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Depth profile analysis of a hydrogenated Ti–6Al–4V alloy by glow discharge optical emission spectroscopy (GDOES) is described. Besides the earlier reported 'hydrogen effects', causing changes in emission intensities of other elements if hydrogen is present, the analysis of hydrogen itself was found to be affected by the redistribution of hydrogen in the region adjacent to the analyzed spot, due to sample heating and the thereby increased hydrogen diffusivity. A simple model of heat transfer within the sample during the GDOES analysis is proposed and the surface temperature of the analyzed spot is estimated to be ≈365 °C, in the given experimental setup. [ABSTRACT FROM AUTHOR]

Zinc based materials have been studied as candidates for the fabrication of biodegradable implants. For applications in orthopedics, porous materials with reduced modulus of elasticity are desirable. Fabrication of porous zinc is challenging due to several processing difficulties, such as low melting point, easy evaporation and high reactivity with many porogen agents. In this work, we prepared a porous zinc sheet by thermal plasma spraying with a porosity of 16.8%. Mechanical, corrosion and biological characteristics of the prepared material were studied in detail. The porous zinc possessed reduced moduli of elasticity (2-6 GPa) and relatively high values of strengths (12-55 MPa—depending on the loading mode). The corrosion rate of the porous zinc was approximately 0.1 mm/a, and the extracts showed excellent murine L929 cell viability. The results suggest that thermal plasma spraying is usable for preparation of biodegradable porous zinc scaffolds. [ABSTRACT FROM AUTHOR]

secondary twinning inside a primary twin has been observed on the (0001) fracture surface of zinc after quenching of a single crystal grown by the Bridgman method. This type of double twinning was previously observed in magnesium with a quite different c/a axial ratio. A geometrical analysis is presented that can explain why the observed secondary twins are activated. [ABSTRACT FROM AUTHOR]

Recently, zinc-based materials have been extensively investigated as materials suitable for the fabrication of biodegradable orthopedic implants. In this study, porous zinc was prepared as a material for implantation into trabecular bone using spark plasma sintering with different sizes of initial zinc powders, and microstructural, mechanical and corrosion characterizations of the prepared materials were performed. The porosity of the prepared porous samples was approximately 20%. The mechanical properties depended on the initial powder particle size, the pore size and distribution. By using a finer powder (FP), <100 μm in size, the compressive yield strength and the compressive modulus were approximately 31.2 MPa and 1.2 GPa, respectively. These values approach those of trabecular bone (1–12 MPa and 0.1–0.4 GPa). Moreover, the plastic deformation of FP materials occurred at almost constant stress similar to trabecular bone. The corrosion rates of the porous Zn were 0.6–0.8 mm/a and depended on the initial powder particle size, the pore size and distribution. After pre-incubation of the porous Zn in simulated body fluid (SBF), the Zn concentration in biological extracts was below the toxic limit of zinc for L929 cells. Based on the obtained results, we can estimate that the materials prepared from the finer zinc powder showed properties suitable for the fabrication of porous biodegradable orthopedic implants. [ABSTRACT FROM AUTHOR]

Recently, iron-based materials have been considered as candidates for the fabrication of biodegradable load-bearing implants. Alloying with palladium has been found to be a suitable approach to enhance the insufficient corrosion rate of iron-based alloys. In this work, we have extensively compared the microstructure, the mechanical and corrosion properties, and the cytotoxicity of an FePd2 (wt%) alloy prepared by three different routes — casting, mechanical alloying and spark plasma sintering (SPS), and mechanical alloying and the space holder technique (SHT). The properties of the FePd2 (wt%) were compared with pure Fe prepared in the same processes. The preparation route significantly influenced the material properties. Materials prepared by SPS possessed the highest values of mechanical properties (CYS ~ 750–850 MPa) and higher corrosion rates than the casted materials. Materials prepared by SHT contained approximately 60% porosity; therefore, their mechanical properties reached the lowest values, and they had the highest corrosion rates, approximately 0.7–1.2 mm/a. Highly porous FePd2 was tested in vitro according to the ISO 10993-5 standard using L929 cells, and two-fold diluted extracts showed acceptable cytocompatibility. In general, alloying with Pd enhanced both mechanical properties and corrosion rates and did not decrease the cytocompatibility of the studied materials. [ABSTRACT FROM AUTHOR]

Recently, porous metallic materials have been extensively studied as candidates for use in the fabrication of scaffolds and augmentations to repair trabecular bone defects, e.g. in surroundings of joint replacements. Fabricating these complex structures by using common approaches (e.g., casting and machining) is very challenging. Therefore, rapid prototyping techniques, such as selective laser melting (SLM), have been investigated for these applications. In this study, we characterized a highly porous (87 vol.%) 316L stainless steel scaffold prepared by SLM. 316L steel was chosen because it presents a biomaterial still widely used for fabrication of joint replacements and, from the practical point of view, use of the same material for fabrication of an augmentation and a joint replacement is beneficial for corrosion prevention. The results are compared to the reported properties of two representative nonporous 316L stainless steels prepared either by SLM or casting and subsequent hot forging. The microstructural and mechanical properties and the surface chemical composition and interaction with the cells were investigated. The studied material exhibited mechanical properties that were similar to those of trabecular bone (compressive modulus of elasticity ~ 0.15 GPa, compressive yield strength ~ 3 MPa) and cytocompatibility after one day that was similar to that of wrought 316L stainless steel, which is a commonly used biomaterial. Based on the obtained results, SLM is a suitable method for the fabrication of porous 316L stainless steel scaffolds with highly porous structures. [ABSTRACT FROM AUTHOR]

Research on biodegradable iron-based materials has been increasing because they appear suitable for fabrication of temporary orthopedic and cardiovascular implants. Preliminary in vitro and in vivo studies have found that iron and some of its alloys exhibit good cyto- and biocompatibility. The main disadvantage of pure iron is its insufficient corrosion rate in physiological environments; therefore, it is necessary to modify it by suitable alloying. In this study, iron alloys containing 2 wt % of palladium, silver or carbon were prepared using powder metallurgy. The microstructure, mechanical and corrosion properties in a simulated body fluid were characterized. Compared to pure iron, alloying slightly increased porosity (from 15% to ∼ 18%) and decreased the compressive modulus of elasticity (from 5.6 to 1.1–1.8 GPa), compressive proof strength (from 145 to 113–127 MPa) and the Vickers hardness (from 63 to 23–37). Alloying with palladium and carbon enhanced (whereas silver lowered) the corrosion rate of iron in a simulated body fluid. Based on the obtained results, carbon and especially palladium appear to be suitable alloying elements for iron-based biodegradable materials. [ABSTRACT FROM AUTHOR]

An interest in biodegradable metallic materials has been increasing in the last two decades. Besides magnesium based materials, iron-manganese alloys have been considered as possible candidates for fabrication of biodegradable stents and orthopedic implants. In this study, we prepared a hot forged FeMn30 (wt.%) alloy and investigated its microstructural, mechanical and corrosion characteristics as well as cytotoxicity towards mouse L 929 fibroblasts. The obtained results were compared with those of iron. The FeMn30 alloy was composed of antiferromagnetic γ-austenite and ε-martensite phases and possessed better mechanical properties than iron and even that of 316L steel. The potentiodynamic measurements in simulated body fluids showed that alloying with manganese lowered the free corrosion potential and enhanced the corrosion rate, compared to iron. On the other hand, the corrosion rate of FeMn30 obtained by a semi-static immersion test was significantly lower than that of iron, most likely due to a higher degree of alkalization in sample surrounding. The presence of manganese in the alloy slightly enhanced toxicity towards the L 929 cells; however, the toxicity did not exceed the allowed limit and FeMn30 alloy fulfilled the requirements of the ISO 10993-5 standard. [ABSTRACT FROM AUTHOR]

Research into biodegradable porous materials has been increasingly focused on iron-based materials because such materials possess suitable properties for orthopedic applications. In this study, we prepared porous iron with porosities of 32-82 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied the influence of initial powder size and compacting pressure on sample microstructure, contamination and mechanical characteristics. The experimental results were analyzed as well, using Gibson-Ashby model and this analysis showed a good agreement in theoretical and experimental data. Whereas increasing compression pressure decreased porosity, the use of finer iron powder led to an increase in porosity. Increasing the amount of space-holder material in the initial mixture increased the total porosity, improved compressibility and consequently decreased the number of pores originating from imperfect compaction. A higher compacting pressure and the use of finer powder enhanced both the flexural and compressive properties. Even the most porous samples prepared from the fine iron powder possessed mechanical properties comparable to human cancellous bone. Based on these results, we can claim that the use of fine initial iron powder is necessary to obtain highly porous iron, which appears to be suitable for orthopedic applications. [ABSTRACT FROM AUTHOR]

The demand for porous biodegradable load-bearing implants has been increasing recently. Based on investigations of biodegradable stents, porous iron may be a suitable material for such applications. In this study, we prepared porous iron samples with porosities of 34–51 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied sample microstructure (SEM-EDX and XRD), flexural and compressive behaviors (universal loading machine) and hardness HV5 (hardness tester) of the prepared samples. Sample porosity increased with the amount of spacer in the initial mixtures. Only the pore surfaces had insignificant oxidation and no other contamination was observed. Increasing porosity decreased the mechanical properties of the samples; although, the properties were still comparable with human bone and higher than those of porous non-metallic biomaterials and porous magnesium prepared in a similar way. Based on these results, powder metallurgy appears to be a suitable method for the preparation of porous iron for orthopedic applications. [ABSTRACT FROM AUTHOR]

Abstract: There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium. [Copyright &y& Elsevier]

Abstract: Porous magnesium-based materials are biodegradable and promising for use in orthopaedic applications, but their applications are hampered by their difficult fabrication. This work reports the preparation of porous magnesium materials by a powder metallurgy technique using ammonium bicarbonate as spacer particles. The porosity of the materials depended on the amount of ammonium bicarbonate and was found to have strong negative effects on flexural strength and corrosion behaviour. However, the flexural strength of materials with porosities of up to 28vol.% was higher than the flexural strength of non-metallic biomaterials and comparable with that of natural bone. [Copyright &y& Elsevier]

Zinc (Zn) alloys seem to be promising candidates for application in orthopaedic or cardiovascular medical implants. In this area, high standards are required regarding the biocompatibility as well as excellent mechanical and tailored degradation properties. In the presented study, a novel Zn-0.8Mg-0.2Sr (wt%) alloy has been fabricated by the combination of casting, homogenization annealing and extrusion at 200 °C. As a consequence of its fine-grained homogenous microstructure, the prepared material is characterized by an excellent combination of tensile yield strength, ultimate tensile strength and elongation corresponding to 244 MPa, 324 MPa and 20% respectively. The in vitro corrosion rates of the Zn-0.8Mg-0.2Sr alloy in the physiological solution and the simulated body fluid were 244 μm/a and 69.8 μm/a, respectively. Furthermore, an extract test revealed that Zn-0.8Mg-0.2Sr extracts diluted to 25% had no adverse effects towards L929 fibroblasts, TAg periosteal cells and Saos-2 osteoblasts. Moreover, the Zn-0.8Mg-0.2Sr surface showed effective inhibition of initial Streptococcus gordonii adhesion and biofilm formation. These results indicated the Zn-0.8Mg-0.2Sr alloy, which has superior mechanical properties, might be a promising candidate for materials used for load-bearing applications. Unlabelled Image • A novel Zn-0.8Mg-0.2Sr (wt%) alloy was fabricated and investigated. • As-extruded Zn-0.8Mg-0.2Sr alloy exhibited superior mechanical properties. • Enhanced Zn ion release from Zn-0.8Mg-0.2Sr alloy was observed compared to pure Zn. • Zn-0.8Mg-0.2Sr extracts showed acceptable cytocompatibility. • Zn-0.8Mg-0.2Sr surface possessed effective antibacterial property. [ABSTRACT FROM AUTHOR]

The complex study of the mechanical properties of pure iron produced by selective laser melting (SLM) revealed enhanced values of the yield stress and ultimate tensile strength as compared to the material produced in a classic way. These values result from high dislocation density, presence of interstitial carbon and small precipitates. In-situ tensile experiments revealed that the basic mechanism of plastic deformation in this material, the structure of which was described in detail previously Mater. Charact. 154 (2019) 222], is the emission of dislocations from dislocation walls in the material. From the yield drop at the stress-strain dependence, the effective binding energy of carbon to dislocations is estimated. SLM iron also exhibits anisotropy of nanohardness showing maxima for orientations in the middle of the orientation triangle but also at {100} and {110} corners. This anisotropy suggests that the deformation is affected by the splitting of ½⟨111⟩ dislocations on {110} planes into partials on {112} planes. Image 1 • Deformation of SLM iron consists of emission of dislocations from dislocation walls, solute atmosphere and small particles. • The effective binding energy of carbon to dislocations was determined. • Anisotropy of nanohardness supports the complex behavior of dislocations in bcc iron. [ABSTRACT FROM AUTHOR]

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

Zinc-based alloys containing the elements of the second group of the periodic table have been extensively studied as potential candidates for applications as a biodegradable material. In this study, the ZnMg0.8Ca0.2 (wt%) alloy was prepared and treated by annealing and extrusion at various conditions. The evolution of microstructure and mechanical properties during annealing and after extrusion was performed in detail. Both annealing and extrusion caused microstructural changes influencing mechanical properties. Annealing caused a homogenization of the microstructure and transformation of metastable phases. The extrusion caused a rearrangement of the intermetallic phases, a refinement and a texturing of the zinc matrix. Those lead to a significant strengthening and to an increase in the ductility, but also to mechanical anisotropy. In this paper, the influence of the processing on the microstructure and mechanical properties is discussed in detail based on the results obtained by various methods, such as scanning and transmission electron microscopy, electron backscattered diffraction, tensile and compressive mechanical testing and nanoindentation. • Solidification mechanism of a ZnMg0.8Ca0.2 (wt%) alloy was proposed. • Formation of Zn-MgZn 2 eutectics was observed. • Influence of annealing and extrusion was studied. • Anisotropy of the extruded alloy was explained. [ABSTRACT FROM AUTHOR]

The authors cited Project No. 16-06110S in the acknowledgements of the article. Please note the correct project is Project No. 18-06110S of The Czech Science Foundation. [ABSTRACT FROM AUTHOR]

This paper is devoted to an experimental and 3D atomistic study of the influence of loading rate on fracture toughness in dilute Fe–Si alloys and in bcc iron. We analyze new and previous experimental results from fracture tests performed at room temperature on bcc iron–silicon single crystals with edge cracks (1 ¯ 10) [110] (crack plane/crack front). The specimens of single edge notch-type were loaded in tension mode I under different loading rates. The ductile–brittle behavior at the crack front was monitored online via optical microscopy together with external force and prolongation of the specimens. About 30% decrease in fracture toughness was monitored in the new experiment under the highest loading rate. The nanoscopic processes produced by the crack itself were studied at room temperature via 3D molecular dynamics (MD) simulations in bcc iron under equivalent boundary conditions as in experiments to reveal (explain) the sensitivity of the crack to loading rate. For this purpose, this MD study utilizes the self-similar character of linear fracture mechanics. The results show that the emission of blunting dislocations from the crack is the most difficult under the highest loading rate, which leads to the reduced fracture toughness of the atomistic sample. This is in a qualitative agreement with the experimental (macro) results. Moreover, MD indicates that there may be some synergetic (resonant) effect between the loading rate and thermal activation that promotes dislocation emission. [ABSTRACT FROM AUTHOR]

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

The objective of this study is to comprehensively investigate the formation mechanism of hopeite on a promising biodegradable Zn-0.8Mg-0.2Sr alloy during its self-corrosion process and its subsequent influence on the interaction of the material with cells and bacteria. Notably, the self-corrosion process of Zn-based alloys inherently generates Zn2+ ions, eliminating the necessity for additional zinc compounds in the treatment. The investigation focused on the chemical composition of the applied baths, exposure time, and temperature, in order to analyze the structure, quality, distribution, phase composition, thickness, and roughness of the resulting layers bringing range of key pros and cons for suggested materials. While the thin layers are considered more beneficial in a wide range of applications, the resulting thinnest layer was observed after exposure to the bath containing additives at 50 °C for 24 h, measuring approximately 192 ± 21 pm in thickness. In addition, the layer possessed the most homogeneous distribution under these conditions. Generally, the layers formed in the bath without additives exhibited higher thickness and rougher surfaces compared to those in the bath containing additives. Such results had a direct impact on dissolution rate, cytotoxicity, and antibacterial properties. The highest dissolution rate (40.7 mg·cm−2·day−1) indicating a limited lifetime of the layer was obtained for material processed under the following coating condition: 50 °C, 24 h, and bath without additives. The general presence of surface layers manifested in increased cell viability under direct cytotoxicity test, while smoother surface conditions also supported the antibacterial properties, both making suggested treatments as interesting variations for biodegradable zinc-based materials. [Display omitted] • Layers formed in the bath without additives exhibit higher thickness. • Layers formed in the bath without additives exhibit rougher surfaces. • The presence of fluoride anions allows the formation of MgF 2 acting as protective against dissolution. • Surface layers manifest increase cell viability under direct cytotoxicity test. • Smoother surface supports antibacterial properties. [ABSTRACT FROM AUTHOR]

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. • study of the laser shock peening (LSP) of mono- and polycrystalline copper; • residual stress caused is accumulated at the surface of the material; • dislocations are homogeneously distributed on the cross-section on the single slip plane in single crystal; • dislocations in the polycrystal are distributed heterogeneously due to different Schmid factor of individual grains. [ABSTRACT FROM AUTHOR]

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

An equiatomic CoCrFeNiMn high-entropy alloy was prepared by induction melting and a progressive combination of mechanical alloying and compaction via spark plasma sintering done at temperatures of 800 °C and 1000 °C. The chosen methods of preparation had a significant impact on the microstructure and mechanical properties of the alloy. In comparison, the as-cast alloy had a much coarser microstructure while simultaneously obtaining inferior mechanical properties compared to those of the 8-h mechanically alloyed and spark plasma sintered alloy compacted at 1000 °C, which achieved a hardness of 424 ± 7 HV, and the alloy compacted at 800 °C showed a lower but still highly comparable hardness of 352 ± 12 HV. Both alloys showed good thermal stability, as expressed by almost negligible hardness changes during 100 h of annealing at temperatures of 400 °C and 600 °C. The investigated alloys also showed their superiority during compressive stress-strain tests at ambient and elevated temperatures of 400 °C and 600 °C. At ambient temperature, the highest compressive yield strength of 1534 MPa was observed for the sample compacted at 800 °C. As the temperature of the compressive test increased, the investigated alloys reduced their compressive yield strengths. [ABSTRACT FROM AUTHOR]

• Zn-0.8Mg-0.2Sr was successfully extruded in the temperature range 150–300 °C. • Materials extruded at 150 and 200 °C dominated by fine-grained microstructure. • Elongation increased with lower extrusion temperature and higher extrusion ratio. • Various deformation mechanisms dominated under different loading. Zinc-based alloys containing elements well-tolerated by the organism (Mg, Ca, Sr) are considered as perspective biodegradable materials for an application like medical devices such as fixations of fractured bones or even stents. In the presented paper we characterize the relations between microstructure and mechanical properties of extruded Zn-0.8Mg-0.2 Sr alloy (wt%) depending on various parameters like extrusion temperature (150–300 °C) and ratio (11 or 25). Typical analysis including SEM with EBSD and mechanical tests indicate a strong dependence of obtained data on both extrusion temperature and ratio. Relatively wide range of elongation to fracture (2–22%) and anisotropy in compression yield strengths regarding loading direction (50–150 MPa) are explained by the huge effect of grain size, material texture and also the existence of dislocation substructures in materials extruded at elevated temperatures. Based on obtained results, appropriate extrusion conditions (200 °C, extrusion ratio 25) are suggested to reach the combination of superior mechanical properties 244 MPa, 324 MPa and 22% for tensile yield strength, ultimate tensile strength and elongation to fracture, respectively. [ABSTRACT FROM AUTHOR]

In this work, the formation of intermetallics in Ni–Ti system by reactive sintering at 500 and 650 °C was studied. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and the application of an experimental model consisted of nickel-plated titanium. It was found that Ti 2 Ni phase forms already at 500 °C. At 650 °C this phase undergoes a reaction with nickel to NiTi and Ni 3 Ti. The reactions were determined to be diffusion-controlled. The formation of Ni 3 Ti contributes to the porosity evolution during reactive sintering production of NiTi alloy. [ABSTRACT FROM AUTHOR]

Abstract: This work studied as-cast, T4 heat-treated and ECAPed Mg–4Zn and Mg–4Zn–0.4Ca alloys using light, scanning and transmission electron microscopy, as well as X-ray diffraction, differential scanning calorimetry and mechanical testing. The as-cast alloys consisted of α-Mg dendrites, MgZn and Ca2Mg6Zn3 phases. The T4 heat treatment led to the dissolution of the MgZn phase, but the Ca2Mg6Zn3 phase was not significantly affected by this treatment. The process of ECAP resulted in significant structural refinement, fragmentation and the precipitation of intermetallic phases. Hardness, compressive and tensile yield strengths were significantly increased by the ECAP process. Moreover, the addition of Ca had a positive effect on the mechanical properties of the magnesium alloy. The maximum ultimate tensile strength of the ECAPed Mg–4Zn–0.4Ca alloy was 250MPa. Mechanical tests at elevated temperatures and after heat treatments revealed that the ternary Mg–4Zn–0.4Ca alloy exhibited better thermal stability than the binary Mg–4Zn alloy. Differences in the mechanical behaviors of both alloys were discussed in relation to structural variations. [Copyright &y& Elsevier]

This work aims to optimize the parameters of the SHS process for the preparation of NiTi shape memory alloy to obtain a high-purity, low-porosity material. For this purpose, high heating rate (over 300 °C min−1), temperature of 1100 °C and process duration of 20 min were determined as the optimal parameters. To prevent nickel depletion of the product and to minimize the porosity, the use of coarse titanium particles (200–600 μm) with fresh surface can be recommended. SHS products were composed of NiTi with the admixture of Ti2Ni phase. The formation of this phase cannot be fully avoided in SHS preparation route. [ABSTRACT FROM AUTHOR]

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

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

In this study, we prepared a Zn-0.8Mg-0.2Sr (wt. %) alloy and processed it by ECAP. The evolution of the microstructure during the processing was observed and discussed in detail. The obtained results revealed the continuous dynamic recrystallization as the prevailing recrystallization mechanism. It affected all the aspects of the microstructure, namely the grain size, residual stresses, and dislocation arrangement. The obtained grain size was in good agreement with both empirical and theoretical relations predicting the minimal (0.4–0.6 μm) and average (2.5 μm) grain size. The compressive tests revealed the relations between alignment of the intermetallic regions, texture of the Zn matrix, and resulting mechanical performance of the material. The compressive yield strength of the material ranged from 230 to 250 MPa in the individual directions, and the tensile yield strength reached the value of approximately 200 MPa. The resulting mechanical properties were almost isotropic in the individual directions and fulfilled the basic requirements for applications in implantology, particularly, for maxillofacial, cranial or orthopaedic implants. • The average grain size of the ECAPed Zn-0.8Mg-0.2Sr alloy was 2.5 μm. • Continuous dynamic recrystallization is the prevailing recrystallization mechanism. • Intermetallic regions possess a different texture and grain size compared to the Zn matrix. • Material texture and alignment of intermetallic regions have a substantial impact on resulting mechanical properties. [ABSTRACT FROM AUTHOR]

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

An equiatomic CoCrFeNiNb alloy was prepared by conventional induction melting and by 8 h of mechanical alloying and compaction via spark plasma sintering. The alloy prepared via mechanical alloying showed a uniform ultrafine-grained microstructure composed of an FCC solid solution strengthened by HCP Laves phases. A detailed TEM inspection revealed the presence of nanocrystalline Cr 2 O 3 particles at the triple junctions of the present grains as well as stacking faults and nanotwins found exclusively in the interior of the FCC solid solution grains. The as-cast alloy had a high initial hardness of 648 ± 18 HV 30 and ultimate compressive strength of 1374 MPa. On the other hand, the mechanically alloyed alloy compacted at 1000 °C showed even higher hardness of 798 ± 9 HV 30 as well as an ultra-high strengths that reached 2412 MPa. Based on the TEM quantitative analyses considering the contributions of different structural constituents and lattice defects, the aforementioned strength value was found to be in good agreement with results from microstructure strengthening modelling, which indicated a calculated mean value of 2300 ± 300 MPa. Moreover, the mechanically alloyed alloy also showed exceptional thermal stability even after long-term annealing/testing at 600 °C because it maintained a hardness of 777 ± 5 HV 30, and strength of 2284 MPa. Image 1 • MA + SPS yield ultrafine-grained FCC + HCP (Laves) binary alloy. • The two-phases are characterized by Cr 2 O 3 at the triple grain junctions. • FCC γ-like and HCP Laves were within 200 nm. • Ultimate Compression Strength (UCS) reached 2412 MPa by compaction at 1000 °C. • TEM quantitative analysis confirmed and modelled the experimentally obtained UCS. [ABSTRACT FROM AUTHOR]