintering conditions; purity of argon atmosphere and... more In this paper we focused on the influence of sintering conditions; purity of argon atmosphere and sintering time namely, on microstructural and mechanical characteristics of porous magnesium prepared by powder metallurgy. An argon with technical purity (99.996 vol.%) and argon purified by a magnesium getter were used as the sintering atmospheres. The samples were sintered for different times (0, 3, 6, 12 and 24 h). Subsequently, microstructure, flexural and compressive behaviour were investigated in detail. The type of used atmosphere had no significant influence on the studied characteristics after sintering up to 6 h and the mechanical properties increased with longer sintering time. On the other hand, after sintering longer than 6 h, mechanical properties of the samples sintered under the purified atmosphere increased with longer sintering time, while the use of technical argon decreased mechanical properties significantly and slightly increased porosity. It was caused by oxidati...
Jiří Kubásek1, Drahomír Dvorský1, Jaroslav Čapek2, Straková Markéta1, Hosová Klára1, Dalibor Vojt... more Jiří Kubásek1, Drahomír Dvorský1, Jaroslav Čapek2, Straková Markéta1, Hosová Klára1, Dalibor Vojtěch1 1University of Chemistry and Technology Prague, Faculty of Chemical Technology, Department of Metals and Corrosion Engineering, Technická 5 166 28 Praha 6 – Dejvice, Czech Republic., E-mail: kubasekj@vscht.cz 2FZU – The Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, Prague 8, 182 21, The Czech Republic
Geometric aspects of the shear processes in hexagonal metals are analysed. They can be divided in... more Geometric aspects of the shear processes in hexagonal metals are analysed. They can be divided into three groups: those localized essentially between neighbouring atomic planes, occurring in narrow slabs along particular atomic planes, or covering a large crystal volume. Obviously, dislocation glide and deformation twinning are principal types of such processes. On the geometrical level, the dislocation slip as well as twin propagation are controlled by Schmid factors. Since the sample loaded by external stress can sometimes give way to fracture (cleavage) under tensile stress, it has to be also mentioned. The main aim of this work is to show only on geometrical grounds for which sample orientation which process is more likely to occur. More complex shear processes that take place during double twinning are also briefly considered. In polycrystals, the shear phenomena lead to texture formation when the processes that control the behaviour of materials may be those that act in a simi...
Hořčík je lehký kov bělošedé barvy. V zemské kůře je šestým nejrozšířenějším prvkem. V přírodě se... more Hořčík je lehký kov bělošedé barvy. V zemské kůře je šestým nejrozšířenějším prvkem. V přírodě se nejvíce nachází ve formě chloridu hořečnatého v mořské vodě. Je velmi lehký, jeho hustota je 1738 kg m. Ve formě rozmanitých sloučenin se běžně používá jako součást léků či potravinových doplňků. Jeho toxicita pro lidský organismus je v porovnání s jinými kovy poměrně malá. Hořčík je široce využíván rovněž v kovové formě, a to jako hlavní součást lehkých slitin určených zejména pro výrobu součástek automobilů, letadel a dalších dopravních prostředků. Z chemického hlediska je kovový hořčík poměrně reaktivní, což přináší problémy při jeho výrobě, zpracování i používání. Tavení, odlévání i svařování hořčíkových slitin se z důvodu reaktivity musí provádět pod ochrannou atmosférou obsahující např. inertní plyny nebo fluorid sírový SF6. Také hořčíkové součástky vystavené agresivnímu venkovnímu prostředí musejí být proti korozi chráněny vhodnými povlaky. Chemická reaktivita hořčíku však může v...
Approximately an equiatomic alloy of nickel and titanium, known as nitinol, possesses a lot of in... more Approximately an equiatomic alloy of nickel and titanium, known as nitinol, possesses a lot of interesting properties such as superelasticity, pseudoplasticity, shape memory, good corrosion resistance and satisfactory biocompatibility. Therefore, it is used in a lot of branches, for example for fabrication of surgery implants. Due to disadvantages of commonly used manufacture methods, there is a search for their alternatives. Powder metallurgy can be one of them. In this work, influence of particle size of initial powders on composition and properties of samples, which were prepared by a thermal explosion mode of self-propagating high-temperature synthesis (TE – SHS) powder metallurgy technique, was studied.
In this study, we prepared zinc wires with a diameter of 250 µm by direct extrusion using an extr... more 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 siz...
Abstract In this paper, the effect of laser shock peening (LSP) of mono- and polycrystalline copp... more Abstract In this paper, the effect of laser shock peening (LSP) of mono- and polycrystalline copper was studied. It is shown that the residual stress caused by this process is accumulated at the LSP treated surface of the material, the thickness of which is several hundreds of micrometers. The affected layer contains an enhanced density of dislocations. These dislocations are homogeneously distributed on the cross-section in the single crystal along the single slip plane. The dislocations in the polycrystal are distributed heterogeneously on the sample cross-section. This heterogeneity is discussed from the viewpoint of the orientation dependence of individual grains and varied values of the Schmid factor and confirms the compressive nature of the stress caused by LSP. Depth dependence of the microhardness of the material decreases from the LSP treated surface in direction to the sample center correspondingly.
A new severe plastic deformation technique, known as the complex shearing of extruded tube (CSET)... more 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.
Zinc and its alloys seem to be promising candidates for biodegradable applications. Those materia... more 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 rat...
IOP Conference Series: Materials Science and Engineering
3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produc... more 3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produce components of very complicated shapes from various kinds of materials. In this work a highly porous (porosity of almost 90 vol. %) stainless steel component was manufactured by SLM. The material was characterized in terms of structure, surface chemistry and mechanical properties. It was observed that mechanical properties of the material were similar to those of trabecular human bone. The tests realized in this work confirmed suitability of the porous material prepared by SLM for the use in medicine, for example, for scaffolds designed to repair bone defects.
Abstract In this study, the nano-crystalline Nitinol (50.9 at.% Ni) was prepared by 40% cold defo... more Abstract In this study, the nano-crystalline Nitinol (50.9 at.% Ni) was prepared by 40% cold deformation. Subsequently it was subjected to 15-min-heat treatments at 300–550 °C. Changes of the structure and mechanical properties were studied by transmission electron microscopy, micro X-ray diffraction, differential scanning calorimetry, Vickers hardness measurements, tensile and bend-type fatigue testing. It was shown that the cold drawn material contains textured nano-crystalline B2 grains of 50 nm in thickness and a high concentration of lattice defects. Its tensile strength, hardness and fatigue life were 1521 MPa, 421 HV0.05 and 2435 bending cycles to fracture, respectively. After heat-treatment up to 450 °C/15 min the material underwent Ni4Ti3 precipitation and partial recovery processes. Heat-treatments at above 450 °C induced recrystallization, grain and precipitate growth. Hardness and fatigue lives showed maxima of 692 HV0.05 and 5883 cycles, respectively, after heat-treatments at 450 °C/15 min. In contrast, both tensile strength and B2 → B19′ transformation stress decreased with increasing heat-treatment temperature, but a decrease of the tensile strength after heat-treatments at 300–450 °C was slow (tensile strength after heat-treatment at 450 °C/15 min was 1486 MPa). The observed variations of mechanical characteristics were discussed in relation to structural changes observed.
There is currently an increasing demand for metals with a hexagonal close-packed structure (HCP) ... more There is currently an increasing demand for metals with a hexagonal close-packed structure (HCP) [...]
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Papers by Jaroslav Čapek