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

Zinc-based materials are intensively studied in relation to the possible application like bioabsorbable medical devices including stents or various fixation devices like screws, and plates. Zinc is favourable due to its excellent biocompatibility and rather low corrosion rate with the absence of concomitant hydrogen release making him an interesting alternative to Mg-based bioabsorbable implants. To comply with the high requirements on mechanical and degradation properties, zinc has to be appropriately alloyed and thermomechanically processed enabling significant improvement in strength and also elongation. One of the remnant shortcomings is related to the pour mechanical strength at increased temperate (even body temperature at 37 °C) and low creep resistance, both these factors are related to the low recrystallization temperature of pure zinc. In the last years, powder metallurgy techniques have been suggested to overcome the issues of low strength and poor creep behaviour, further with the tendency to support a more homogeneous corrosion process preceding the onset of localized corrosion. In this work we try to insight into the behaviour of several materials consisting of key suggested alloying elements for zinc (Mg, Ag, Sr) and processed by various techniques including conventional casting and extrusion but also powder metallurgy methods including mechanical alloying (MA) and spark plasma sintering (SPS). Our results indicated a strong positive effect of thermomechanical processing (hot extrusion) on materials microstructure with a reduced grain size of up to 2 μm and increased mechanical properties (strength, elongation). However, these results were even overcome by the application of powder metallurgy methods resulting in grain and intermetallic particle size below 1 μm and slightly improved strength over conventionally processed materials attacking 400 MPa. Furthermore, a higher tendency for uniform corrosion has been observed. In sum, powder metallurgy products are suggested as highly competitive to conventionally processed alloys. The study has been funded by the Czech Science Foundation, project 21-11439K. [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]

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

The Zn-based alloys, alloyed with the elements of the 2nd group of the periodic table, are considered as potential biodegradable materials suitable for the fabrication of small orthopaedic implants or cardiovascular stents. Unfortunately, the as-cast Zn-based alloys do not fulfil the requirements for mechanical properties for such applications. Extrusion is a thermomechanical process which is very powerful for breaking the cast microstructure and enhancing mechanical characteristics of metallic materials. In this study, we focused on the influence of extrusion parameters, such as temperature and extrusion ratio, on microstructural and mechanical characteristics of a ZnMg0.8Ca0.2 (wt.%) alloy. The extrusion led to a significant grain refinement and the formation of a crystallographic texture. Extrusion temperature played a more significant role in the mean grain size compared to the extrusion ratio (ER). At lower extrusion temperatures, the texture was less intensive and the subsequent mechanical anisotropy was weaker. Constants for the prediction of the grain size based on the Zener-Hollomon parameter were obtained. Prediction of mechanical properties using the Hall-Petch relationship appeared to be difficult because of the dependence of the texture on the extrusion temperature. Extrusion at the temperatures of 200 °C (ER = 25:1) and 150 °C (ER = 11:1) led to mechanical performance fulfilling the requirements for implantology. [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]

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]

• 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]

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]